National Academies Press: OpenBook

Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium (1958)

Chapter: Session III - Display Requirements Imposed by Visual Factors

« Previous: Session II - Methods for Controlling Ambient Illumination
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 77
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 78
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 79
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 80
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 81
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 82
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 83
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 84
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 85
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 86
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 87
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 88
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 89
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 90
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 91
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 92
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 93
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 94
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 95
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 96
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 97
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 98
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 99
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 100
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 101
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 102
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 103
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 104
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 105
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 106
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 107
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 108
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 109
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 110
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 111
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 112
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 113
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 114
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 115
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 116
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 117
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 118
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 119
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 120
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 121
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 122
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 123
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 124
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 125
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 126
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 127
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 128
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 129
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 130
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 131
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 132
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 133
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 134
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 135
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 136
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 137
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 138
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 139
Suggested Citation:"Session III - Display Requirements Imposed by Visual Factors." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 140

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

SESSION 111: DISPLAY REQUIREMENTS IMPOSED BY VISUAL FACTORS CHAIRMAN Professor Clarence H. Graham THE INTERPRETATION OF SIMULATED, ACHROMATIC, RADAR-SCOPE TARGETS Harold P. Bishop, Institute for Applied Experimental Psychology, Tufts University THE DISCRIMINATION OF SIMULATED, CHROMATIC, RADAR TARGETS Mason N. Crook, Institute for A pplied Experimental Psychology, Tufts University SOME EFFECTS OF GRID BIAS AND VIDEO INPUT LEVELS ON DETECTION WITH AN INTENSITY-MODULATED CATHODE-RAY TUBE Paul M. Hamilton, U. S. Navy Electronics Laboratory THE EFFECT OF NUMBER OF SIGNAL PUI,SES UPON SIGNAL DETECTABILITY WITH PPI SCOPES Robert L. Erdmann and Robert D. Myers, Rome Air Development Center TARGET DETECTION AS A FUNCTION OF SIGNAL-TO-NOISE RATIO, PULSE REPETITION FREQUENCY, AND SCAN RATE J. L. Piazza and I. B. Goodman, Air Arm Division, Westinghouse Electric Corporation EFFECTS OF RATE AND PROLONGED VIEWING OF RADAR SIGNAL FLICKER Anthony Debons and Charles Fried, Rome Air Development Center TARGET DETECTABILITY AS A FUNCTION OF THE AREA OF SEARCH WITH VARIOUS DEGREES OF NOISE PRESENT M. Harold Weasner, Rome Air Development Center THE PERCEPTION OF SPACE IN A THREE-DIMENSIONAL DISPLAY Walter C. Gogel, U. S. Army Medical Research Laboratory, Fort Knox 77

The Interpretation of SimulatecI, Achromatic, Raclar-Scope Targets* HAROLD P. BISHOP, Tufts University Summary-The interpretation of radar displays involves, in part, the visual separation of two adjacent targets. Two experiments were designed to measure separation thresholds as a function of target size, luminance, and amount and direction of contrast be- tween target and background, for sharply defined rectangular targets, In three other experiments, the curvature and luminance gradient of the target's edges were varied as well. Discrimination improved with luminance, contrast, and definition of target's edge. Curvature of the target's opposed edges made separation judgments unreliable. The interpretation of radar displays involves a complex of many visual functions. While discrimination of two adjacent targets is among the simpler of such functions, it is none-the-less affected by a large number of variables. Historically, work on the visual separation of two targets has been directed toward understanding the resolving mechanism of the eye. This has dictated the use of relatively simple test objects, bounded by sharp contours, usually with rectilinear and parallel edges. With this type of test object, the effects of such variables as target size, luminance, and contrast have been investigated in some detail. Radar targets not only vary in these respects, but also may have irregular outlines, contour gradients which impair the sharpness of definition, a luminance cycle related to the scanning rate, and perhaps eventually color. . ~. The purpose of this project was to investigate the discriminability of simu- iatea radar targets as affected by both classes of variables. Optical simulation of targets was employed in the interest of flexibility and precision of control. As a first step, it was considered advisable to determine separation thresholds as a function of certain classical variables. This would insure coverage of all types of variables within the same experimental context, facilitate examination of inter- actions, and perhaps help clarify the facts where the literature was in conflict. Accordingly, the first two experiments reported here were designed to obtain separation thresholds as a function of target size, luminance, and amount and direction of contrast between target and background for sharply defined, rectag- ular targets. The remaining experiments were designed to obtain comparable data on targets with edges having varying degrees of curvature and varying luminance gradients. Apparatus Basically, the apparatus is a system for the projection of two targets, one movable relative to the other, upon the back surface of a transilluminated screen, *This research was supported by the United States Air Force, under Contract OF #33(616)- 5087, monitored by the Aero Medical Laboratory, WADC. 78

with a second projector to flood the front of the screen and so provide variable contrast between background and targets. Details of the system are presented in Fig. I. In Fig. 1A, the system is shown set for the projection of dark targets. Light from the source at H illuminated the slides at S by way of the condensing lenses CL. Lateral movement of one slide was controlled from the subject's position by knob ~ via a line and pulley system to micrometer screw MS on which was mounted a calibrated dial D. Intensity of light from the target slides was controlled by filters FL and projected by the lens PL onto the back of the viewing screen VS by way of the front-surface mirrors M1 and M2. Figure 1B shows the system set for the projection of light targets. The slides at S are re- placed by a metal diaphragm with a single aperture. Light from this aperture was split by a semireflector R1. One half passed on to the viewing screen by way of the front-surface mirror M and the semireflector R2; the other half, by way of the front-surface mirror M1 and through R2. . H CL Fl Ml K ~ r k NISI | N~ n0 0 - --N ~ B Ma_-= ~ ~ Fig. 1. Apparatus: A, darl`-target protection system; B. light-target system. H. lamp housing; CL, condensing lenses; S. slides; Fl, F2, filters; PL, projection lens; Ml, M2, M3, mirrors; Rl, R2, semireflectors; MSl, MS2, micrometer screws; D, dial; VS, viewing screen; K, long; P. projector; CP, crossed Polaroids. Lateral movement of the image produced by this second beam was also con- trolled from the subject's position by way of the micrometer screw MS~' which controlled the angle of mirror M2. A calibrated dial D was mounted on this micrometer screw. Change-over from one system to another facilitated by means of a vertically sliding metal panel (not shown) on which the mirrors M1, R1 and R2 were mounted. A supplementary diffusing screen, used when targets with 79

blurred edges were desired, is not shown. This was mounted behind the viewing screen and positioned by means of third micrometer screw. Front-surface lighting was provided by the second projector P with screen illuminance controllable by means of filters F2 and the crossed Polaroids CP. Subject's head position was con- trolled by means of a chin rest and lateral guides (not shown). Procedu re In the interest of comparability with previously existing data and to expedite the testing of a large number of combinations of variables on the same individuals, a more-or-less traditional psychophysical study was indicated. Therefore, two to four subjects were used in the main experiments, and one or two in minor ex- periments. Subjects were male and female graduate students and laboratory staff between the ages of 22 and 31 with visual acuities within the range of 20/20 to 20/15. A modified method of limits was used, with the subject controlling the sepa- ration between the targets. Separation thresholds were taken as the mean of ascending and descending judgments. Such a mean is closer to the classical 50 per cent recognition threshold than judgments based on separation alone, and errors arising from sources such as anticipation, perseveration, and mechanical lag in the system would tend to cancel out. The subject was required to make two kinds of judgments: (1) starting with the targets separated, he moved them together until he could just no longer observe a separation (a "together" judgment), and (2) with the targets together, he moved them apart until he could just detect a separation (an "apart" judg ^ ~ _ ~ ^ ~ ~ ~ ~ r ~ meet). On a given trial, the subject was permitted to bracket the threshold point by moving back and forth past it but was restricted to the extent that his final adjustment had to be in the designated direction. The subjects were given un- limited time within which to make their judgments and were encouraged to make careful adjustments. In the experimental routine, subjects were dark adapted 20 min prior to commencement of an experimental period, with subsequent light adaptation to the luminance of the particular experimental conditions. Experiments 1 and 2 were concerned with the determination of separation thresholds for rectangular targets with sharp edges, ire a variety of sizes and height/width ratios and under a number of luminance and contrast conditions. . Experiment 1. In experiment 1, targets with heights of 1 1/2, and 1/8 in. and a helght/wldth ratio of A: 1 were used. Both light and dark targets were user with five contrast values varied from 0.95 to 0.10 at five luminance levels cover- ing the range from 20.5 to 0.0059 ft-l. In experiment 2 and subsequent experi- ments, a limited sampling of these luminance and contrast values was used. The values were chosen so as to effect a coverage of the range of these variables with a minimization of the total number of combinations of the experimental variables to be tested. 80

Figure ~ is a sample of the results of this experiment. Salient features of the results as a whole may be summarized as follows: ( 1 ) With decreasing luminance or contrast, thresholds rose at an accelerated rate under all cor~ditior~s of the other variables, in accordance with most data reported by previous investigators. (2) A decrease in target height tended to raise thresholds but, within the limits of the experiment, the effect was somewhat variable and generally not large. (3) With mirror exceptions, (lark-target thresholds were higher than the corre- sponding light-target thresholds. (4) Mean thresholds under favorable condi- tions were among the lowest that have been reported for minimum separation. err 4 In _ z 3 J ah 2 . 11 1 . 11 1 : 11 1 1: 1 r o ~ 8 - : ;~.~81 . i 1 1 1 LIGHT . 1 1 1 1 1/2 IN . . . . . CON TRAST .10 ~ ~ .27 o o .50 ~ ~ .66 e e - .95 0 0 ,,, 1 - _ ~ ~ 1 1 1 111 - I: .006.01 .02 .()4 .06 .1 .2 .4.6 1 2 4 6 10 20 LUMINANCE ~ FOOT- LAMBERTS Fig. 2. in terms of visual angle as a function of luminance at five contrasts for l/2-in. light targets with a height/width ratio of 2:1. Experiment 1. Separation thresholds based on "together" and "apart" scores combined, Three independent checks supported the conclusion that the dark-target thresholds were higher. A further check on the effect of background size indicated that it had no significant effect within the limits of the present experiment. Another interesting feature of these results is that, for comparable con- ditions, our thresholds drop over the region of retinal illuminance where Wil- coxi found them to rise. Hecht and Wald2 ascribed the Wilcox effect to absence of light in the surrounds, but our light-target thresholds ire this comparison were also obtained in the absence of light surrounds. Experiment 2. This was similar to experiment 1, but with the targets used having heights of 1 in. and t/8 in. and height/width ratios of 2:1, 6:~1, and 10:1. The results were generally consistent with those of experiment 1, with the further indication that a decrease in target width at a given height had relatively little effect except at low luminances arid contrasts. - ~Wilcox, W. W. The basis of the dependence of `-isual acuity on illumination. Proc. Nat. Acad. Sci., Wash., 1932, 18, 47-56. 'Hecht, S., and Wald, G. The visual acuity and intensity discrimination of Drosophila. J. Gen. Physiol., 1934, 17, 517-547. 81

Experiments 3 and 4. Thresholds were obtained using 1-, t/2-, and Run-in. targets with edges having a variety of curvatures (reciprocal of radius of curva- ture in inches). Figure 3, presenting the results obtained with the t/2-in. light target with curvatures of 0, 0.25, arid 4.0, shows a fair sample of the salient results of the experiment. Thresholds on curved edges do not fall into a systematic pattern with respect to target size, luminance, or contrast. A feature of some interest is the several negative threshold values. These, possibly, reflect both a problem of criterion of separation on the subject's part and on odd perceptual flattening of the opposed curved edges as they are brought together by the subject. Experiment 5. This was similar to experiment 1 except that the rectangular targets had blurred edges. Widths of the edge gradients, measured between the 10 and 90 per cent luminance levels, were 3.0, 4.4, and 7.1 min of visual angle. Figure 4 is a sample of the thresholds obtained under these conditions. The thresholds show the same systematic relation to the experimental variables, luminance, contrast, and target size, as noted in experiment 1. Furthermore, there was a systematic increase in magnitude with increased gradient width. 4 ,n 3 A 2 J Z 1 > o 1 I Fit- LIGHT _ C(JR\/ATlJRE _ _ CONTRoST _ .25 4.0 .9S 0-0 o--oo~ o _ _ . . ... . . ... ~)_ _~, I 1 1 1 1 1 ; L1 1 1 1111 1 ~ i, -1 .006.01 .02 04.06 .1 .2 .4 fi 1 2 4 6 10 20 L UMINANCE ~ FOOT- LAMBERTS Fig. 3. Separation thresholds based on "together" and "apart" scores combined, in terms of visual angle as a function of luminance at two contrasts for l/2-in. light targets with three edge curvatures. Experiment 4. Operational implications Salient features of the results on light targets can be summarized for in- strumental applications: Discrimination improves continuously with increasing luminance from near cone threshold to at least the region of ordinary room illumination. With rectangular targets, the higher the contrast and the sharper 82-

the edge definition the better is the discrimination, especially if the targets are small. Ever1 a small curvature of the opposed edges tends to make the separa- non judgments unreliable. In the operational situation viewing time cart be influenced by many factors, including instrumental variables such as sweep rate and rate of phosphor decay, and others, such as urgency and distracting stimuli' which are more dif- ficult to evaluate. Viewing time can be expected to influence thresholds, probably ire a more significant degree when the task is more difficult. Therefore, these data, obtained as they were with unlimited exposure time, should be regarded as limiting values in relation to operational tasks generally. 4 In 3 A 1 J > o -1 CONTRAST GRADIENT W IDTH 44' 7.1' ; _ .10 · ·.-- · ~ ~ · ~ ~.96 0 0 0--0 0 ~0 LIGHT | . . 1/2 IN . . . . . ~ I I 1 Ill I ~, , ~, ~, .006.01 .02.04.06.1 .2 .4.6 1 2 L UMINANCE - FOOT- LAMBERTS 4 6 10 20 Fig. 4. Separation thresholds based on "together" and "apart" scores combined, in terms of visual angle as a function of luminance at two contrasts for '/2-in. light targets with three edge gradients. Experiment 5. ,... _ SS __

The Discrimination of Simulatect, Chromatic, Raclar Targets. MASON N. CROOK, Tufts University. Summary Separation thresholds were measured for two sim- ulated radar targets. The targets were varied in size, curvature- of-edge, blurring-of-edge, luminance, hue, and saturation. The background was varied in luminance, hue, and saturation. Results obtained with two subjects indicate small separation thresholds under most conditions. Two blue or violet targets on a white or desaturated green background of low luminance required the greatest separation to be seen apart. Consideration of the data, in conjunction with the literature on color acuity, suggests the operation of complex interactions. This is a progress report on colored targets which were studied in a later phase of the project on which the preceding paper, concerned with achromatic targets, was based. It will minimize mental strain all around if we think of this as an exploratory study, because it was done with a large number of variables and a small number of experimental subjects in a limited time, and it raised more questions than it answered. It was terminated under pressure of other activities some time ago, but the data analysis is still going on. The general por- cedure was the same as in the achromatic phase of the program. Movable targets, controlled by the subject, were used, and "apart" and "together" judgments were called for. Apparatus An optical system was developed for completely independent control of illumination on target and background. The plan of the system is shown in Fig. 1. The subject, on the rights viewed a transilluminated viewing screen VS. An image of the targets at T was projected onto the rear of the screen by the pro- jection lens PL. In the diagram, the targets are drawn oversize; everything else is about to scale. The targets had mirror surfaces and were illuminated by light from the lamp L2. All light from L2 not reflected by the targets was absorbed by black screening. There was no glass surface in the plane of the targets, so secondary reflections were avoided. The targets were attached by transparent plastic handles to narrow rods extending from the sides of the field. Background light was supplied from the lamp L1, which uniformly illuminated an area on the screen about 5 in. in diameter except where the light was blocked by the targets. With this arrangement, the subject could view targets of any desired size or shape in a circular field, and the target and background lights did not contaminate each other. The rods supporting the targets were usually quite visible, the plastic handles faintly ~risible. The angle that the targets themselves made with the optical axis produced a slight distortion of the images and loss of focus in the outer edges, but we were concerned only with the definition of This research units supported by the United States Air Force, under Contract OF 33(616)- 3091~ I'l(~?il(~Cd by the Hero Medical Laboratory, WADC. 84

LO it, 1 ~ CLAM ; We al CL: CC \H L2 CL ~ Lb .: VS, Fig. 1. Apparatus: Ll, _ cells; F - filters; W - wedges; R - reflectors; T - targets; PL - projection lens; VS viewing scren; K - loot; S - subject; MS - micrometer screw. Target and micrometer screw oversize; other components to scale. Light dot screen indicates target-illumina tion path. ~ AS ~-1 L2 La Lb - lamps; CL - condensing lenses; CC - cooling S the juxtaposed edges, so that the qualitative imperfections of the rest of the field were not a source of disturbance. For control of hues narrow-band filters were interposed in light paths 1 and 2. The accessory paths, from lamps La and Lb, were provided with Illuminant C filters, and light from them was mixed with the monochromatic light at the semireflectors R to reduce the saturation when desired. Other components in the system were optical wedges, holders for addi- tional filters, and water cells for cooling. Filters of the Corning narrow-band-pass series used for wavelength con- trol. Luminance control was by means of photographic filters and wedges, which were slightly selective for wavelength and were, therefore, calibrated in the optical system at several points in the spectrum with a Macbeth Illuminometer. Gelatin filters were interposed on the photometer side to give an approximate wavelength match to the Corning filters on the sample side It was necessary to equate light through the several Corning filters for luminance, by flicker photometry. A sectored disc with a mirror surface was rotated in the plane of the targets and the matching field projected onto the screen being viewed from the subject's position. Triangular matches (e.g., red against white, white against blue, blue against red) showed some discrepancies, but it was possible to choose settings such that even the most deviant values were within 15 per cent of the mean for a given subject. It was necessary to change targets from time to time in the experimental routine. This sometimes resulted in slight shifts in the path of the reflected beam through the projection tense which in turn affected the luminance on the screen. For this reason, the background path was used for primary calibration, and the target path was adjusted to it by means of a homochromatic match at the begin- ning of each experimental period. 85

One target was fixed, and the other was movable by means of microme- ter screw MS' the movement being controlled by the subject through the knob K. Procedure Two experimental subjects were used. Flicker matches were made by the two separately, and luminance settings were based on matches by the subject being tested. Observation was binocular, with natural pupils, at a viewing dis- tance of 20 in. Targets were varied in size, curvature-of-edge, blurring-of-edge, luminance, hue, and saturation; background was varied in luminance, hue, and saturation. This amounted to piling several new variables on top of several variables in the achromatic phase of the program, and no attempt was made to test all com- binations. The coverage of experimental conditions was both thin and selective. For example, the higher of the two main luminances tested, 20 ft-l, was used primarily for one subject, and the lower, 0.1 ft-l for the other, with cross check- ing at selected points for the second subject at each level. Some spot testing was done, also, at 1 ft-l. The two subjects differed noticeably in their spectral sensitivity functions, but, with the procedure used, they showed a surprising degree of agreement on separation thresholds when tested under the same conditions. The primary data were obtained on targets t/8-in. high, with straight, un- blurred edges. Colors were red, green, and blue, with respective dominant wave- lengths of approximately 631, 521, and 467 ma. Three levels of saturation were used as represented by calorimetric purities of 90 to 100 per cent, 55 to 60 per cents and 0 per cent (white). Luminance contrasts were 0, 0.50, and 1.00, the target always being lighter than the ground. Secondary data were obtained on 1-in. targets, curved edges, blurred edges, and two other colors, yellow and violet. Results Results cannot be concisely summarized, either in verbal or graphic form, but a few selected curves will illustrate the general nature of the data. In Figs. 2 and 3, separation thresholds in minutes are plotted as a function of luminance as with the achromatic data in the preceding report, but, in the present instances the luminance range from 0-1 to 20 ft-1 is spread over the entire scale. Individual curves in these figures are comprised, in some cases, of data obtained from two different subjects. This method of plotting made possible the construction of more complete curves. Figure 2 shows results obtained with rectangular Run-in. targets with sharp edges. The target colors were red, green, and blue at 55 to 60 per cent purity, and the background was green throughout. The top row represents a background of 91 per cent purity' the bottom row one of 55 per cent purity. The left-hand column is for a condition of no luminance contrast, the middle column for a ~

A) 4 Lo , 3 He ~ 2 1 1 J ~ 4 > 3 2 1 O , L UM INANC E o 4~ 3t .50 x-FRED -~ GREEN °-o BLUE 9 1~% C O N T R. A S T 4 3 at. .00 . . ... .1 1. 20. 4 1 1. 20. 2- . I 1.1 20. - .t 1. 20. o ^_ L U M I N A N C E BAC K OR O U N D PUi ITY 4 o 1. 20. .1 1. 20. Fig. 2. Separation thresholds in terms of visual angle as a function of luminance, based on "together" and "apart" judgments combined, for colored targets on a green bacl~ground, at three different luminance contrasts. Upper and lower rows represent two levels of bacl~around saturation specified in calorimetric purity. Three curves in each graph represent target colors as per key, each at a purity of 55-60 per cent. Rectangular targets lapin. high with sharp edges. luminance contrast of 0.50, and the right hand column for a luminance contrast of 1.00 (dark background). The upper and lower graphs for the dark back- ground condition are duplicates. The three curves in each graph represent the target colors as indicated by the key. Perhaps the most notable feature of these data is that quite low separation thresholds were obtained under most of the experimental conditions. This appa- ratus and the apparatus described in the preceding report gave very similar, small, separation thresholds for comparable achromatic targets. One inference from the generally low thresholds is that, at these luminance levels, discrimina- tion is nearly as good on the basis of wavelength differences alone (left-hand column) as on the basis of luminance differences alone (right-hand column). ~ second feature is that a combination of the two (middle column) may in some cases be worse than either alone, as indicated especially by the point on the blue curve at 0.1 ft-1 in the lower graph. Whatever the interpretation of this particular point, we can be confident that it is no fluke. Several sets of data tend to con- firm the fact that something different was happening under these particular conditions, e.g., this is a combination on which both subjects were tested, and their two scores, plotted as the open and closed circles, almost coincide. Let us proceed to another sampling of data. Figure 3 compares different types of target edge. In this figure, we have targets of maximum saturation (in contrast to the reduced saturation of Fig. 2) viewed again against a green back- ground. The top row is 91 per cent background purity and the bottom row 55 per cent purity as before. The left-hand column is for straight, sharp edges, the middle column for curved edges, and the right-hand column for straight, blurred edges. The targets are Run-in., as before. The curved edges were semicircular, with -87-

STRAIGHT EDGES CURVED EDGES BLURRED EDGES 4 2t 01! t~ ~ .1 1. 20. By J ~ 4 . in > 3 . 2 . :'{-- ~ ~ 1 1. 20. ~1 ? 1 x ,< RED °-° BLUE 9 1 7 t 4 3 2 l BACKGROUND 4 PU l l 2 1~ l--o, 0 ~_=~ 5 5 -Jo 3 L U M I N A N C E - FT - L Fig. 3. Separation thresholds in terms of visual angle as a function of luminance, based on "together" and "apart" judgments combined, for three kinds of edge characteristics. Colored targets at maximum saturation on a green background at two saturation levels as indicated by the calorimetric purity figures in the upper and lower rows. Vertical lines through points show spread of "together" and "apart" judgments. Targets l/g-;n. high. Curved targets semicircles of l/g-in. diameter. a Run-in. diameter. The blurred edges were intended to approximate the inter- mediate gradient width of 4.4 min previously used with achromatic targets, but they were not measured and may have been somewhat wider. The vertical lines passing through the points in the graphs indicate the spread between the "to- gether" and "apart" judgments. The only target color on which comparable data were obtained under all three of these conditions was blue. In the right-hand graph, red curves are plotted, and, in the other two graphs, single red points. Note that the curves on the left show a relatively narrow spread between judgments for the two directions. This is fairly typical for straight, sharp edges, regardless of the kind of light. In the middle column, a large spread appears be- tween the "together" and "apart" values, with the latter tending to fall below zero, meaning that the targets actually overlapped when the judgment was made i this is not uncommon for curved edges under difficult conditions. On blurred edges, the most striking thing is the difference between red and blue, the latter showing not only a much higher mean threshold at the lowest luminance, but a much wider spread at both ends of the luminance scale. Discussion Let us proceed to some summary impressions. Inspection of the array of graphs for all combinations of straight, sharp-edged targets suggests that good discrimination is possible with most color combinations. The main exceptions are small, blue or violet targets on a white or desaturated green background of low luminance. Limited data for 1-in. targets were generally similar to the more extensive data for Run-in targets. Yellow targets fell into the same general pattern, 88

violet targets tended to conform to the pattern of blue targets. Such data as we have on curved edges with colored light suggest both the erratic tendencies ob- served with white light and also specific color effects. On blurred edges, the tendency to interact with wavelength is most marked for small targets and low luminances, but occurs in some degree with larger sizes and higher luminances. So far as these data have implications for operational radar, the main one would appear to be: beware of blue targets. I have referred to this discussion as "summary impressions" advisedly be- cause we are not yet sure whether we have been measuring visual functions as such, or visual functions mixed with some artifacts. An artifact is, of course, a kind of experimental weed a fact out of place. Historically, color acuity has been of interest as a means of investigating the color receptors. In that context, the question is what the retina is capable of doing, and such factors as diffraction and chromatic aberration might be though of as artifacts. In the context of our present problem, the question is what the eye as a whole is capable of doing, and the aberrations, which in all probability contribute to the character of the results on blue targets, can properly be classified as visual functions. On the other hand, if we have miscalculated with respect to the Purkinje shift and our photometric values are partly invalidated in consequence, that would be an artifact. I might say that we have not as yet found the assumption of experi- mental errors very helpful in explaining the results. One comment about the literature. In some respects the most relevant study which has come to our attention is the Eastman Kodak Company report on the influence of color contrast on visual acuity, an ND8C project which paralleled the Tiffany study. In the Eastman investigation, the test objects were Landolt Cs stamped out of Munsell papers. If I understand the Eastman results correctly, they imply a lower limit on the acuity effectiveness of color contrast alone than our data show. The comparison, of course, is somewhat indirect because of various differences in experimental conditions. Regardless of these marginal uncertain- ties, it seems safe to say that, in the field of color acuity to an even greater extent than of achromatic acuity, complex interactions are at play. Comments following Dr. Crook's Paper: Graham: The literature on color contrast is sparse, most of it having been produced in the early days of visual investigation. I should like to congratulate Dr. Crook on an experiment in a topic, color contrast, which I hope will receive in the near future a great deal more research than it has received in recent years. Knoll: I wonder if Dr. Crook would describe a little more in detail the nature of the curved targets and the reason for including them in the study. Crook: The curved targets simply consisted of two convex edges instead of two parallel edges. There might be a' question whether it makes any particular iEastman Kodak Co. Influence of color contrast on visual acuity. Report, 1944, NDRC Con- tract OEMsr-1070. -89

sense to get separation thresholds on this kind of targets. The kind of test object that have been classically used for separation thresholds are, of course, straight edges and dots. There doesn't seem to be much information on curved edges. It seemed worthwhile to include them as a kind of check, especially since the question of form is important in many of these operational situations. It was felt that it might be worth while to determine to what extent our method could be used with such targets. I think we have to conclude that the result may not be very useful. 90 .

Some Effects of Gric' Bias arc! Video Input Levels on Defection with an Intensity-Moclulatec' Cathocle-Ray Tube PAUL M. HAMILTON, U. S. Navy Electronics Laboratory Summary Measurements were made of the signaZ-to-noise ratio at threshold as a function of grid bias voltage and video input level. The experiment was designed for application of findings to a sonar display. For a given value of video input, there is an optimum value of grid bias voltage. As video noise input increases, the optimum bias decreases ~ from 38 v to 70 v in the present experiment) and becomes less critical. For the intensity-mod- ulated CRT with a P7 phosphor, the signal-to-noise ratio was consistently lower over a wide range of video inputs with a grid bias of 38 v. Results are plotted in a form useful to an engineer designing display circuits and to an operator setting grid bias and video gain. Many experiments conducted during World War II, and since, have shown that grid bias voltage is one of the most important variables affecting detection on an intensity-modulated cathode-ray-tube (CRT). Most of these experiments were concerned with the detection of target pips on noise-free scopes. In those investigations which used a noise-cluttered scope, the noise level was usually considerably below target level, and detectability was not expressed in terms of signal-to-noise ratio but merely in terms of decibels of signal attenuation from a reference voltage. In many cases, in fact, the noise level was not stated. ~. In echo-ranging sonar, the target is ordinarily detected in a background of noise and reverberation. There may be several cues for detection, none of which has been investigated adequately. Among these possible cues are difference be- tween the signal arid background returns in brightness, size, and shape. This experiment was riot designed to investigate these cues but to answer a very practical question, viz., what is the dynamic range of an inter~sity-modulated, PI CRT? Stated differently, over what range of background input levels will detection of noise- or reverberation-masked signals be optimal? Ir1 echo-ranging sonar the difference in level between the reverberation received shortly after transmission arid the reverberation or background noise at long ranges may exceed 100 db. ~ The usual method of adjusting controls on the sonar CRT display is as follows: With the video gain set at minimum, the intensity control is adjusted to give a just-visible scan line. Then, without transmitting, the video gain is increased to the point at which background noise just begins to be visible on the trace. This is probably the best technique for detecting long-range targets, which are usually marked by noise rather than reverberation. However, if the total variation of background return is near 100 db, the scope will be saturated at Poison, H. J. U. S. Navy Journal of Underwater Acoustics, 1956, 6(3), 296 (abstract). (Conficlenti<~l) . 91

short ranges and targets within this region may be missed. If a detection is made at long range, the operator adjusts the video gain and intensity controls to keep the target optimally visible while closing range. By doing this, however, he has very likely decreased video gain and intensity to the point where new targets appearing at long range will fail to reach the marking threshold of the CRT. By the use of processing techniques it is probably possible to reduce the total variation in level of the received return to values within the dynamic range of the CRT display. The primary purpose of this experiment was to find what the dynamic range of a PI CRT is. The questions we wished to answer were: What range of input levels will the CRT display adequately? Does the dynamic range of the CRT change with grid bias setting? Is there an optimum bias setting for all input levels, or does the optimum shift as background input changes? Approach We did not attempt to simulate any actual display in these tests. A high- frequency sawtooth signal was applied to the vertical deflection plates. The mixed signal and noise, consisting of a 50-msec burst of sine wave presented in a masking noise 10 kc wide at the half-power points were applied to the Z axis. A slow-speed horizontal scan provided a noise background which was relatively uniform in appearance. The edges of the trace were masked off with tape to avoid the blooming effect which occurs at high input levels and high intensity settings. The signal and noise inputs were varied with attenuators to provide a wide range of input levels. Signal levels were adequate to provide detection probabilities from O to 1.0 at any noise input. Changing the noise input level in this experiment can be considered equivalent to changing the video gain in a sonar receiver, provided signal-to-noise ratio remains constant. Grid bias settings were made with the CRT intensity control. They were measured as negative voltages between the grid and cathode of the tube with the input to the control grid (Z axis) removed. Results The detection effectiveness may be measured by the recognition differ- ential, defined as the value of signal-to-noise ratio in decibels for 50 per cent detection probability. Figure 1 shows how the recognition differential varies as a function of grid bias voltage, with input level as a parameter. The important feature of the curves is that each shows an optimum bias value. As the bias con- trol was varied at any given input level, a value was reached which gave best detection. Settings of intensity to either side of this caused detection to deteriorate. As noise input level was increased, the curves became broader and the range of bias values over which the threshold remained low was greater. In other words, with higher input levels the intensity setting was less critical. In addition, as noise input levels were increased the optimum bias values shifted to the left. This indicates that increasing input counteracts decreasing intensity, as expected. However, one interesting and unexpected feature of these results is that at the 92

highest intensity levels (in Fig. 1, 34 and 30 v), where the trace is bright even with no input, the detection performance was better in general for the higher inputs. This can be explained only on the basis of interaction between control-grid (,-axis) input and grid bias. When the Z-axis input was applied the meter used to read bias voltage deflected in the negative direction. That there was interaction is evidenced by the fact that this effect was greater for the higher intensity (more positive bias voltage) settings. Figure 2 shows how detection varied as a function of input level with grid bias voltage as the parameter. Detectability deteriorated rapidly at each end of the range input. It is apparent that the dynamic range of this particular CRT in this circuit was greatest at 38-v bias, since the recognition differential re- mained low over a wider range of inputs. This Carl be quantified in the following n S/ N AT 2 THRESHOLD IN DB -80 -70 -60 -50 -40 -30 -20 GRID BIAS VOLTAGE Fig. 1. Noise-masked thresholds as a function of grid bias voltage. v m - o - 2 ILL I O - 6 DB INPUT ~ _ 12 DS INPUT X - 18 DB INPUT O - 24 DB INPUT -42 V BIAS IS APPROX 1 1 MATE VISUAL CUTOFF 7 WITH NO Z-AXIS INPUT SAC __ . _ _ __ -10 0 -5 0 O- 34V BIAS ~ - 38 V BIAS O - 42 V B 1 AS X - 46 v Rl~ L_ _ _~_ ; . At. ~"~ 1 _ l ~ r ~ :~- 25 30 35 IN DB 5 10 15 2C MASKING NOISE INPUT LEVEL (RE 0.78V RMS) Fig. 2. Noise-masked thresholds as a function of masking-noise input level. 93-

manner: If P is the masking power' and up is signal power necessary for detec- tion' then, P + UP is the total power at detection, and the ratio (P + Pa)/P is the average signal-plus-noise/noise ratio at detection for the range of inputs 1 . 1 a:` se~ectect. For 38-v bias' this ratio is 1.4057 or 1.48 db, for input levels from 3 to 30 db (referred to 0.78 v rms). If 1.48 db, which represents the average power necessary for a just-noticeable difference on the CRT face, is divided into 27 db (the total range selected) we fired that, over this range of inputs' the observer Carl detect approximately 18.3 increments of intensity on the tube. When the same computations are made for the -34- and-42-v biases, the respective number of just-noticeable differences are 10.3 and 14.6. In terms of operator performance, then, 38-v bias gave the greatest dynamic range even though it did not provide the lowest threshold at all input levels. It should be emphasized that the particular values of bias voltage and input level in this experiment probably apply only to this particular CRT and circuit. However, the findings that bias becomes less critical and that the optimum shifts as noise input is increased should be general. The experiment confirms earlier work, which showed an optimum bias a few volts positive from the value at visual cutoff., The-42-v bias was the approximate point of visual cutoff for this CRT. It was 4 v positive from this values or at-38 v, that the tube had its greatest dynamic range. The value found for the dynamic range at the optimum bias should be general' also, in an approximate way. Figure 3 indicates that, at 38 v, the P7 CRT had a dynamic range of about 25 db. When bias is optimal and masking background uniform' the P7 tube adequately displays small changes in intensity over a range of background levels of about 25 db. Figure 3 summarizes the data from this experiment ire a way which should be valuable to the display-circuit design engineer. The curves shown are contours 25 20 NOISE 15 INPUT VOLTAGE 10 5 o X 6 D6 DIFFE EAT /~ ~` - 2 D6 ~ O O DB __ x ~ old it' ~- -70 -60 -50 -40 -30 -20 - 10 GRID BIAS VOLTAGE Fig. 3. Contours of constant recognition differential as a function of noise-input voltage and grid-bias voltage. Williams, S. D., Bartlett, N. R., and King E. Visibility on cathode-ray tube sc~eerls: screen brightness, ]. Psychol., 1948, 25, 455-466. 94

of constant recognition differential plotted against noise-input voltage on the ordinate and bias voltage on the abscissa. Combinations of bias voltage and noise input voltage can be read for a given recognition differential. These curves are also valuable to the person using this circuit as a detection display. For example, if the operator wishes to obtain an recognition differential of 6 db, his best technique is to set the bias at about 55 v and to keep his noise-input voltage between 6 and 12 v. It is evident from Fig. 3 that compression or constant-level amplification is necessary in echo-ranging sonar, where the variation of level in the return is great. The curves can be used to determine the amount of compres- sion needed to restrict the return from the ocean to values that can be adequately displayed upon a PI CRT. Comments following Mr. Hamilton's paper: R. H. Brown: I wonder if Mr. Hamilton would comment on earlier work. I believe most of the Johns Hopkins work was with a noise-free scope but there was one experiment in which they did vary the noise background. They found that the optimum bias levels remain the same regardless of the noise level, but, with increased noise, the effect of having an optimum bias was diminished. I also believe there has been some work in Canada on this problem. Hamilton: What Dr. Brown says is true. The Johns Hopkins people in some of their experiments did use a very low noise level, and they found a broadening of the curves similar to what I found, but they didn't find the shift toward the lower values of intensity. The reason for this, probably, is that their noise level was just too low. The Canadian people, also, are doing the same thing: the noise levels are very low, probably because they're working in radar and we're inter- ested in sonar. Knoll: If I recall correctly, Mr. Hamilton, you said that the scope biases and input levels were not related to luminances. Is that correct? Hamzltorz: No. They undoubtedly are, but in this experiment we were unable to make adequate luminance measurements. Knoll: This is rather unfortunate, because it would be interesting to see if your data were related, in terms of luminance and contrast, to available ex- perimental data. Since your information was obtained with a particular tube, luminance measurements for it would be very helpful information. You could simply measure the luminances on other tubes, and without having to go through the actual experimental procedure of determining thresholds, you could relate contrast information to these additional tubes. Hamilton: We were well aware of this and felt very badly that we could not make luminance measurements. However' for the dynamic situation which we had and' also because the equipment to make these measurements dynamical- ly is not available, we just weren't able to do it. We probably could have obtained relationships under static conditions between these electrical parameters and brightness on the scope. We made some attempts with what equipment we had ~5

and didn't get very reproducible results. Actually, we were interested primarily in this from an engineering standpoint. In other words, somebody came to us and asked how much compression would be needed in a particular sonar system in order to portray the sonar return adequately on a PI CRT. Graham: I should like to second the implications of this last discussion. Certain things would be a little clearer to me, for example, the relation of these findings to the data on intensity discrimination, if we did have luminance meas- urements. As you know, luminance measurements of the cathode-ray oscillo- scopes are not easy to come by, but certainly there are methods for obtaining them, and I think that if they could be expanded and more generally used' then the correlation of data on CRT viewing and such topics in the study of vision as intensity discrimination could be more readily achieved. 96

The Effect of Number of Signal Pulses Upon Signal Detectability With PP! Scopes* ROBERT L. ERDMANN and ROBERT D. MYERS, Rome Air Development Center Summary The effect of number of signal pulses upon detect- ability was studied for an AlV/FPS-3 radar indicator. By appro- priate simulating and monitoring equipment, the effect of pulse number has been examined over a wide range of indicator grid bias and noise conditions. Increasing the number of pulses in a signal reduces voltage requirements at all grid bias and noise levels. Plots for the logarithm of signal voltage against the loga- rithm of the number of signal pulses are essentially linear pro- vided grid bias is set to an optimum for prevailing noise conditions. Empirical equations for describing the data show approximately that the voltage for threshold detectability is inversely propor- t~onal to the square root of the number of pulses in the signal. Graphs of the threshold signal-to-noise ratios show reduced ratios with increased number of pulses. The complex relationship be- tween signaZ-to-noise ratio, noise levels, pulse numbers, and grid bias are discussed. This study was concerned with the effect of renumber of signal pulses upon threshold signal detection with the plan position indicator (PPI). Grid bias voltage and random noise level were selected for parameters because previous research) 2 3 has demonstrated their influence upon signal ~risibility. Grid bias voltage' controlling the screen luminance, shows an optimum range which must be empirically determined for each operating condition. As noise increases, threshold signal voltage also increases, and the influence of grid bias upon de- tectability decreases. The number of signal pulses has not specifically been the subject of previous research. However, this variable changes the brightness and size of a signal' both of which bear a positive relationship to signal detect- ability. Studies on the relation between pip size and signal detectability can be summarized briefly. Payne-Scott4 found that, with targets 2° to 12° in arc, *This report is the result of research performed by Dr. Robert D. Myers of Colgate University employed by RADC under Contract OF 30(602) 1778, end Captain Robert L. Erdmann, USAF, of RADC. The study was administered by the Intelligence Branch, Human Engineering Labora- tory, RADC, under the supervision of Dr. Philip J. Bersh, Branch Chief. The authors wish to express their appreciation to Dr. Neil R. Bartlett for suggestions concerning this research, and to Mary B. Jones and Giacomina S. Hill for their participation as subjects. Morgan, C. T. Theory and problems of radar visibility intensity-modulated scope, Naval Research Laboratory, 1952, Report 3965. Williams, S. B. Visibility on radar scopes, in Human Factors in Undersea Warfare, National Research Council, 1949, 101-130. Williams, S. B., Bartlett, N. R., and King, E. Visibility on cathode-ray tube screens: screen brightness, J. Psychol., 1948, 25, 455-466. 4Payne-Scott, R. The visibility of small echoes on radar PPI displays, Proc. Inst. Radio Eng. 1948. 36, 180-196. 97

visibility increases at the 2/3 power of target beam width. Beyond 12°, the re- lationship fails. In another size investigation, Bartlett, Williams, and Hatless studied the effect of pulse duration and arc length upon signal detection for three grid bias levels. Their results showed that, for the three biases, visibility on a decibel scale is a linear function of the logarithm of the beam width. For dim scope operation, visibility in decibels is also a linear function of the logarithm of pulse length, but this relationship changes to a curvilinear function for bright scope operation. Regrettably, these findings were for noise-free scope operation, and the effect of noise upon these relationships cannot be evaluated. During normal radar operation, some form of video noise is always present. Video noise presents false pips to the operator which must be discriminated from target pips. The frequency and voltage of noise affects the size and brightness of noise pips respectively. Low-frequency noise can produce "pips" larger than ~ A ~ ~ small target pips, and high levels of noise voltage can produce brighter ones. in addition, noise reduces signal-to-background contrast, which, in turn, reduces the luminance-difference cue available to the observer. Thus noise chances the ~ . . oetectan~ty ot all target pips, especially small ones. Small target pips ranging down to a single pulse were studied in this experiment. Method The test signals were presented on an AN/FPS-3 radar indicator using a 12DP7 cathode-ray tube. The CRT was operated with second-anode voltage at 6000 v. Other simulated electronic parameters of the CRT included a range of about 50 mix an antenna rotation rate of 10 rpm' and a pulse repetition frequency of 400 per sec. The apparatus for controlling signal presentation is shown diagramatically in Fig. 1. The first pulse generator (Pry) triggered the sweep and initiated the 5Bartlett, N. R., Williams, S. B., and lIanes, R. M. visibility on cathode-ray tube screens: the effect and size and shape of pip, I. Opt. Soc. Am., 1949, 39, 463-470. ~ (SC) I (RNG) . , , SWEEP _ AN/FPS-3 _ MONITORING . l l SCOPE 1: ( PGl2 S IGNAL _ I (db<) Fig. 1. Schematic diagram of simulation and monitoring equipment. 98

signal which vvas fed into a time delay generator (TDG). This TDG controlled signal range, which was held constant at about 21/2 in. from the scope center. Signal pulses were then fed through a signal controller (SC) which acted as a gate' controlling the time of signal presentation, number of signal pulses, and signal azimuth. These pulses from the SC were fed into another pulse generator (Phi), which controlled pulse duration and voltage. Pulses from this generator were of 1 6-v intensity and 2-,usec duration. The pulses were then fed into an attenuator, which permitted regulation of the signal voltage in 1 db steps over a 90-db range. Beyond the attenuator the signal pulses were sent directly to the grid of the CRT. Noise for this experiment was generated by a random noise generator (RNG)7 producing white noise between 30 cps and 20 kc, and fed to the grid through one of the video input amplifiers contained within the radar indicator. A calibrated oscilloscope and a root-mean-square amplimeter (RMS) were used for constant monitoring of the signal voltage' number of signal pulses, and noise voltage. Observations were carried out within a darkened booth located in a dimly lighted room. Two observers, who were practiced in CRT signal detection' were dark-adapted for 20 min prior to each test session. A metal hood shielded the scope face, and fixed the distance between the obser~rer's eyes and the scope face at 18 in. The psychophysical technique was a modified method of limits. Only ascending series were used to minimize phosphor buildup and persistence. At the start of each session the subject's visual reference intensity (VRI) was deter- mined.0 Then a predetermined grid bias voltage and noise level were simulated on the indicator. The particular grid bias values ranged from 1 to 6 above VRI in 1-v steps, and the specific noise voltages, taken as an rms measures were 0.07 (noise-free), 0.35, 0.71, 1.3, 2.2, arid 3.2 v. The experimenter alerted the subject that a test trial was starting and introduced the smallest signal. Eight values of signal size were used, represented. by signals composed of 1, 2' 3, 4, 87 12, 16, and 32 pulses. After four threshold determinations, the next larger size would be introduced and its threshold voltage determined. A threshold was ob- tained by introducing a non-visible signal and by increasing its intensity in 1-db steps on successive sweeps until its presence was reported by the observer. Since the target was introduced at different azimuths in a random fashion, the observer was required to search the scope at all times.` Four threshold determinations ';Throughout this report, grid bias is indexed with respect to VRI' which is that grid bias voltage at which the rotating sweep is just visible. This particular voltage is an estimate of "cutoff," and was stable throughout the experiment. Pilot investigations made prior to the main experiment showed that threshold voltage was essentially the sardine for searching the full scope as for searching a narrow azimuth, but that the range at which a specific signal was inserted made a systematic difference. Itched the observer was asl~^ed to disregard any signal exce,vt that appearing on the sweep line, thresholds for low brightness levels were the sardine as when he made use of both sweep and after-glow. At high- brightness levels, use of al terglow resulted in lower thresholds. For the data in this report, the observer could use both sweep and afterglow. _99_ ,-

were made on each observer at each combination of the? eight number-of-pulse values, six grid bias values, and six noise levels. Results The threshold values for each observer were quite similar; therefore' the eight threshold values (for each combination of grid bias, noise level, and num- ber of target pulses) were grouped, and the median taken as the average thres- hold.8 A small reduction in range of effect of grid bias upon signal detection occurs with small targets and low noise levels. However, in general the effects of grid bias and noise voltage are similar for all target sizes. Therefore, the largest size (32 signal pulses) was selected to depict in graphic form the effect of grid bias upon visibility, with noise as a parameter. In Fig. 2, signal voltage is represented The median was used instead of the mean because of the presence of indeterminate values, i.e., at the higher noise voltages, small signals were not visible even when presented at the maximum voltage possible with the apparatus used. ',Erdmaurl, R. L., and Gunvordahl, J. W. A comparison of two cathode-ray tubes for signal detectability as a function of random noise level RADC, 1957, TN-57-46. ~CJ/SE rev SOL rs ) 07 <r) 25 to 20 32 S/GfJA L P (JL S£S ~-Hi, l +1 + 2 + 3 + 4 + 5 ~6 GOD BIAS voL PA GE FROM V R I Fig. 2. Threshold signal voltage as a function of grid bias, with video noise voltage as the parameter. 100

on the ordinate ire decibels of attenuation from a 16-v signal. The larger is the numerical value, the less is the signal voltage requirement. Grid bias and noise level have the effect upon signal detection reported in an earlier paper.0 A change in grid bias voltage has its maximum effect upon visibility at low noise levels. A peak occurs at about +4 v from VRI. This peak represents a minimum signal requirement and, for this particular set of condi- tions, 4 v above VRI is an optimum grid bias. As noise voltage is increased, the effect of the grid bias upon signal detection progressively decreases. The addition of noise apparently shifts optimum bias slightly in the direction of VRI, but the progressive flattening of the curves makes location of the peak difficult. The curves clearly indicate that an increase in noise is accompanied by an increase in the minimum signal voltage required for detection. The change in signal voltage requirement with change in the number of signal pulses is shown for two different grid biases in Figs. 3 and 4. Signal voltage is plotted, in decibels of attenuation from 16 v, as a function of number of signal pulses' with noise as a parameter. These plots show that signal voltage decreases as the number of pulses increases. The graph also shows the typical progressive decrement in signal detectability with increasing noise level. The upper limit of signal voltage for the apparatus was 16 v, and this was not adequate to permit detection of the smaller (one- and two-pulse) signals at high noise levels. ? 25 ``, 20 an, 1 5 5 J 1 ! /V O /S E//V SOL AS . . . 0 7 XX .35 ·· . 7/ ·.& J,3 2.2 Ef-- -~ 3.2 ·~_~- · r i - . . , . 1 2 3 4 _-~ l 16 /V~MBER OF SIGNAL PAL SES 32 Fig. 3. Threshold signal voltage as a function of number of signal pulses, at various levels of video noise. Grid bias is constant at +1 volt from VRI. -101

301 ~ 20 - ~ 15 ,VO/ SE /N VOLTS (I) . 0 7 X X .~5 1 0 'I - . ~J~/--B~- 5 . ~ 1 2 3 4 _~ Gig/ D ~ / A S VOL TO SE /S ~ 4 FROM ~ ill NlJ!MB EM Of S/G~A L PUL SES Fig. 4. Threshold signal voltage as a function of number of signal pulses, at various levels of video noise. Grid bias is constant at +4 volts from VRI. _ - ~~ 32 Figure 5 shows log threshold-signal-voltage plotted as a function of log number of signal-pulses, with noise level as a parameter. Normally, the operator has control over grid bias, so that thresholds for optimum bias is a realistic index for detection capability. Accordingly, Fig. 5 was derived by using the optimum grid bias setting for each combination of noise-voltage and pulses-number. It can be seen that there is an approximate linear decrease in log threshold-signal- voltage as log number-of-pulse-returns increases. The effect of noise is to in- crease progressively the signal voltage requirement. Each curve is a least-squares fit of the data. The slopes varied slightly, but were found to approximate 0.5 for all noise levels. Thus, the equations for the data plotted in Fig. 5 have the following general form: log V K 0.510gR (1) where V represents threshold signal voltage' R. number of pulse returns, and K, an empirical constant whose value is determined by such variables as pulse repetition frequency antenna rotation rate' anode voltage' tube type' and noise level. -102

t/O/SE /~/ SOL 1.251 1 ,00 0.75 _J 0 5 ~ O . 2 5 0.00' id_ at' - ~\ \ ~ = O7 . . - 35 J . 3 = 2 - 3.2 -~.~1 ~- 0.00 0.25 0 50 0 .75 1 .00 LoG fIJUMBE~ OF 5~ L PAL S£S Fig. 5. Log threshold-signal-voltage as a function of log number-of-signal-pulses for an optimum grid bias setting. Video noise voltage is the parameter. 1 25 1 50 is Although this constant is an empirical one, noise level was a variable in this experiment, and a rough idea of its contribution to the constant may be derived by plotting log threshold-signal-voltage as a function of noise voltage, with number of pulses as a parameter. This type of plot is shown in Fig. 6. Figure 6 was derived from Fig. 5. While the data actually show a sigmoid trend, straight lines fitted by the least-squares method provide a reasonably good approximation. Thus, the relationship between threshold signal voltage and rms noise voltage may be considered to be roughly semilogarithmic in character for the range of noise values investigated in the present experiment. The curve of one pulse represents the ordinate intercept (K) values for Fig. 5. Using the least-squares linear solution for this set of values, a general equation for the data of Fig. 5 was derived: log V 0.7 + 0.3N 0.5 log R (2) where V represents signal voltage, N stands for noise voltage, and R is the num- ber of signal pulses. 103-

P/JLSE fJ(JMBEf?S O / .__ _ ~ ~ 2,0- ' ewe .~. ~ /6 1.5 1.0 O. 5 O .0 32 it_ ~ - , 3;,. ~ a. ~ - lo, - - _ -~ - .69e 1 _ 4 . 16 0.0 0.5 /.0 /.5 2,0 2.5 3.0 3.5 //O/SE VOLTAGE (EM S J Fig. 6. Log threshold-signal-voltage plotted against noise voltage, with number of signal pulses as the parameter. An attempt was matte to lit tubs equation to all the data of Fig.5. The re- sulting straight lines were found to fit three sets of points quite well. For the other three sets' the lines were systematically above the datum points, partly due to rounding approximations in the general equation. It should be noted that a shift of 0.1 log unit or less on the ordinate would provide a good fit for these data as well. Signal-to-noise ratio values are considered to be more meaningful for engi- neering purposes than absolute signal voltage measures. Accordingly the data of Fig. 5 are plotted in Fig. 7 as threshold signal-to-noise ratio in db as a function of log number-of-signal-pulses. Each curve reflects the linear nature of the data in Fig. 5. Signal-to-noise- ratio is seen to be an inverse function of both number-of-pulses and noise voltage. Other experimenters using a more extended range of noise voltage, have found that signal-to-noise ratio passes through a minimum when plotted as a function of noise. This is suggested in the present experiment by the overlap of the curves for the two highest noise levels. In fact' for 8 or 12 pulses, signal-to-noise ratio seems to have already passed through a minimum at about 2.2v. It is also probable ~ · ~ ~ · · ~ .` ~ ~ 1 · 1 that, If determination of threshold signal voltage could have been obtained for one and two signal pulses at the two highest noise levels (2.2 and 3.2 v) ~ the resulting 10Corso, J. F., Crocetti, C. P., and Page, D. E. Human engineering evaluation of Rome Air Development Center experimental operation room, RADC, 1952, TR-52-27. Confidential. 104

~ c ~200 ~ , /5 1 /0 - ~ 5 n 'an 'I `_ ' ~ ~` i\"'' ~`'§~\` i"~'\35 at\. `: ~ 7/ /.3 \ 2.2 '. 3.2 050 /,00 LOG /~/UMBER OF S/GNA L PAL SES A/0/5£ VOLFaGE \ l 2.00 Fig. 7. Signal-to-noise ratio in decibels shown as a function of number of signal pulses for an optimum grid bias, with video noise voltage as the parameter. overall function would have been curved rather than linear. This notion is sup- ported by the data of Lawson and Uhlenbeck~i in dealing with the influence of beaten angle upon signal detection. Small beam angles (which correspond to small target pips) result in the target's requiring more than the expected power to be seen. The mean slope of the best-fit lines presented in Fig. 7 corresponds closely to the slope of-0.5 reported by them for the linear portion of their signal- to-noise ratio vs. beam-angle data. Discussion The complex interrelations among the variables which influence the physical characteristics of the stimulus, the related changes these stimulus characteristics produce in visual functions, and the changes in the operator's task with variations in the physical stimulus all require careful analysis if signal Risibility is to be predicted from knowledge of electronic variables. When the pip on a PPI presentation is increased in size by increasing the number of signal pulses' the effect is somewhat analogous to holding all other electronic variables constant while increasing beam width. Other methods of changing size have a different effect upon signal presentation. For example, if the number of signal pulses is held constant and size is increased by increasing Bylaws n, J. L., and Uhlenbeck, G. E. Threshold Signals. McGraw-Hill, 1950. ~105

antenna rotation rate, there is ~ related reduction in the brightness of both signal and background. If size is held constant and the number of pulses increased, either by decreasing antenna rotation rate or by increasing pulse repetition frequency there is a related increase in the brightness of both background and signal. Thus, holding pulse repetition frequency and antenna rotation rate con- stant, as in this experiments maintains a constant background brightness, and the main effect of increasing the number of signal pulses is to enlarge the pip area. These two effects upon the physical stimuli (changing background luminance and changing area) have well-known corresponding effects upon the visual functions of the eye.)' Important here is the fact that increasing either area or luminance reduces the contrast ratio required for brightness discrimination. Contrast and area relationships are not the only stimulus cues involved in signal detection. The edges of the pip have a gradient contour; small pips take less time to appear than large pips; and pips are present longer for bright scope operation than for dim scope operation. This greater duration of a pip gives the observer time to rescan or refixate on the pip area. Thus, added time increases the probability of signal detection. The addition of noise further complicates the analysis in at least two ways: it increases the scope brightness' and the addition of noise pips distracts the ob- server and interferes with the detection of signal pips. When noise pips are added to the screen, the operator begins to utilize shape cues in addition to lumi- nance differences in making the required distinction between noise and signal pips. As noise voltage is increased, the signal-to-background contrast ratio is re- duced, and the noise pips cover a range of luminance both brighter and dimmer than target pips. Thus, as the brightness cue becomes less important, the shape cue becomes more important. Changes in pip area change the shape cue. Possibly, in this study, the failure to discriminate small pips from noise pips under high noise levels is due to reduced shape cues. In view of these complex relations, it is surprising to find that the relation- ship between log threshold-signal-voltage and log number-of-signal-pulses can be adequately described by a linear equation. The form of equation 1 is such as to suggest that retinal integration accounts for much of the relationship. Equation 1 states that threshold signal voltage is inversely proportional to the square root of the number of signal pulses. If signal voltage is assumed to represent lumi- nance, and if number of signal pulses is assumed to represent area, then equa- tion 1 is the same as Piper's Law for area-intensity threshold relations in the human eye. Although there are important differences between the type of data described by Piper's Law and the data of this experiment' i.e.' differences in conditions of observation' retinal location and range of retinal image sizes, the similarity can- not be ignored. In spite of the complex effects of electronic variables this simi- larity suggests that the relationship between signal voltage and number of pulses can be adequately explained in terms of retinal integration. Wood worth, R., and Schlosberg7 H. Experimental Psychology. Holt, 1C)54, 93. 106-

Comments following the paper by Erdmann and Myers: Graham: In generals what is the time interval between successive pulses? Erdmann: We used an antenna rotation rate of 10 rpm and a pulse repetion rate of 400 pulses per see; thus 1/400 see between individual pulses. We intro- duced t'ne signal on each successive sweep until it was detected by the observer, but it appeared in a different place on the scope with each sweep. Essentially, there was considerable time between signals. Azimuth presentation was random in nature. We limited our sessions to 1 hr to prevent any fatigue from occurring throughout the experiment. I would like to comment on a point made during the discussion of the pre- vious paper, to the effect that we need luminance measurements from a cathode- ray tube to go from our visual data to data on cathode-ray tubes. This very im- portant measurement is extremely difficult to obtain. Even after you have it, it doesn't do the engineer too much good to be given data in vision terms. To design his radar set, he needs to know the translation from your vision char- acteristics to his electronic variables. The shape of the pip is related to second anode voltage which also controls the spread effect; there are so many variables involved that he really needs data taken with cathode-ray tubes themselves. Graham: I wonder if I may ask another question. You made the state- ment that' because we have a logarithmic relation between two of the variables investigated' the "comparability" between this rule and Piper's law should not be overlooked? - 7 Erdmann: I just added that as an interesting afterthought, since num- ber of pulses actually determined the area of the signal and signal voltage con- trolled brightness. Piper's law should probably not be used to explain the data of this experiment. Crost: In relation to both of the two previous papers' there is a great deal of data on cathode-ray tubes which may be of help; I'm sure that they haven't really been overlooked' but maybe they just haven't been known. In general' the current in the beam of a cathode-ray tube corresponds to some form of cubic equation with respect to drive voltage above the cut-off voltage of that tube. Because of the cubic relation, for a signal-to-noise ratio greater than unity, it's advantageous to operate with a higher background, because the signals' being above the noise, give a greater light output on the screen with relation to the background, but still he sees the pips at a considerably higher brightness level since the brightness on the CRT corresponds almost linearly to the current in the beam. Also, with the PI screens, the question of the time-spacing between hits is of great importance because of the buildup characteristics of the screen and the time of delay between pulses The faster the pulses appear on the screen for a given number of hits, the better is detectability' because each time the beam current hits the screen, there is an added increment of brightness. Consequently, this enhances visibility. 107

I don't know the exact relationship between brightness at the screen and the visibility function of detectability. This is something that people who actually work in psychological vision would have to determine. But I do know that from the engineering point-of-view it is advantageous, when you have greater-than- unity signal-to-noise ratio, to use a higher brightness level and also to increase the speed of the repetition of the hits. Below the noise level, there's a different situation because both voltages are operating in the same region. The main dis- criminatory function below the noise level is the shape of the pip, since the noise is random and the pip should have some degree of correlation. 108

Target Detection as a Function of Signal-to-Noise Ratio Pulse Repetition Frequency, arc! Scan Rate J. L. PIAZZa and 1. B. GOODMAN, Westinghouse Electric Corporation Summary-The sir~gle-look probability of detection is a function of prf, scan rate, and S/N. Increasing prf from 800 to 1000 pulses per sec offers little prospect of increase in probability of detection. There is an almost linear decrease of probability of detection as scan rate increases. S/N acts in a linear fashion and produces the largest effect of any of the parameters of the experiment. It appears, also, that scan rate and prf act independently in affect- ing the detectability of a target. This paper deals with the first in a series of experiments on the detection problems of airborne radar systems. The experiment was performed to show the effect of scan rate" pulse repetition frequency, and signal-to-noise ratio on the single-look probability of detection of a target. The equipment simulated a radar with a Palmer-type scan and "B"-type presentation of the target information. Method of approach The indicator employed a cathode-ray tube with a P7 phosphor. The B-scan simulator supplied the indicator with the azimuth and range sweeps and the video information consisting of both target signal and noise. The simulator was devised in such a manner that scan rate, pulse repetition frequency (prf) and signal-to-noise (S/N) could be quickly changed. The indicator consisted of a K1381 P7 CRT and its high voltage supply. The indicator was mounted on a stand with the CRT centered on a 3.5 in. square opening in the face plate of the stand. The face plate was 2 ft square and was painted a flat grey. The indicator face was inclined, away from the observer, at an angle of 30° from the vertical and was located approximately 28 in. from the observer. A 3x3-in. matrix was placed directly onto the CRT face for use in identifying target locations. The B-scan simulator (Fig. 1) produced four azimuth sweeps and then blanked the indicator 8 see; this constituted a single trial. After the 8-see quies- cent time, a second trial was begun. The target was produced only on the third azimuth sweep. Two azimuth sweeps, containing only noise, preceded the ap- pearance of the target, and one followed the target's appearance. The simulator produced the target in any one of nine positions on the indicator face. Scan rate, pulse repetition frequency, and signal-to-noise ratio were variables. A system of switches and relays allowed the rapid changing of the nine positions, as well as three values for each of the other parameters. A timer controlled off-time of the B-scan by disabling the azimuth sweep generator, as shown in Fig 1. The azimuth sweep generator produced the signal for azimuth motion of the B-scan at the rate of 50, 100, and 120 degrees per sec. This signal was fed into the amplifier which supplied azimuth deflection signals 109

to the horizontal deflection plates of the indicator. Dither signal was fed in' along with the azimuth deflection signals, to produce the proper B-scan. The dither signal was a 50-c sine wave whose peak-to-peak voltage was of such amplitude as to move the range sweep horizontally over an interval of two degrees on the indicator face. The output of the azimuth sweep generator was also fed to both the scan selector and azimuth position selector. The scan selector was a count- ing device, which gated the mixer to produce the target on the proper scan, while the azimuth selector gated the mixer to produce the target at the proper azimuth position. Output of the prf generator was fed to the mixer, pedestal generator, and range-sweep generator. The prf generator could be switched to 500, 800, or 1000 pulses per sec. The pulses to the mixer were allowed to pass through on coincidence of the scan and azimuth position gates. The azimuth position gate was so produced that the target could be located at any of three azimuth locations. The width of the azimuth-position selector gate determined the number of pulses. :3 I .vr ~ ~ Lo I L; ~ ~ _ ME ~ 1~L:~I ~r ~ . ~ AZ. POS. | r~HER I 1 1 ~-'~ PULSE PER TARGET PRF SCAN RATE 500 800 1000 50 28 43 54 100 1 2 2 1 27 120 1 0 1 7 25 Fig. 1. B-Sweep simulator block diagram. SYSTEM VALUES SCAN RATE 50,100, 120 DEG/SEC DITHER 50 CPS PRF 500, 800, 1000 PPS ANT BEAM WIDTH 2.9 DEG OFFSET ANGLE 1.0 DEG LOBING FREQUENCY 50 CPS I NDICATOR USABLE AREA 3.5X3.5 INCHES AZ WIDTH 120 DEG CRT SPOT SIZE 1.0 MM RANGE SWEEP 300,u SEC PULSE WIDTH i.2 USES S/N +6,+2,-2 DB IF BAND WIDTH 1.1 MCS VIDEO BAND WIDTH I MCS A study was made of the formation of a target on a B-scan to determine the number of equal-amplitude pulses required to produce a simulated targets The system to be simulated was chosen to have an antenna half-power beam- width of 2.9°, an offset angle of 1° and a robing frequency of 50 c. The indicator of the system had a useful face of 3.5x3.5 in., the width of which was chosen to correspond to 120°. The spot size of the indicator was ~ mm in diameter. The distribution of the target returns on the Indicator ot the system was determined for the various prfs and scan rates used. The target return distribution was used to determine the build-up, or integration' of the returns on the indicator. Compu- tations were made to determine the number of equal-amplitude pulses which, distributed in the same manner' would very closely duplicate the integrated target return. The results of this study were used to determine the number of ~Piazza, J. L., and Volertas, V. F. Westinghouse Electric Corporation, Air Arm Division, Systems Analysis Section Technical Menzo. In preparation. 110

pulses to produce a target in the simulation. Figure 1 gives the number of pulses for each combination of scan rate and prf. The pedestal generator also was fed a signal from the prf generator to pro- duce an unblanking pulse, which allowed the video to be displayed over a range sweep only. The range-sweep generator received its signal from the pry generator and produced a sweep of linear rise of 300 ,usec duration. This signal was fed to the vertical deflection amplifier and thence to the vertical deflection plates of the CRT. The range sweep, thus, began at the bottom of the usable area of the CRT and rose linearly, the full 3.5 in. to the top of the display area, in 300 ,usec. The mixer output (a pulse train which occurrect on the proper scan and at the proper azimuth position) was fed into the range position generator, which produced delayed 1.2 ,usec pulses and modulated them at I-F frequency. The amount of delay, with respect to the start of the range sweep, determined the target's vertical position and could be rapidly changed to produce a target at any one of three vertical vertical positions. The pulse train was then fed into the I-F mixer. The I-F mixer also received the output of the noise generator, which was set up so that three different noise levels could be selected with signal-to-noise ratios of +6, +2, and-2 db. The noise and signal (pulse train) were mixed and sent to the I-F pre- and post-amplifiers, which had a bandwidth of 1.1 me. The video output was fed into the video amplifiers, which had a bandwidth of 1 me, and was combined with the pedestal and fed into the CRT. There were 243 trials, nine for each combination of the different values of the experimental variables. Since three values were used for each variable, there were 27 different combinations. Each combination appeared once in each of the nine different positions on the indicator. These positions were denoted by the 3-by-3-in. matrix scribed on the face of the CRT, each position being located in a different cell of the matrix. Each cell of the matrix was identified by a letter and a number. The letters A, B. and C were used to represent the columns of the matrix (from left to right) while the numbers 1, 2, and 3 were used to signify the rows (from top to bottom). Four males having normal 20/20 vision volunteered to act as observers. None had had any experience as radar operators. The four observers were tested once a day for three days. Each day, they were shown targets generated under every combination of the experimental values and appearing in every position. Targets were presented in a random order with the restriction that every possible condition be used once during a session. A condition was specified as one combination of the experimental variables and one location on the CRT. A trial lasted a duration equivalent to four sweeps of the B-sweep and each trial was separated by an interval of 8 sec. One target was shown on each trial. Only one observer was tested at a time. He responded by calling out the letter and number that identified the cell in which he saw a target. If he did not see the target, he made no response. The experi- menter recorded the results. At the beginning of the first session, each observer was instructed in the task from a prepared sheet. He was not told when 111-

a target would appear, nor was he told how many targts would appear. The method of designating a target's position was explained and he was asked to respond when a target was seen. No control was exercised over the ambient illumination. During the ex- periment, each observer wore a headset into which audio noise was introduced. This was done to mask any outside sounds that could distract him from his task. Results The measure of performance was the number of correct identifications of target position. Each correct identification was given a score of one. Each time a target was identified incorrectly, or not detected, a score of zero was given. Since for every combination of experimental parameters the target appeared once in every position, a score ranging from O to 9 was possible for each com- bination. This score was divided by nine to yield the single-look probability of detection in the graphical treatment of the results. A five-way analysis of variance was performed with the number of correct identifications of target position as the dependent variable and with signal-to- noise ratio, pulse repetition frequency, antenna scan rate, observers, and replica- tions as the main sources of variance. The results of this analysis showed that all main effects are statistically significant at the 0.001 level and that all first-order interactions with signal-to-noise ratio are significant at the same level. A plot of single-look probability of detection (,PD`) VS. pry for various S/Ns is shown in Fig. 2. The mean PD for the various prfs is shown as a broken-line curve. At higher S/N (+6 db) changing prf has very little effect, over the region covered while at lower S/N (+2 db) the effect of prf is more pronounced. In any case, it appears that increasing prf above 800 pulses per second will yield 10- ~I =- 080 c~ ,, 060- o J ~ 040- o cat by o J 020- J CO of 0.00 S/N , 1 1 500 800 1 coo PRF Fig. 2. Single-look probability of detection vs. pulse repetition frequency. 112-

little return. The curve for 2 db S/N is well below a PD of 0.1 over its full extent. The effect of scan rate is shown graphically in Fig. 3. The mean PD for the various scan rates is shown as a broken line. It appears that PD exhibits an almost linear decrease with increase in scan rate. There seems to be no flattening of the curves in the region of interest. The lower scan rates are most desirable since any increase in scan rate results in lowering the single-look probability of detection. ~ .o o 0.80 C~ LL LL ° 060- CO o 0.40- tar: by to o J 1 020- At In o too - _ _ _ _ _ , SIN _ -2 SCAN RATE 100 Fig. 3. S;ngl~loolc probability of detection vs. scan rate IS/N parameter). t20 A plot of probability of detection vs. scan rate with pry as a parameter is shown in Fig. 4. The mean probability of detection for the various scan rates is ~ .o c] o.eo - z O ~ 0.60 L'J to J 0.4 o- - ~S to G y 0.20 to no 1 J Z 0.00- ~0 PRF 10 00 so SCAN RATE Fig. 4. Single-look probability of detection vs. scan rate (prf parameter). 113 1 20

shown as the broken-line curve. These curves exhibit a linear decrease in PD with increase in scan rate. They also show the saturating effect of prf. The change in PD of the two curves for pry of 800 and 1000 pulses per sec are almost identi- cal. There would be small gain in P., for further increase of prf. The effect of S/N on the probability of detection is shown in Fig. 5; the curve is very nearly linear. From the curve it can be seen that, for a Pn of 0.5, a mean S/N of +3 db is required for the various prfs and scan rates. The effect of S/N on PD is quite large-S/N exhibited the largest effect in the experiment. It is of interest to study the effects of hits per scan experimentally since this variable has been considered the sensitive parameter in performing analytical studies on the problems of radar detection. Hits per scan are a function of scan' rate and pry, and there should be a significant interaction between scan rate and prf. In our results, there was no significant interaction between these var- iables. A plot of Pn vs. hits per scan is shown in Fig. 6. Smooth curves were drawn between the points of equal prf. It does not seem that one smooth curve could be drawn between all of the points. The curve for a prf of 500 approaches an asymptote, but the curves for prfs of 800 and 1000 continue to increase as the number of hits per scan is increased. With the same data, the points of equal scan rate were connected, as shown in Fig. 7. The curves approach an asymptote. The curves for higher scan rates? 100 and 120 degrees per see, seem to saturate at a level of PD below that of the lower scan rate of 50 degrees per sec. to o.e . c, ~0 6- He o - C~ ~ 04 o tD 02 o o o 2 SIGNAL-TO-NOISE RATIO (db) Fig. 5. Probability of detection vs. S/N. 4 J/ 1 . 1 / 6 From inspection of Fig. 6 and Fig. 7, it would seem that hits per scan Is not a sufficient criterion for prediction of performance, but may suffice as a first order approximation. The value of PD is not completely dependent on the num- ber of hits per scan. Scan rate and prf each independently act in their own way to influence the ability to detect a target. 114

1.0 0.8 - z o '_ 0.6 Lo O 0.4 J or m O 0.2 PRF =800 PPS -- P R F = 1OOO PPS PRF =500PPS t ~ 25 30 35 40 . 1 1 1 1 o L 5 10 15 20 Hl TS PER SCAN Fig. 6. Probability of detection vs. hits per scan {prf parameter). 10- 1 0.8 ~ 0.6 o - Led ~ 04- o 3 0.2 cr m o CL t 2100°/ SEC et,' ~ 50°/ SEC .-~ w = 1 20°/SEC 0 ~ ~ 5 1 0 ~ 5 20 25 HIT S PER SCAN . 0 35 40 Fig. 7. Probability of detection vs. hits per scan (scan rate parameter). 115

Comments following the paper by Piazza and Goodman: Graham: Thank you, Mr. Piazza. I should like to ask a question concerning the rate of the pulse repetition. As I remember, you were dealing with pulse repetition rates of many hundreds per see, so this is an entirely different order of magnitude from the pulse repetition rate discussed by Captain Erdmann. Is that correct, Captain Erdmann? Erdmann: No. I used a pulse repetition rate of 400 per sec. Graham: The problem I'm interested in, of course, is the way in which pulse rates summate within the limits of a critical duration according, presum- ably, to the Bunsen-Roscoe Law. This problem finally merges with the general problem of flicker and is, from a theoretical point-of-view, clearly related to the kinds of things that have been discussed this morning. 116

Effects of Rate arc' Prolongec' Viewing of Raclar Signal Flicker* ANTHONY DEBONS and CHARLES FRIED, Rome Air Development Center Summary Some radar scopes present lights which flicker at varying rates. Personnel contemplating the use of these scopes suggested the possibility that the viewing of flickering lights over a prolonged period of time might cause deleterious effects on the scope observer. Lights flickering at the rate of 4, 8, or 12 c were presented on a simulated radar scope for periods up to 2 hr to de- termine whether or not prolonged viewing did affect observer performance. Nine observers were asked to report continuously the number of non-flickering lights (1 to 4) presented on a simu- lated 19-in. radar scope when these were randomly interspersed among a large number of flickering lights. The experimenter in- troduced changes in the number of non-flickering lights in a pre- programmed, but random, fashion at intervals varying randomly from 6 to 60 sec. Each of the subjects was tested for periods of 30, 60, and 120 min on one of the flicker-rate conditions. Three addi- tional subjects were tested under similar conditions, but with the non-flickering lights presented in the absence of the flickering lights. Three of the nine subjects were also tested on all four con- ditions of flicker rate for a 30-min period. The observers in every case were asked to respond as quickly and accurately as possible to changes in the number of non-flickering lights. The data of the experiment revealed that the lower is the flicker rate of the field lights, the shorter is the time required to respond correctly to changes in the number of non-fZickering lights on the scope. With high rates, both latency and variability in performance in- creased. All the subjects were able to complete 2 hr of testing without any subjective effects, nor were there any systematic changes in latency during the course of a session. , The present problem arose ire connection with the proposed integration of the Army Missile Master System with jointly used air defense radars. The in- tegration would result in presentation to the operators of target information on the scope in the form of flickering lights. A number of reports, both formal and informal, have suggested that exposure to flickering lights over extended periods of time may produce deleterious effects on observer performance., The ex- periment described in this report was designed to investigate the influence of prolonged viewing of the flickering lights on response latency and to determine any subjective effects. *The authors wish to thank Dr. Ned R. Bartlett for his considerable help in this experiment and Dr. Philip J. Bersh for editing the paper. Hewlett, G. Flicker sickness. Archives of Ophthalmology, 1953, 50, 685-687. Walter, V., and Walter, G. W. The Central Effects of Rhythmic Sensory Stimulation. Electroencephalog. & Clinical Neurophysiol. 1949, 1, 57-86. -117

Method and procedure A 19-in. circular display simulating the actual radar scope of the missile master system was used. The display consisted of 12 miniature neon lamps with total illuminance of approximately 1 ft-c, which provided flicker at 47 8, or 12 c, depending on the condition programmed by the experimenter. One to four non-flickering lights were also presented to permit the measurement of response latency as a function of prolonged viewing of the flickering lights. Both the number and position of these non-flickering lights were controlled by the experi- menter from an adjoining room and were varied by him in a preprogrammed, but random, fashion. Changes in the number of non-flickering lights were pro- grammed to occur at intervals varying at random from 6 to 60 see throughout a session. The test room was dark, and the display was illuminated only by a wide-band blue light of approximately 1 ft-c illuminance. A control panel of four buttons was positioned directly in front of the dis- play to enable the subject to report any changes in the number of non-flickering lights appearing among the flickering lights. Recording was accomplished by means of two electronic timers. One of these, which ran continuously from the start of a session, recorded elapsed time for the session. The second clock was also activated at the start of each session. Whenever the experimenter introduced a change in the number of non-flickering lights, this response clock was stopped. As soon as a subject pressed the correct response button, the clock was again activated. An incorrect response by the subject had no effect upon the response timer. Thus, the total time required by the subject to respond correctly to changes in the number of non-flickering lights could be obtained by subtracting the response clock reading from that of the first timer. Readings were taken by the experimenter every 5 min and provided a basis for measuring the cumulative latency of correct responses by successive 5-min intervals throughout a session. Twelve adult male subjects possessing normal vision according to clinical standards were used in the experiment. The subjects were randomly divided into four equal groups. Each of three groups was tested at one of the flicker rates fin., 4, 8, or 12 c) for the twelve background lights; the fourth group, serving as a control, was required to respond to changes in the number of non-flickering lights in the absence of the flickering lights. All subjects were given three test sessions, lasting 30, 60, and 120 min. respectively. In a follow-up session, three of the subjects previously used were tested on all four conditions for 30 min. The subjects were seated in front of the display at normal radar viewing distance and were required to fool; at the display continuously. They were in- structed to depress the button on the panel appropriate to the number of non- flickering lights appearing on the display. At the termination of each session, the subject was taken out of the test booth for a 10-min rest period, after which he was tested again for another 10 min. During the rest period each subject was asked how long he could continue on this task and whether he had any difficulty paying attention to the onset of the lights. - 118

All conditions (both flicker and session duration) for the main and follovv- up experiments were counter-balanced. Results There were no subjective reports of discomfort or annoyance resulting from the flicker at the end of 30-, 60-' and 120-min periods. F'rom the standpoint of subjective comfort, there appears to be no reason to be concerned about using tags of low luminance that flicker. The cumulative latency was calculated for correct responses to changes in the number of non-flickering lights made by each subject during an entire session. These cumulative latencies were expressed as percentages of the session length. The median latency in sec for each of the four groups during the 30-' 60-, and 120- min sessions are plotted for 15-min intervals in Figs. 1, 2, and 3, respectively. Each point was obtained by determining the cumulative latency of correct re- sponses made by each subject during a specified 15-min interval and by com- puting a median for the three subjects in each flicker rate group. An c:, z ~ 4 I1J In z Lo 3 z . o In `~ 2 _ z Or In 1 .- .12 c :\\ ·4 C N8 C ~·0 1 C O O 15 30 TIME OF WATCH IN MINUTES Fig. 1. Effect of varying flicker rate on response time for 30-min session. 119

5 v) 7 0 4 LL] in I3J ~ 3 - LU in as o in in: lo o Although the data for individual subjects from which these plots were de- rived show considerable variability in latency during a session, the cumulative latency for the last 5 min of a session remained essentially the same for each subject as during the initial 5 min. When subjects were given a 10-min rest after the 120-min session and then tested again' the rest period did not change the final level of performance. It will be noted from Figs. 1' 2, and 3 that the functions for the various flicker rates tend to be displaced systematically on the ordinate, with the higher rates apparently increasing the latency of correct responses. In order to verify this phenomenon, three subjects were tested for 30 min on each of the three flicker-rate conditions, as well as on the control condition. Data from this addi . Mona experiment are contained in Fig. 4. Figure 4 presents the median response latency in seconds for three sub- jects as accumulated over each 5-min interval of the 30-min session. It will be seen from Fig. 4 that the time to respond to changes in the number of non-flick- ing lights increases correspondingly as flicker rate of the background lights is A \12 C :,'8 C ~4 C ·0 C I ~ 0 15 30 4 5 60 TIME OF WATCH IN MINUTES Fig. 2. Effect of varying flicker rate on response time for 60-m~n session. 120 c' cat I1J in Lit in z 0 in c,

increased. As might be expected, the subjects responded most quickly to the onset of the non-flickering lights when these tags were presented in the absence of any flickering lights. . ~_ o) 4 he o CD As - 3 LLI U. He 2 2 UO A / n I I , , , I \_~ ~ARC - _ . ~4 C 1_ _ 1 105 120 0 15 30 45 10 75 90 TIME Of WATCH N MINUTES Fig. 3. Effect of varying flicker rate on response time for 1 20-min session. 5 4 - ~ 2 In - - _ 12 C i ~ 8 C e4 C ~0 C 30 10 20 TIME Of WaTCH IN MINUTES Fig. 4. Effects on median response time for three subjects exposed to each flicker condition. -121

Discussion The main objective of the present experiment was to determine the effects of viewing flickering lights otter an extended period of time. No reports of dis- comfort occurred even after two hours of viewing. These results do not agree with earlier findings, '' that extended viewing of flickering light by both clinical and normal subjects resulted in such effects as nausea7 headache, fatigue, etc. The differences in experimental conditions and the difference in results ob- tained7 however, suggest that factors such as the dimensions of light sources, the number of sources, and the level and spectral composition of the illumination may be critical in determining the effects of prolonged exposure to flickering light. The present study was initiated to check the possibility that some of tlie existing Air Force radar soonest which possess the flicl~erin~ characteristics ~~ ~~~~~~ ~~~r-~7 ------ i- - ~ closely simulated in the current experiment, might induce subjective etlects detrimental to the operation of an element critical to an air defense system. Due to the differences in approach, test conditions used7 and methodology, the find- ings of Ulett1 and Walters are not directly applicable, either to this experiment or to the operational situation in question. In relating the data to applied problems, it might be asked how the latencies obtained from the experiment compare with the irreducible time lag to be ex- pected by virtue of limitations in the capacity of the human to respond to visual stimuli. Lemmon studied the reaction of subjects to lights contained on two frames presented adjacent to one other. ~ The subjects were asked to discriminate the number of lights appearing on the two frames. He obtained an average re- action time of approximately 0.6 see for responding to 1 to 4 lights. If this average reaction time is applied directly to the current data7 it becomes evident that the correction is far from enough to account for the total lag in responding to changes in the number of non-flickering lights. Apparently the task of this experiment involved added factors of search and decision making. The measure used to determine any behavioral change was time to respond correctly to a change in the number of r~on-flickering lights when these were pre- sented among continuously flickering lights. It was found that latency did not show any increase after two hours of viewing. However7 a finding of particular interest is the difference in performance obtained as a function of the flicker rate of the field lights. The smallest latency was obtained for non-flickering lights presented alone. When these non-flickering lights were presented among flick- ering lights7 an increase in flicker rate increased the variability and latency of responses to the non-flickering lights. These findings are consistent with the hypothesis that what may be involved is a discrimination task varying in diffi- culty. Conceptually, the lowest flicker rate represents the case of least difficulty inasmuch as the differences between the non-flickering and flickering lights are large. As the flicker rate is increased7 the differences between the non-flickering and flickering lights are diminished, with the consequence that the discrimination task increases in difficulty. In other words7 the higher the flicker rate, the more :iWoodworth, R. S. Experimental Psychology, Molt, 1938, p. 335. -122-

nearly does a flickering light approach a steady light in appearance. These find- ings on flicker rate can be translated into operational meaningfulness by relating the data to equipment which requires minimum latency in responding correctly to a varying number of lights, only some of which may flicker. It would seem that care must be taken to differentiate clearly the lights to which responses must be made from those which must be viewed continuously by the observer. Comments following the paper by Debons and Fried: Graham: Colonel Debons, I wonder if you would tell me again the con- ditions of the subject in this situation and what he was doing. Debons: The experiment consisted essentially of looking continuously at a 19-in. display simulating the radars used in the Army missile master system. There were four steady lights presented against a background of twelve flicker- ing lights. Periodically, the experimenter changed randomly the location and number of the steady lights. The subject responded to the changes in the number of steady lights by pressing the appropriate button in the control panel located directly in front of the display. Wiseman: This is reminiscent of our studier on flickering light in which we had all sorts of reports of people having deleterious effects-for want of a better word from the flicker. When we go to the laboratory, we get people who say: "I think if this goes on I will become sick, I think I will become dizzy." But we were never, in the laboratory, able actually to make anyone pass out or get sick enough to vomit. As a result of your experiment with twelve people, you say you notice no effects. Can you convince the people who actually performed the experiment in the first place that they did not get sick? Or do you have any explanation as to why people originally got sick and your people didn't? Debons: Correspondence received at RADC has not related the background behind the finding of nausea. We tried to get the facts but to the best of our knowledge these were not available. The conclusion as to the nausea effects remained speculative. We felt, therefore, that we should explore the conclusion in a general way to see what shows up. There was some evidence in the literature in terms of the Walter and Walter experiment and the Utlett experiment that would seem to indicate that looking at a flickering light causes nausea. After testing approximately 300 normal and 600 clinical subjects, Walter et al came out with evidence that exposure to a large flickering light causes nausea in both groups, the extent of the effect being a function of the clinical status of the sub ~7 sect. Walter talks about using a 82,000-ft-c source thrown directly at the eye of the individual for about half an hour. The subjects showed symptoms of nausea. This problem has been of interest to me for some time. While I was a WADC, I exposed four subjects to a display simulating a radar scope for five hours con tinuously. During this time, the subjects were asked to identify letter forms on the display in terms of azimuth and range. The display face changed in brightness like the phosphor decay function of the usual radar scope. There were no nausea effects, no sickness. I don't believe we are in a position to be too convincing to -123

anyone at this stage of the game' however. There is so much controversial evi- dence in the literature, and the stimulus parameters from one experiment are not exactly replicated in another. Needless to say, what is needed is a rigorous and systematic study of the whole problem. Graham: Colonel Debons makes it seem almost certain to me that you wouldn't get nausea looking at cathode-ray tubes. On the other hand, although I'm certainly no expert in this field and may simply be impressed by old wives' tales, is it not a fact that motion sickness does occur? Can it not be induced by providing moving detail in the environment of a subject? It seems to me that you might have obtained nausea if you had used very large targets and very large figures rotating, at an appropriate rate. Do you think this is possible? this area. Debons: Yes sir, the stimulus parameters seem to be very important in Graham: What you're interested in is finding out whether or not CRT viewing will lead to nausea. Is that it? Or are you interested in the general problem of motion sickness? Debons: The problem of flickering signals pertains to a number of radar systems. We will never solve the problem of flicker and nausea if we design our experiments based upon our experience with radar scopes alone. The general problem of the effects of visual flicker is of more general interest, I believe. Last winter' I visited the Army center having the radar scopes in question to see whether the display in the experiment approximated the operational scopes. The experiment duplicated exactly the size of scope and flicker rate. The lights on our display were closer to the orange end of the spectrum, while the scope display appeared to offer signals closer to the blue end. Our lights were slightly larger than the radar signals. As far as our response measure is concerned, our arrangement does repre- sent a departure from the operational situation. I might add, however, that our response measure was simply a fabrication to elicit the alleged nausea effects. Initially, we were not interested in performance decrement for its own sake just whether or not the individuals became sick by virtue of looking at the scope. 124

Target Delectability as a Function of the Area of Search with Various Degrees of Noise Present M. HAROLD WEASNER, Rome Air Development Center Summary Twenty subjects were tested to determine the effects of varying restricted search area upon target detectability in the presence of noise. The six restricted areas ranged from 0.1875 to 6.0 in. Four noise levelss light, medium, heavy, and no noise, were utilized. The noise, targets, and rings were projected by means of 35-mm slides. Time and accuracy of detection were the response measures. An analysis of the data revealed that ( 1 ) any area restriction results in the improvement of detectability as compared to performance in the non-restricted area situation, and (2) target detectability improves as the area of seach is delimited to circles with diameters of 1.5 in. or less. Noise on a radar scope generally increases time, and reduces accuracy, of detection and tracking of signals. The noise level may be such that the observer will never detect the signal or, if he does detect it, will lose it in the background noise. Grease-pencil marks have long been used as aids for keeping detected targets under surveillance. These are used primarily to remind the operator where the target was last seen. With just a few targets, the scope becomes very cluttered with grease-pencil tracks and notations. An aid to be considered-is an electronically generated ring around a target. The initial size of this ring can be adjusted for the target's speed and can increase ire diameter with each sweep at a rate governed by the target speed. The present study was designed to investigate the effects of restricting search area on target detection in the presence of noise. Specifically, the hypoth- esis this experiment investigated is how time and probability of detection of signals are functions of search area. Review of the experimental literature reveals few studies relating to target detection. However' Williams et all reported that detectability decreases as a function of increased scope size. Another of their findings was that detectability is inversely related to search area when the ratio of pip size to scope size remains constant. A study by Buckley, Hanes, and Deese' revealed that detection thres- holds are lower for a 3.5-in. PPI than for a 7-in. PPI. In general, the limited data reported in the literature impose the need for further research on the relation- ship among the critical variables which influence target detectability. 1 Apparatus and procedure The noise, targets, and rings were sketched on paper, photographed, and made into 35-mm slides. Figure 1 shows a sketch of the experimental setup. Williams, S. B., Wolin, B. R.7 Bare7 J. K.7 Wagman7 W. and Hageman7 K. Operator efficiency as a function of scope size. Rome Air Development Center, 1954, Technical Report 55-18. ~Buckley, B. B.7 Hanes7 R. M. and Deese, J. E. Search area and target detectability on a PPI cathode ray tube. Wright Air Development Center, 1953, Technical Report 52 303. -125-

Two 35-mm projectors were used, each with a NTariac to control lamp voltage. The subjects viewed the flashed opal screen from approximately 18 in. One pro- jector presented the noise slides, and the other one projected the slides wit-in target and ring. Accessory equipment permitted the experimenter to determine reaction time to approximately 0.01 sect and further' to record whether the sub , ject reported a target. Reaction time, or latency, in this experiment was defined as the time between onset of the stimulus and the subject's response. Twenty subjects received ten pretested familiarization trials and 120 test trials. Thirty trials for each of four stimulus conditions were presented to the subjects in a randomized order. ~ O B oE3 A - POWER SUPPLY B-VARIACS C-CLOCK D-CONTROL SWITCHES E- NOISE PROJECTOR F-SIGNAL PROJECTOR - EXPERIMENTER H- OPAL FLASHED SCREEN 1- SUBJECT Fig. . . Diagramatic representation of apparatus. The conditions were as follows: (1) ring and target; (2) ring and no tar- get; (3) target and no ring; and (4) no target and no ring. The subjects did not receive any knowledge of results during the test trials. Five slides of each of six ring sizes constituted the 30 slides for the ring and target condition. The inside diameter of the rings subtended visual angles of 0.6°, 1.2°, 2.4°, 4.8°, 9.5°, and 19.0°. The total viewing area subtended a visual angle of 36.8°. The center of the ring was located 3 ill. from the center of the a · ~ · · _ l A TO ~ Q~0 00~0 21 ~° ~ Ot the renter of the area. circular viewing area at ]~-7 1~-~ ~ ~ O1~ ~ Ally AL Alp ~ Hi The targets were located within the ring two-thirds of the distance out from the center at 0°, 90°, 180°, 270°, and sometimes in the center of the ring. The targets were always oriented perpendicular to a radius of the viewing circle. All targets were 0.03 in. wide and 0.125 in. long (visual angle of 0.4°~. 126

During the 120 trials, there were four noise conditions (one of which was presented along with each slide). The noise slide was changed after every five trials; it was on continuously during the five trials. The four noise levels were: O (no noise at all), 1 (light noise), 3 (medium), and 5 (heavy) . Four groups of five subjects each viewed the 120 test slides each croup with a different noise slide sequence. Results and discussion l _7 ~=_---r The results, in terms of group averages, are plotted in Fig. 2. The results show that, when a target is present, rings with diameters as great as 1.5 in. improve detection, regardless of noise condition. The functions for the largest search areas show a decrease in detection for all noise conditions. The no-noise condition resulted in 100 per cent accuracy. As the amount of noise increases the probability of detection decreases. With no ring in the 12-in diameter area, the percentages of correctly identified targets are 80, 65, and 39 for light, medium, and heavy noise, respectively. too 90 _ 7n . _ 60 o 40 _ 30 __ 20 1 _ 10 _ TARGET PRESENT NO NOISE ~ \ Gino`\. " \ "` W\ "` an\ .~% - \ ,/' NOISE CONDITION NONE -- LIG HT ~ - MEDIUM onto HEAVY ~ LIGHT / NOISE / / / in I' \2 " %% ,,\ MEDIUM NOI SE $. H EAVY NOIS E 3/16 3/8 3/4 1 1/2 3 6 CIRCLE DIAMETER IN INCHES (EQUAL LOG AREA INTERVALS Fig. 2. Per cent correct responses with target present, as a function of circle size. These findings clearly indicate that, although noise decreases target de- tectability, this effect is reduced by restricting search area. Within the limits of this experiment. target detectability imnrn~res corre.snondin~l~r n.s the search - ~ ; ~ ~ ~ --or- --r---~---~-a area is reduced. Figure 3 shows the results for all noise and circle-size conditions when no target was present. The percentage of correct responses ranged from 88 to 127-

10O7 indicating that the subjects were not guessing and that they generally did not report targets when there were none present. TARGET NOT PRESENT 100 90 80 70 60 A: A: 50 40 30 20 10 ~, NOISE CONDITION NON E -- Ll GHT ~ MEDIUM onto HEAVY ) 1 1 1 - ~X ~-X~, ~__=- = ~ _ _ 3J16 3/8 3^ 1 1/2 3 6 12 CIRCLE DIAMETER IN INCHES (EQUAL LOG AREA INTERVALS ) Fig. 3. Percent correct responses with ~arg.et absent, as a function of circle size. Figure 4 shows that, when a target is present, the median latency of the correct responses falls between 0.6 and 2.0 sec. The total viewing area yielded more rapid detection than the two largest restricted areas. It must be remembered that subjects aetectecl fewer targets when viewing the entire display. Did the presence of the ring in the two largest restricted areas encourage the subjects to assume that a target was present and thereby, increase their search time? It would be of value to investigate restricted areas ranging between the 12-in. display and the largest restricted area in this experiment. Figure 5 shows the median latency for correct responses when no target is present. The data indicate that a latency for no-noise condition lies between 0.75 and 1.0 see, regardless of area. Latency for the other noise concretions ~n · 1 . ~ creases with area size. The latencies for the total viewing area for the light, medium, and heavy noise conditions are 5.6, 6.2, and 6.3 see, respectively. In general, the results indicate that within the limits of this experiment, any restriction of the search area is an improvement over utilizing a non-restrict- ed area, and that target detection is best for search diameters of 1.5 in. or less. These results show that placing a ring around a target improves the detection of targets in the presence of noise. However, prior to making a firm recommenda lion for inclusion of this electronic arcs, it Is necessary to investigate these variables with dynamic CRT displays. In addition, other variables, such as noise config- urations, multiple targets, moving targets, reinforcement, target size, and the presentation time, should be investigated. 128-

2.0~ 1.9~ 1.8 1.7 en z1~6 ° 1.5 In Z I.4 z 1.3 ~ 1.2 - Z 1.1 1.0 a .7 _ TARGET PRESENT- CORRECT RESPONSES NOISE CONDITION NONE LIGHT ~ - MEDIUM onto HEAVY J ,~ .... , ,... ,^ . . i<\ ,' ~ ,, , - H EAVY \'` NOISE \: MEDIUM \ NOISE Ll GHT NOISE .6 _ O _ 3/16 3/8 3/4 1~/2 3 6 12 CIRCLE DIAMETER IN INCHES (EQUAL LOG AREA INTERVALS ) Fig. 4. Median latency {seconds) of correct responses with target present, as a function of circle size. TARGET NOT PRESENT- CORRECT RESPONSES 7.0~ 6.5 6.0 ~ 5.5 _ - ~n 5.0 _ o <A 4.5 _ on z 4.0 _ - 3.5 ~ 3.0 z 2.5 ~ ~0 - 15 1.0 .5 o NOISE CONDITION NONE -- LIGHT ~ - MEDIUM 0~0 HEAVY 1/: / i' -~ m'~ t~ S----C--r-----~ I 1 1 1 1 1 ~6 3/8 3/4 1~2 3 6 12 CIRCLE DIAMETER IN INCHES (EQUAL LOG AREA INTERVALS) HEAVY NOIS E MEDIUM ,,' iNO ISE i' · LIGHT ~NOISE / at,' /," /..' ~ NO NOISE Fig. 5. Median latency {seconds} of correct responses with target absent, as a function of circle size. 129

Comments following Weasner's paper: Graham: Thank you, Mr. Weasner, for a very interesting and very clear result. I know that a number of people here are interested in the general problem of detection and search. Anonymous: During a study performed at Ohio State University several years ago, when the number of presentations per min were increased, the sub- ject seemed to develop a greater drive and incentive to look harder for his targets and thus performed considerably better. Weasner: As I mentioned, we thought about limiting the stimulus time but in this initial investigation, we wanted to see how long people would take if they were not pressed. Of course, we realize that if you would compress the time in which subjects have to respond, they would probably increase accuracy and cut down on their detection times as contrasted with the free situation. - 130

The Perception of Space in a Three-Dimensional Display WALTER C. GOGEL, U. S. Army Meclical Research Laboratory Summary-Perceptions ire three-dimensional space are examined with particular reference to the perceptions of frontal size, depth between objects, arid three-dimensional shape. Major attention is paid to the relations between the visual and physical world. After derivation of equations for the perceived depth between objects, predictions are made. Similarly, there is a detailed mathematical analysis of the perception of three-dimensional shape. It is reasonable to expect that the use of the depth dimension ir1 addition to the two frontal dimensions will result in an increase in the efficiency with which a display can convey certain kinds of information. For example, the suggestion has been considered that the depth dimension be introduced in the radar scope by using a stereoscopic presentation.~-4 This paper will discuss some of the scaling problems involved in different types of judgments in a three-dimensional display, where the perceived depth component is produced by stereoscopic cues. Perceptions in three-dimensional space v Several types of perceptual judgemeIlts which might be required can be considered with the aid of Fig. 1. Here the eyes of the observer are represented at the left' with A indicating the interpupillary distance. A frontal extent (S) and depth extent (X) are presented at distances De and Do from the observer. In the upper part of Fig. 1' the two frontal widths Se and Sg are shown as having angular frontal sizes be arid be while in the lower part of Fig. 1, the two depth intervals Xef and X 7h are shown as producing the binocular disparities orb- OLf and OLn OCh. Table l gives a notation relating extents in visual space to ~ . . . . . ~ . . . . ~ ~ 1 1 . 1 _ _ _ 1_ ~ _ _ ~ corresponding extents in physical space. This notation will be used througnout this paper. It is assumed that within the intervals Xef and X'h of Fig. 1 only the binocular disparity cue is present to produce the perceived extents t(°`e rife), and (~7 ah) Table 1. A notation for Perceived and Physical Space and the Correspondence between Them. Perceived Ee ED (lye off), (log ah), Physical angular the 8g (lye off) (Cry ah) Physical linear se Sg Fief XDh iBaker, A. and Grether, W. F. Visual presentation of information. Wright Air Development Center, 1954, Technical Report 54-160. 2Fitts, P. M. Engineering psychology and equipment design. In Handbook of Experimental Psychology, Wiley, 1951, 1287-1340. 3Coher~, J. Binocular disparity as a coding dimension for pictorial instrument and radar dis plays. Wright Air Development Center, 1955, Technical Report 55-393. 4Gebhard, J. W. Visual Display of Complex Information. In Human Factors in Undersea Warfare, National Research Council, 1949, 39-66. - 131

A - - 1~ Sg e ~Xef 9 ~Xgh it' f ~e: / thy ~ Fig. 1. Schematic diagram for considering several types of judgments in a three- dimensional stereoscopic display. A. Perceptions of frontal size Perceptions of frontal size might involve judgments of the perceived sizes Ee and E7 of Sc end S7. Or, perhaps more Ire quently, the perceptual ratio Ee/Eg would be involved. Often, in frontal size ex- periments, Se is adjusted until EC Eg. If the resulting value of Se is such that Se So, this is termed perfect frontal size constancy. If, however, the resulting value of Se is such that (e §L,, this is termed zero frontal size constancy. Over frontal size constancy would be the case in which Ee < Ed when Se SD. B. Perceptions of the depth between objects Perceptions of the depth between objects would involve the perceived sizes (are Offs' and (cY7-Ah)' or more frequently their perceived ratio. A common type of problem would be to determine, given a particular value of Xef, the size of Xgh required in order for (ore atf), to equal (a(9 °th)~- A special case of this type of judgment would be the perception of the midpoint of a depth interval. C. Perceptions of three-dimensional shape It will be seen in Fig. 1 that the frontal size Se' together with the depth interval Xef, defines an object having a frontal and a depth component and thus a particular three-dimensional shape. The perceived shape of this (the nearer) object is designated (ore cYf)~/Ee and the perceived shape of the more distant object is designated (ag ah)'/Eg. A particular problem would involves for example, predicting the physical extents required in order for (cYe CYf)~iEe to be equal to (fig a},/Eg. -132

Relations between the visual and physical world A. Perceptions of frontal size-[frontal size judgments have been investi- gated under conditions in which binocular factors apparently played a critical role. The results indicate that under these conditions considerable frontal con- stancy and sometimes over frontal constancy was present throughout an ap- preciable portion of the visual field.~~7 B. Perception of the depth between objects 1. Equations for perceived depth The experimental investigation of the relation between perceived and physical space when using binocular disparity cues has produced evidence for a simple relation between these two dimen- sions.~-~i This relation given in the notation of Fig. 1 and Table 1 is that: (I cte al )) (I (he ~ af) He Abe (1) Equation 1 states that the ratio of the perceived depth to the perceived frontal extent is proportional to the ratio of the binocular disparity to the angular size of the frontal extent. The constant of proportionality is 1/C where C is assumed to be an individual constant. The left side of equation 1 represents a perceived three-dimensional shape. A perceived depth extent can be defined by rearranging equation 1 as follows: (ache-CXf) `,e ~ ~ C f) (2~) The term Ee/6'e in equation 2 is the perceived size per unit of angular frontal size at the distance De and is therefore (within limits) independent of the size Se used in its determination. In general, the perceived frontal size per unit of angular frontal size at any distance Dv is EV/§V. There are reasons for considering that the right side of equation 2 should be written in differential form. If this is done with do substituted for ore ctf' equation 2 becomes: e e idol' 1 r E1; do (3) ((he turf) C J (v r r Chalmers, E. L. Monocular and binocular cues in the perception of size and distance. Amer. J. Psychol., 1952,65,415 423. ~Hermans, T. G. The relationship J. Exp. PsychoZ., 1954,48,204-208. 7Holway, A. H. and Boring, E. G. Determinants of apparent visual size with distance variant. Amer. J. Psychol., 1941,54,21-37. Morel, W. C. Perceived frontal size as a determiner of perceived stereoscopic depth. U. S. Army Medical Research Laboratory, 1957, Report 296. 9Gogel, W. C. An observer constant in the perception of stereoscopic depth. U. S. Army Med- ical Research Laboratory, 1957, Report 316. ~°Gogel, W. C. The perception of shape from binocular disparity cues. U. S. Army Medical Research Laboratory, 1958, Report 331. Vogel, W. C. Apparent depth duplication with binocular disparity cues. U. S. Army Med- icaZ Research Laboratory, (in press). of convergence and elevation changes to judgments of size. 133

It is necessary only to specify Ev/~, as a function of ax to find a useable ex- pression for (ae-aft. For this purpose, consider the following relation: E7, _ {Dcit' Ee \, Do ) Where Ee is the perceived size of a frontal extent S at De and Ev is the perceived size of the same frontal extent at Dv. When n-0, from equation 4, Ev Ee Equation 5 states that when n 0, the perceived size of S is always the same independent of its distance from the observer. This is the case of perfect frontal size constancy mentioned above. When n 1, equation 4 becomes: (4) E7, De E,: Dv (6) Equation 6 states that when n = 1, the perceived size of the constant physical size S varies inversely with distance, i.e., directly with jV7 the angular retinal size of S. This is the case of zero frontal constancy noted above. When n 1, equation 4 becomes: E7, D7, Ee De Equation 7 states that a constant size S of frontal extent increases linearly in its apparent size with an increase in distance. This is a particular case of over frontal size constancy. Therefore, n is a measure of the amount of frontal size constancy in a situation. For simplicity, it will be assumed that, for a particular set of conditions, n remains constant throughout the portion of the visual field being considered. The perceived size Ee of S at distance De can be written as follows: Ee-Kne S and, En' the perceived size of S at Do, can be expressed as: Ey _ Kn9 S or, in general, EV the perceived size of S at Dv is: Ev Knv S (7) (8) (10) Equation 10 states that the perceived size of S at a particular distance can be expressed as the physical size (S) multiplied by a constant (K), where K' as indicated by the subscripts n and v, may vary as a function of the distance Dv and the amount of frontal constancy n. It is easily demonstrated by combining equations 4, 8, and 9 that: Kne Den Kng Den Two additional relations are helpful. These are: A cat in radians D 134 (11) (12)

and, S id in radians D where A is the interpupillary distance of the observer. Combining equations 3, 4' 8, 12, and 13 gives: e e (eve Hi)' red CAD ~-J~v7l-ly ~(14) ( 13) t ~ From equation 14, specific equations are derived readily for any value of n. Also, by means of equations 12 and 13, the resulting equations can be expressed either in angular or linear terms. For the present purposes only certain of these derived equations will be considered. 2. Predictions from equations for perceived depth Referring to Fig. 1, the problem is to determine the size of X97t which will be perceptually equal to (or in the more general case be some perceived multiple of) the perceived size of Xef. Consider the case in which Xef and Xgh are perceived as equal. Equa- tion 14 specifies the perceived size of Xe:, i.e.7 (are Orf)~. The perceived size of Xgh' i.e., (~9 Ah)', iS similarly written. ~ Knq Don ( ~ ) and if h (~e °`f)~- (~D °eh)~, then 9 ~ Jan n- 1 do (15) e ~ Knot Do 5~ c~vn-l d<x _ Kilo Dot J~aVn-1 do (16) r h From equation 11, equation 16 becomes: e g at (Yvn - 1 dCY 5~ <lVn - 1 do ( 1 7 ) t h When n 1 (over frontal constancy)7 equation 17, after integrating, applying equation 12, and simplifying, becomes: Fief Xgh (18) Similarly, when n O (perfect frontal constancy), equation 17 becomes: xef De - X 7h DD tar, when 7z +1 (zero frontal constancy), equation 17 becomes: Xef D 2 Xgh D9~ -135 (19) (20)

It seems, therefore, that the amount of physical depth required to reproduce the same apparent depth interval using binocular disparity cues is the same at all distances when n -1, increases directly with distance when n 0, and increases approximately as the square of the distance when n 1. From the frontal size constancy studies noted previously, it appears that not all of these different amounts of frontal constancy are equally likely to occur. However, ob- servers will differ in the amount of frontal constancy they evidence in a ar- ticular binocular situation and the above equations indicate the direction of the consequences of these differences. 3. Perception of a midpoint Suppose that a depth interval Xe~ is presented and the observer is asked to adjust an object f to the apparent mid- point of this interval. In this case, (cue orf), _ (af ag)' It is readily demon- strated in a manner similar to that used in deriving equations 18, 19, and 20 that, when n 1, and, when n-O. or, when n +1, Do-De Df 2 Df :/ De TV D 2 De D' f De + Do (21 ) (22) (23) Thus we find that, depending upon the amount of frontal constancy present, the perceived midpoint can be at the arithmetic mean, at the geometric mean, or at some more incorrect position. C. Perception of three-dimensional shape 1. Equations for perceived shape The equation for the perception of the shape of a three-dimensional object, or a comparison between the perceived shape of several of these objects, is derived readily from equation 14. For this purpose, let the perceived shape be called m such that me ~ ore-O`f :) From equations 8, 14, and 24, Den c me = S. CAT-1 J an do (24) (25) Equation 25 not only defines the perceived shape me but it is also useful in de- termining C. For example' if me 1, i.e., the frontal and depth extents are per- ceived as being equal, then, c S An-1 136 (26) ,.

From equation 25, and when m_ 1~ m - Den ~ or n Se CA- \ n ,' C _ De ~ `~ n ale ~ S. An-1 ~nJ (27) (28) As before, specific equations for m and C for particular values of n are readily derived from equations 25 through 28. 2. Predictions from equations for perceived shape-From equations 12 and 27: me e r_ r_ _~1 CSe l n \Den Die)] (29) Consider the case in which a physically constant size of frontal extent S is located at two distances De and D`, from the observer. At distance De a depth interval Xef is adjusted to appear me times as large as Ee' the perceived size of S at De. A1SO7 at Dg a depth interval X9h is adjusted to appear m`; times as large as E7, the perceived size of S at Dg. Suppose that the value of m in the two cases is identical, i.e., me-me. What will be the physical shapes required to produce these two perceptually equal shapes? This question can be answered from equa- tion 29 when C has been experimentally determined previously by using equation 28. How will the physical depth components of the perceptually equal shapes vary as a function of frontal size constancy? This question can also be answered by considering equation 29. Since the ms in the two cases are identical, Den A ~ 1 ~ NIL ~ ill Don A ~ 1 ~ ~ ~ )1 (302) CS ~ n ~ Den Din JO C S ~ n ~Dgn Dhn/] which, when simplified, gives: or. De D9 Df Dh (31 ) Xef De ( 32) X9h Dg Since the term n does not appear in equations 31 and 32, this means that these relations are not changed by the amount of frontal size constancy present. From equation 32, the change in the depth X required to maintain a constant perceived shape of a three-dimensional object of constant frontal size S increases linearly with distance, independent of the amount of frontal constancy present. But, from equation 29, the amount of binocular disparity or linear depth required to produce a particular value of m for a particular value of S is not independent of n. Also, if a constant value of ~ is used instead of a constant value of S. the change in X as a function of D required in order to keep m constant is not independent of n. -137 r

Equation 32 as derived from equation 30 applies only when S is the same value at all distances. Conclusions ~. . It is obvious from the previous discussion that the amount of frontal con- stancy present is considered to be important in determining the perception of cteptn resulting from a binocular disparity. The role of the observer constant C was less discussed. It will be seen that C is important in the determination of a perceived shape and a perceived depth extent (equations 25 and 14~. There is considerable evidence that observers often show large reliable differences in the perception of a three-dimensional shape. This is attributed largely to differences in individual values of C.9-~t It is clear, therefore, that if we are to understand the judgments which an observer will make in a three-dimensional binocular display, we must know something about his values of n and C. This does not mean that both n and C are important or are equally important in all types of stereoscopic spatial judgments. As discussed previously' C was not considered to be significant in the perceived ratio of two depth intervals or the perceived ratio of two shapes. In the latter perceived ratio, a circumstance was considered in which the value of n was also not significant. The previous equations specify some factors which should be measured if perceived events are to be predicted. In addition, these equations specify the particular judgments in which these factors are important. This type of information is of value if it is desired, for example, to produce perceptually equal intervals in the stereoscopic display' or more generally, to predict what the observer will see. All this assumes, of course, that the only cue to the perceived distance be- tween the pair of objects is the binocular disparity cue from these objects. When the binocular disparity cues between one of the pairs of objects and additional objects is considered, or when other cue systems are introduced to influence the perception of the depth interval, the situation may become more comple.~° Cer- tainly, additional experimental data are needed, not only to test further the va- lidity of the point of view presented in the above equations, but to extend our information concerning the psychophysical scaling of three-dimensional space to increasingly complex situations. Comments following Dr. Gogel's paper: Graham: Thank you' Dr. Gogel' for this valuable and interesting discussion. In my opinion, this is a very impressive presentation. Dr. Gogel starts with the fundamental concept that the important thing in depth perception is retinal disparity and then, in a systematic, clear-cut way' carries the development to other areas of the psychology of depth, i.e., depth constancy' shape discrimina- tion' and other topics. The consideration of the latter topics was one of the claims to value and importance of Luneburg's account; but I do think that Gogel's account, if it is validated in an appropriate way, will take into consideration more psychological effects than does the Luneburg account at present. - 138

This account, I think, will have-again I say if it is validated a good influence on the psychology of depth perception. It is sometimes said that if you are paying most of your atteention to retinal disparity, geometrical optics, and topics of that sort, you are not really a psychologist; you are something else. A real psychologist (it is implied) deals only with the phenomena of space, and of course mathematics is of extremely secondary interest in this connection. This attitude has led in the past to what I call a schizophrenic cleavage in the study of depth. If you are a psychologist, you study the phenomenonology of space. I hope that Gogel's approach or something like it may be valuable in demonstrating that many of the important phenomena dealt with by phenomenologists will in fact be taken care of by a quantitative type of approach. Because of Dr. Ogle's background and interests, I have no doubt that he will have a number of com- ments about this type of approach. Ogle: It is very true that I am interested in this approach to binocular space perception. Unfortunately, I haven't seen this development prior to this morning and I think it will take a great deal of study really to digest it. I don't feel that I am in a position either to commend or to critize at all, but I am glad to see more work being done in this field. I feel that the Lundburg theory has many de- ficiences7 one of which is that it has not taken into account the psychological, and even physiological, factors. If we do not take them in, I don't believe we will haste ~ wall -ro,~nA'?d nict'~r'? That' the ran son I'm very interested in Dr. Gogel's . . ~ ~ ~ ~ ~ of_ ~ ~ ~ hi_ ~ ~ hi_ ~ ~ ~ ~ ~ ~ ILL ~ ~ ~ V ~ ~ ~ ~ A J ~ ~ ~ v ~ approach here, but I am going to have to study it. Graham Dr. Ogle's point of view is one that I certainly subscribe to. I didn't mean to imply when I talked about Dr. Gogel's account that I subscribe to it, at least not before validation. However, I do agree with Dr. Ogle that it is important that researches and theories be developed to encompass much more than what has been considered the classical area of depth perception. Dr. Gogel's discussion attempts to do this. 139

Next: Session IV - New Techniques Under Development »
Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!