Night Vision Current Research and Future Directions, Symposium Proceedings (1987) / Chapter Skim
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Human Performance Issues
Human Performance Issues
Pages 235-302
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From page 237... ...
However, from his assessment he took a rather dim view of night vision testing, and I quote some of his conclusions (Berry, 1949~: One generalization is unfortunately that tests of night vision are not very reliable. Visual acuity, contrast sensitivity, absolute sensitivity etc.
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From page 238... ...
My experience exemplifies night vision testing over the years. Regularly the necessity for night vision testing was disparaged r as each new electronic aid or superior sensing system emerged.
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From page 239... ...
S . 1962 Review of literature on night vision testing.
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From page 240... ...
has correctly noted that the term visual search appears as a loose label for a variety of phenomena and experimental paradigms that certainly do not share a common denominator. In this summary I will follow Monk's suggestion to limit the discussion to situations that are characterized by "spatial uncertainty reduction and target uncertainty to a greater or lesser extent" (Monk, 1984, p.
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From page 241... ...
On the other extreme there are free search conditions usually characterized by analysis of eye movements. The first type of experiment starts from the reasonable assumption that visual search is guided by the limiting conditions of the visual system, and in particular by the properties of peripheral vision.
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From page 242... ...
The most relevant question with regard to visual search is related to the determination of the next fixation during the preceding one. The excellent accuracy in aiming at the next fixation, together with the limited saccadic movement times -- about 100 ms for a 40-degree movement (e.g., Sanders, 1963 -- render a closed-loop explanation of saccadic eye movements quite unlikely.
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From page 243... ...
This starts with visual acuity prof lies of the common Landolt ring type in conditions without either temporal or spatial uncertainty, which is then extended to conditions with spatial uncertainty (e.g., Michon and Kirk, 1962a; Corbin et al., 1958~. Recent research in this direction concerns covert orientation of attention, which has shown convincing evidence that visual attention can be shifted to a position other than the line of sight.
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From page 244... ...
Yet, it should be fully clear that these considerations are at best a small part of the visual search story. One of the main limitations is that the work discussed so far is concerned with a largely empty visual field, while, as mentioned above, more structured visual displays are more common.
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From page 245... ...
and turn out to be the most powerful cue in visual search. It should be noted, though, that to be effective, the targets should always have the same color.
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From page 246... ...
Yet, the really strategic factors in visual search have' usually been related to more or less cognitive scanning patterns and their changes as related to environmental and organismic factors. A convenient starting point for this discussion is the work on inspection strategies of a lime ited number of displays, as initiated by Senders (1964, 1967, 198~)
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From page 247... ...
In addition, Moray (1984) describes various models that add elements of decision making by assuming that there are costs for each observation and missed signal an~a benefits for each correctly detected signal in determining the critical value of the interval between successive f fixations.
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From page 248... ...
It is probably fair to say that the microstructure of scan paths is probably quite auto~natic -- like in the succession of f ixations and saccades in reading -- while the microstructure, e.g., biasing certain areas of the visual f ield, is more under cognitive control. So far little is known about the actual interrelations between automatic and controlled aspects of visual search and about the conditions under which either mode predominates.
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From page 249... ...
There is a clear need to investigate more systematically strategic effects on visual search and scanning, including measures that go beyond the most simple performance measures of time and signal detection.
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From page 250... ...
Although the display constraints are known to interact with topdown type of visual search strategies, which are liable to effects of fatigue and stress, little is known either about the more precise relations between strategies and display constraints or about the set of possible search strategies that are actually used. The most pressing research needs in the field of visual search seem to center around these interactions.
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From page 251... ...
Bouma, H 1978 Visual search and reading: Eye movements and functional visual field: A tutorial review.
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From page 252... ...
Bellamy 1979 Eye movements and visual search.
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From page 253... ...
American Journal of Psychology 80:1-13. 1984 The control of attention in visual search.
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From page 254... ...
Vaughan, J., and T.M. Graefe 1977 Delay of stimulus presentation after the saccade in visual search.
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From page 255... ...
255 Yarbu s, A .L . 1967 Eye movements and vision.
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From page 256... ...
It is therefore interesting to compare the functional properties of foveal and peripheral vision and to evaluate their significance for different visual tasks. This paper will provide an overview of selected peripheral visual functions (detection sensitivity, visual acuity, spatial and temporal summation, spatial and temporal contrast sensitivity, and motion sensitivity)
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From page 257... ...
Because other visual functions in the periphery also display these large inter- and intraindividual differences, they may represent an important factor in predicting performance skills for tasks that depend on peripheral vision. Visual acuity at photopic luminance levels exhibits an approximately linear decrease from the fovea out to the periphery, when the data are plotted according to the log minimum angle of resolution (Kerr, 1971; Johnson et al., 1978~.
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From page 258... ...
I ~ I , I ~ 0 10 20 30 Visuel Field Eccentricity (deg.) FIGURE 2 Peripheral visual acuity measurements obtained by seven different investigators.
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From page 259... ...
The resolution cutoffs (visual field locations corresponding to the resolution threshold at maximum stimulus luminance) are consistent with peripheral visual acuity measurements using conventional acuity measurement techniques, as indicated by the curve labeled "Present Results" in Figure 2.
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From page 260... ...
and acuity (resolution sensitivity) profiles of the visual field for 10', 17', 26', 42', and 66' target sizes at photopic background luminances.
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prof lies of the visual f ield for 10' target size at 5 different background luminances.
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From page 262... ...
prof lies of the visual f ield for a 17' target size at S cliff erent bac Aground luminance s.
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From page 263... ...
c ~ 1.0 _ 9 2.0 Go I in I -3.0 -1.0 0.0 1.0 2.0 26' (20/80) Target S T AT I C P R O F I L E a' __ Background Luminance ~~ ~ 3.18cd/m2 C 0 0.32 cd/m2 0.032 cd/m2 0.0032 cd/m2 · · 0.00032 cd/m2 ACUITY PROFILE loo , , 30 20 10 0 10 20 30 -- -- - -- Nasal VISUAL FIELD ECCENTRICITY(Deg)
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From page 264... ...
However, these features appear on the resolution sensitivity profiles at background luminances that are about 1 log unit lower than their occurrence on the detection sensitivity profiles. A similar pattern can be observed for the 66 min arc (20/200)
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From page 265... ...
prof lies of the visual f ield for a 42' target size at 5 dif ferent background luminances.
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From page 266... ...
profiles of the visual field for a 66' target size at 5 different background luminances.
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From page 267... ...
At all visual f ield locations, motion sensitivity at scotopic background levels was poorer than for photopic backs round luminances. There was a smaller effect of luminance on peripheral motion thresholds than for the fovea; this is similar to the results reported for peripheral visual acuity and background luminance.
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From page 268... ...
. A related phenomenon has been reported by a number of authors for slowly moving objects in the peripheral visual field (Campbell and Maffei, 1979, 1981; Cohen, 1965; Day, 1973; Enoch et al., 1976; Hunzelmann and Spillman, 1984; MacKay, 1982; Tynan and Sekuler, 1982~.
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From page 269... ...
The influence of these perceptual phenomena on other visual skills such as judgments of distance, visual search, vigilance, and related performance tasks is not known at present. Further research is needed to understand these perceptual effects in the peripheral visual fields and their relationship to performance of tasks that rely on peripheral vision.
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From page 270... ...
RECOMMENDED INSTRUMENTAT I ON One desirable clinical instrument for a night vision laboratory is an automated perimeter. For screening of peripheral vision to detect ocular or necrologic disorders, an automated suprathreshold static perimeter would be sufficient.
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From page 271... ...
Detection sensitivity, resolution sensitivity, flicker sensitivity, spatial summation, temporal summation, dark adaptation, and glare sensitivity can all be evaluated with the TObinger perimeter at any location in the visual field. Background luminances f rom low-photopic to scotopic (a 6-log-unit range)
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Dunn, P.M., and R.W. Massof 1983 Temporal resolution in the peripheral visual field.
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From page 273... ...
Sloan 1947 Peripheral visual acuity. American Journal of Ophthalmology 30:581-588.
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From page 274... ...
Journal of the Optical Society of America 84:887-88y. Scobey, R.F., and C.A.
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From page 275... ...
. In contrast, relatively little is known about the visual performance capabilities of older adults at night.
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From page 276... ...
s FIGURE 1 Pupil diameter in millimeters (ordinate) as a function of age.
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From page 277... ...
8 7 6 s 4 3 hi, ~0 O ~IO 15 20 25 30 35 90 95 50 S5 60 t5 70 75 tO 85 tO FIGURE 2 Pupil diameter in darkness as a function of age for 1,263 sub jects. Note the wide individual variability.
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From page 278... ...
Dark Adaptation Dark adaptation has historically been one of the most popular topics of interest to researchers of aging and vision. Most of the studies presented in the literature are rather old, but they are quite numerous and for the most part well executed (e.g., Robertson and Yudkin, 1944; Steven, 1946; Birren et al., 1948; Birren and Shock,
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From page 279... ...
There is also a highly signif icant correlation between age and threshold at each point dur ing the dark adaptation process, i .e., older adults tend to have higher thresholds at each time interval tested . These curves ind icate that target luminance must be doubled every 13 years to be seen by the dark-adapted eye throughout life (Pitts, 1982)
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From page 280... ...
. Acuity One of the most common clinical measures of visual function is acuity, the smallest visual detail that an observer can resolve.
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From page 281... ...
All age groups had reduced acuity at the lower luminance level, but older adults, particularly those in their 70s and Bus, seemed to have greater acuity reductions relative to those of young adults at the lower luminance. In fact, their acuity was so poor that it was worse than that at the largest target size presented in the study.
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282 1~= o 20 Ho 60 80 loo TEST LETTER CONTRAST (%)
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. DI RECTI ONS FOR FETUS RESEARCH I t should be fairly obvious from this review that there is a clear need for more psychophysical research on aging and night vision.
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From page 285... ...
Campbell, F.W., and A.H. Gregory 1960 Effect of size of pupil on visual acuity.
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From page 286... ...
McFarland, R.A., and R.G. Domey 1958 Exper imental studies of night vision as a function of age and changes in illumination.
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From page 287... ...
1977 Effects of luminance and contrast on visual acuity, ages 16 to 90 years. American Journal of Optometry and Physiological Optics 54:178-184 .
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From page 288... ...
THE ROLE OF VI SI ON MODELS IN HUMAN E ACTORS Andrew B Watson Other authors of papers in this volume have described some of the facts of night vision and some of the outstanding questions in that area.
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From page 289... ...
289 data evaluaLion~ ~ ; .
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From page 290... ...
2. Temporal contrast sensitivity*
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From page 291... ...
291 leap for human factors. Although this goal has not been reached, some progress has been made; some examples are given below.
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From page 292... ...
Finally, the gain of each sensor is set by an overall contrast sensitivity function that is unique to each observer. With this simple structure it has been found that many of the outstanding features of spatial sensitivity and discrimination can be explained.
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From page 293... ...
FIGURE 4 Receptive f ield weighting function of a spatial sensor and its f requency spectrum. evaluation of the legibility of alphabetic fonts, or~ more generally, the discriminability of arbitrary sets of visual symbols.
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From page 294... ...
A NOTE ON TOOLS One of the purposes of the papers presented in this volume is to give suggestions for the design of a night vision laboratory. Since I am promoting the notion of model and theory as an integral part of such a laboratory, the question arises as to what tools will best serve the vision theorist.
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From page 297... ...
Robson, J 1966 Spatial and temporal contrast sensitivity functions of the visual system.
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From page 298... ...
Journal of the Optical Society of America A 3 (3)
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From page 299... ...
Some of you may not be aware that there were dozens of tests of night vision developed during World War II. Referring back to my introductory remarks concerning my reviews of the early literature on night vision testing, two points stand out in my mind.
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From page 300... ...
Spatial uncertainty in terms of automated visual field testing has been developed and is used quite widely. By implementing modest alterations to these test procedures, appropriate night visual search tasks or related tests incorporating spatial uncertainty could be readily accomplished.
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From page 301... ...
But even in the younger population there are large individual differences. I certainly feel that these individual differences in the normal population should be investigated, especially with regard to task performance and the effects of practice and training.
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