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INTRODUCTION J. W. GEBHARD, The John Hopkins University Applied Physics Laboratory Despite the mutterings occasionally heard about how automatic signal detection and evaluation devices are putting the eye out of business, one observes little diminution in the use of visual displays of all kinds in current and projected military and civilian control systems. The instrumentation of aircraft cockpits, combat information centers, ground surveillance systems, arid air traffic con- trol towers is still being designed about the human eye. Indeed, as long as the brain of man retains its adaptability, and the sensitivity of the eye is about 6 db above that of the theoretically perfect detector, there appears to be an assured role for the visual display. ~ ( One of the most versatile kinds of display is the cathode-ray tube, which has proved so important in radar and sonar work. It was just ten years ago that Soller, Starr, and Valley, of the Massachusetts Institute of Technology Radiation Laboratory, so admirably described the research and development work on cathode-ray-tube displays that came out of World War II.1 Two years later Lawson and Uhlenbeck, in another volume of the MIT series, offered a systematic treatment of the detection of threshold signals.) Soon afterward, the large amount of human factors work on radar scopes that had accumulated was published without critical comment by Baker and Thornton.3 This useful compendium, unfortunately, is classified, although it largely contains data that are now un- classified. While many of the old difficulties remain with us, the operational requirements of most systems have changed with the world, and display prob- lems are not quite the same today as they were ten years ago. The time has come to determine once again what is required of radar and sonar displays, and how visual needs in particular are being met by the technical developments of recent years. It is most fitting that the Committee on Vision should undertake to do this, arid the Symposium on the Illumination and Visibility of Radar and Sonar Displays, reported herein, is a welcome start in this direction. The Symposium was open, which was doubtless the proper way to begin. It is to be expected, however, that some of the more important research and development in visual displays will have applications to national defense and, therefore, will be classified. A complete appraisal must consider this work also, and it is hoped that the Vision Committee will not limit its interest to the open material. Present surveillance systems utilizing cathode-ray-tube displays have changed more by making familiar requirements harder to meet than by intro iSoller, T., Starr, M. A., and Valley, G. E. Cathode-ray-tube displays. Massachusetts Institute of Technology, Radiation Laboratory Series, Volume 22. McGraw-Hill, 1948. ~Lawson, J. L. and Uhlenbeck, G. E. Threshold signals. Massachusetts Institute of Technology, Radiation Laboratory Series, Volume 24. McGraw-Hill, 1950. 3Baker, C. PI. and Thornton, G. B. Guide to factors affecting radar operators' efficiency. Defence Research Board, Department of National Defence, Canada, 1953, DMRL Report No. 84.

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ducing new ones. For examples the necessity for surveying much larger blocks of space than was once the case is the perennial range problem. We need also to find increasingly smaller objects in the presence of increasingly greater noise. Noise has always been on our cathode-ray tubes in a self-generated form. The art of countermeasures now makes noise a weapon against the display itself. No one has ever complained of having too much time in which to use a display, yet the time to detect and identify signals continues to shrink. The inevitable result of such considerations has been the development of much new equip- ment, from new radars and sonars to new display methods. No attempt can be made here to trace the many ramifications of this complex field. The most that can be done is to mention some of the display problems that relate most closely to the science of vision. The first problem is the visibility of threshold signals on cathode-ray tubes. This is much-plowed ground, but the old work does not help us greatly in pre- dicting the visual efficiency of new tubes and new phosphors, or in knowing what to expect of new developments in the presence of noise due to electronic jamming. The advent of storage tubes imposes the requirement that we learn how to assess and use these rather unconventional displays. The development of automatic signal detection systems challenges the superiority of the eye where it has always been supreme- in sensitivity. Under what conditions is the eye better than the machine? Are there target-enhancement schemes in which the eye can play a part? A second problem is the identification of signals. Here the eye is confronted by the ear as well as the machine. The possibilities contained in the aural identi- fication of radar signals have been explored by Licklider4 with generally fa,ror- able results, and the machine may be expected to perform a spectrographic analysis on the signal. Can the information contained in electrical signals also be presented for visual identification with any hope of success? Which of these systems can operate best in the noisy environment? A third problem concerns the use of displays for functions other than detec- tion and identification, for example, controlling and decision making. Ten years ago the inputs to visual displays came directly from the radar and sonar receivers. Familiar control functions such as tracking are still of interest, but we now frequently see secondary displays of data that are generated by computing sys- tems. These new displays have properties and uses that are quite different from conventional presentations. They are intense; noise is usually not a problem; they may be generated continuously; all sorts of symbols may be written on them; signals may be enhanced, suppressed, coded; and a flick of the switch can change their inputs. Some of the perceptual problems encountered in such displays are anticipated in the Vision Committee's Symposium on Form Dis 4Licklider, J. C. R. Studies in aural presentation of information. Operational A pplications Laboratory, Air Force Cambridge Research Center, Air Research and Development Command, Tech. Report No. AFCRC-58-53, 1957. -2-

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crimination, but too little is known of the other visual requirements for the design and use of these special-purpose displays. :Finally, there is the problem of using cathode-ray tubes in environments where the visual requirements imposed by the scopes are at variance with those of other visual tasks. Much has been accomplished by the specialized lighting of work places, and by the development of tube types that may be used in daylight. Nevertheless7 the difficult job of reconciling incompatible demands on vision has been handled largely on an ad hoc basis that has produced few general principles. Perhaps this kind of solution to a particular lighting problem is the only one, vet it would seem that a more generalized method, such as Blackwell suggests for interior lighting, might be used here too. The challenge afforded by a complete technical analysis of the visual re- quirements of visual displays is big perhaps dismayingly so if one remembers that the cathode-ray tube is only one of the many types of visual display. Never- theless, the reward will equal the challenge since the eye still remains the most important avenue of getting complex information into the observer's brain. - 5Wulfeck, J. W. ancl Taylor, J. H., (Eds.) Form discriminatic~n as related to military problems. Armed Forces-NRC Committee on Vision, National Academy of Sciences-National Research Council, 1957, Pub. No. 561.