size-distance variance and eye accommodation: the ways of an investigator
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Size-Distance Variance and EyeAccommodation: The Ways ofan InvestigatorStanley N. RoscoePublished online: 13 Nov 2009.
To cite this article: Stanley N. Roscoe (1998) Size-Distance Variance and EyeAccommodation: The Ways of an Investigator, The International Journal of AviationPsychology, 8:1, 75-81, DOI: 10.1207/s15327108ijap0801_5
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THE INTERNATIONAL JOURNAL OF AVIATION PSYCHOLOGY, 8(1), 75-81 Copyright O 1998, Lawrence Erlbaum Associates, Inc.
RESEARCH NOTE
Size-Distance Variance and Eye Accommodation: The Ways of an
Investigator
Stanley N . Roscoe ILLIANA Aviation Sciences Limited
McKinleyville, CA, and Las Cruces, NM
Biased judgments of size and distance are encountered with all types of imaging displays, and the literature on visual perception is replete with violations of the size-distance invariance hypothesis, including the paradoxical moon illusion. To sort out the basic variables that relate these seemingly unrelated events calls for unfettered multifactor experimentation rather than the severe reduction of traditional psycho- physical methodology. The high correlation among the focal distance of the eyes, apparent size, and changes in the locus of the retinal blind spot would never have been discovered if all cues to distance other than accommodation had been eliminated, as called for by experimental reductionists.
All truth passes through three stages. First, it ir ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
-Arthur Schopenhauer
Much has been said and written on the distinction between basic and applied research: about how little of basic importance trickles down from applied experi- ments and how seldom basic research addresses practical real-world problems. When the latter occasionally does occur, the relations among interacting variables are typically so suppressed through experimental reduction that little of a gener- alizable nature is learned. Worse yet, reduction experiments often yield null results,
Requests for reprints should be sent to Stanley N. Roscoe, 2750 Sunny Grove Avenue, McKinley- ville, CA 95519.
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76 ROSCOE
allowing the investigator to "rule out7' the possibility that the original problem can be explained in terms of the manipulated variable.
Then, perhaps years later, the problem is revisited with multivariate experiments, and the variable is shown to have main effects and interactions that partially explain a long unsolved mystery. A prime example is the paradox surrounding the moon illusion (Hershenson, 1989) and the size-distance invariance hypothesis: the notion that "A retinal projection or visual angle of a given size determines a unique ratio of apparent size to apparent distance" (Kilpatrick & Ittleson, 1953, p. 224). Stated another way: For objects subtending the same visual angle, apparent size will vary directly with apparent distance.
Size-Distance Variance
The paradox is not in the hypothesis but rather in the results of experiments in which the predicted invariance is violated: in judgments under reduced viewing condi- tions, in the "projection" of afterimages, and-since long before the time of Ptolemy-in the paradoxical moon illusion. How can it be that myriad experiments in these ever-popular problem areas have failed to explain how our visual machinery mediates our perception of the size and distance and angular position of objects? Is it possible that our traditional psychophysical methods guarantee the suppression of the very effects we seek to reveal?
Research Strategy
The central factual issue in the discussion that follows involves the role of eye accommodation in the perception of size, distance, and angular position. The once prevailing strategy in perceptual research is stated by Hochberg (197 1): "Whether accommodation has any actual value as a depth or distance cue can only be determined by experiments in which all other cues of distance are excluded" (p. 47 8).
Such a statement disclaims the importance of interactions in normal viewing between eye accommodation and other visual and neural mechanisms. More specifically, it disclaims the possibility that the accommodation reflex, to perform an apparent-size-attenuating function, depends on textural cues to distance present in the everyday visual world. Nevertheless, Hochberg (1971) summarizes his review as follows: "Seventy years of research of this kind [reduction experiments] leave us with the conclusion that accommodation is, at best, a pretty weak cue to distance even at short distances" (p. 479).
However, facts belie Hochberg's (1971) conclusion, and it is now evident that accommodation is centrally involved in size arid distance perception (Benel,
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THE WAYS OF AN INVESTIGATOR 77
197911980; Hull, Gill, & Roscoe, 1982; Iavecchia, Iavecchia, & Roscoe, 1983, 1988; Roscoe, 1985, 1989; Simonelli, 1979). To establish this fact, multivariate experiments were needed in which eye accommodation was measured while observers were judging the sizes of objects as a function of the visibility, distribu- tion, and aspect angles of textured surfaces and gradients in the visual scene (Gibson, 1966, 197911986).
INVESTIGATION
A Real-World Problem
From the earliest use of closed-loop visual systems in airplanes and flight simula- tors, it was evident that airport runways and other surface features appeared smaller and farther away than they should (Roscoe, 195011951, 1984; Roscoe, Hasler, & Dougherty, 1966). Later it became evident that an apparent shrinkage of the visual field is common to all imaging systems that reduce cues to distance-microscopes, periscopes, "one power" shotgun scopes, and head-up and head-mounted virtual image displays. The apparent compression of a simulated airport scene causes the runway to appear higher than it should relative to the horizon, and hence the approach angle appears shallower and the distance to the aimpoint appears farther than they actually are. The result is a long, hard landing.
Reasonable Speculation
Despite the conclusion expressed by Hochberg (1971), many have speculated that the apparent shrinkage of objects in imaging displays is somehow associated with focal distance. Although convergence micropsia at short viewing distances has been demonstrated in countless experiments, biased judgments have been reported not only with real images at close distances but also with collimated images that do not induce convergence (Randle, Roscoe, & Petitt, 1980). Focal distance continues to vary in response to objects at distances well beyond the near limit of "optical infinity," and a search of the literature reveals many violations of the size-distance invariance hypothesis that would surely have been correlated with the observer's focal dis tanceif only it had been measured (Roscoe, 1977, 1984).
Many of the reduction experiments included some conditions with visible texture gradients that would have pulled the observer's focus outward from its tonic state or dark focus distance (Leibowitz, Hennessy, & Owens, 1975). The classic Holway and Boring (1941) experiment, "Determinants of Apparent Visual Size with Distance Variant," is a perfect example, one in which the effective stimuli for distant focus ranged from a visible texture gradient to virtual elimination. In those
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days, convenient optometers were not yet available, so the high correlation between focal distance and apparent size went undiscovered for another 35 years (Roscoe, 1977; Roscoe, Olzak, & Randle, 1976).
Establishing a Relationship
The magical year was 1970, the year Robert Hennessy reported his invention of the laser optometer, and he and other students of Herschel Leibowitz at Pennsylvania State University started measuring focusing responses under various laboratory conditions (Hennessy & Leibowitz, 1970). Concurrently, Tom Cornsweet and Hugh Crane were developing the Stanford Research Institute's focus stimulator and covert, servo-controlled infrared optometer for NASA's Ames Research Center (Cornsweet & Crane, 1970; Crane & Cornsweet, 1970).
Initially using the Cornsweet-Crane optometer at Ames Research Center, fol- lowed by a Hennessy laser optometer and a Simonelli (1980) polarized vernier optometer at the University of Illinois and New Mexico State University, my students, associates, and I conducted more than a dozen experiments in which mean apparent size correlated about 0.9 with mean focal distance over a wide range of viewing conditions for a variety of visual tasks. Only the first two experiments, done at Ames, were confined to the laboratory; the others all involved outdoor vistas, with some laboratory conditions as well, and more than half called for judgments of the apparent size of a collimated virtual "moon" combined with the visual scene (Roscoe, 1989).
Pursuing an Explanation
The fact that apparent size is highly correlated with focal distance is consistent with many violations of the size-distance invariance hypothesis. However, a correlation is a statement of a relation; it is not an explanation. To explain how the system works, the mechanisms it employs must be identified. We must discover what causes apparent size to increase with focal distance and, concomitantly, apparent distance to decrease; The horizon moon also looks nearer, not farther, as called for by the size-distance invariance hypothesis (Kaufman & Rock, 1962, 1989).
Reification of Assumptions
Reduction experiments often involve testable but untested assumptions, possibly ones that were untestable when originally made. Over the years, such assumptions become reified; They are mentally converted into something concrete or objective. One such assumption is embodied in the Kilpatrick and Ittleson (1953, p. 224) statement of the size-distance invariance hypothesis, namely, the interchangeabil- ity of the terms "retinal projection" and "visual angle." This assumption of an
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THE WAYS OF AN INVESTIGATOR 79
invariant relation between visual angle and effective retinal size has never been validated experimentally. Nonetheless the assumption is firmly embedded in mod- els of the reduced schematic eye.
POSSIBLE MECHANISMS
In 1976, I challenged the invariant-relation assumption and advanced a zoom-lens hypothesis at the annual meeting of the American Psychological Association in Washington (Roscoe, 1977). My notion was that refractive changes in the lens with inward and outward accommodation attenuate the effective size of the retinal image. With no training in physiological optics and no reasonable explanation of how this might be mediated, I was on thin ice and was not surprised by the reaction of the vision community (notably Marsh & Temme, 1990; Smith, Meehan, &Day, 1992).
The idea was first ridiculed, then violently opposed, and to date it most certainly has not been accepted as self-evident. However, although I am now persuaded that the zoom-lens hypothesis is at best a partial explanation and that neural signals to accommodate and proprioceptive feedback together play a central, scaling role in judgments of apparent size (Lockhead & Wolbarsht, 1989), I have not given up on the idea that the effective size of the retinal image changes with focus.
In an experiment done at New Mexico State University, Louis Corl, Don and Darlene Couchman, and I found that the apparent locus of the blind spot caused by the optic disk moves by large amounts and in the predicted direction with shifts in focus (Roscoe, 1989, pp. 50-51; 1993, pp. 226-227). The apparent size of the blind spot also changes by as much as 45% or more with similar percentage shifts in focal distance. Since then, these effects have been independently replicated by the late Dennis Holding and his student Jeffrey Schmidt (Holding & Schmidt, 1992) at the University of Louisville.
It is not evident how neural signals to accommodate or proprioceptive feedback from the ciliary muscle could cause the blind spot to appear to dilate and constrict and to move. However, these effects would occur if there were a change in the effective size of the retinal image. To produce a zoom-lens effect, somehow (a) a unique apparent size of an object would have to be selected from the blur circles as a function of the difference between the focal distance of the eyes and the actual distance of the object, and (b) all other apparent sizes in the blur circles would have to be suppressed at the retinal level, as happens when out-of-focus objects are viewed through artificial pupils (Roscoe, 1989, p. 50; 1993, p. 221).
RESEARCH: BASIC AND APPLIED
The beauty and joy of scientific inquiry lie in: (a) identifying a practical real-world problem such as pilots' misjudgments of size and distance with imaging displays; (b) analyzing the basic physical and physiological variables that might be involved,
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such as location, aspect, collimation, and other characteristics of visible texture gradients, vergence and focal distance of the eyes, neural signals to accommodate, and proprioceptive feedback; and (c) manipulating and measuring such variables in multifactor experiments, leading to testable hypotheses concerning the mecha- nisms involved. Research is basic to the extent that its results are generalizable to the explanation of everyday events.
REFERENCES
Benel, R. A. (197911980). Visual accommodation, the Mandelbaurn effect, and apparent size (Doctoral dissertation, University of Illinois at Urbana-Champaign, 1979). Dissertation Abstracts Interna- tional, 40(10B), 4055 (1980; University Microfilms No. 80-08974).
Cornsweet, T. N., & Crane, H. D. (1970). Servo-controlled infrared optometer. Journal of the Optical Society of America, 60, 548-554.
Crane, H. D., & Cornsweet, T. N. (1970). Ocular-focus stimulator. Journal o f the Optical Society of America, 60, 577.
Gibson, J. J. (1966). The senses considered as perceptual systems. Boston: Houghton Mifflin. Gibson, J. J. (1986). The ecological approach to visual perception. Hillsdale, NJ: Lawrence Erlbaum
Associates, Inc. (Original work published 1979) Hennessy, R. T., & Leibowitz, H. W. (1970). Subjective measurement of accommodation with laser
light. Journal of the Optical Society of America, 60, 170&1701. Hershenson, M. (Ed.). (1989). The moon illusion. Hillsdde, NJ: Lawrence Erlbaum Associates, Inc. Hochberg, J. (1971). Perception: 11. Space and movement. In J. Kling & L. Riggs (Eds.), Woodworth
andSchlosberg's experimentalpsychology (3rd ed., pp. 475-550). New York: Rinehart &Winston. Holding, D. H., & Schmidt, J. (1992, November). Accommodation and the blind spot. Paper presented
at the 33rd annual meeting of the Psychonornics Society, St. Louis, MO. Holway, A. H., &Boring, E. G. (1941). Determinants of apparent size with distance variant. Amencan
Journal of Psychology, 54,21-37. Hull, J. C., Gill, R. T., &Roscoe, S. N. (1982). Locus of the stimulus to visual accommodation: Where
in the world, or where in the eye? Human Factors, 24, 311-319. Iavecchia, J. H., Iavecchia, H. P., &Roscoe, S. N. (1983). The moon illusion revisited.Aviation, Space,
and Environmental Medicine, 54, 39-46. Iavecchia, J. H., Iavecchia, H. P., & Roscoe, S. N. (1988). Eye accommodation to head-up virtual images.
Human Factors, 30, 689-702. Kaufman, L., &Rock, I. (1962). The moon illusion. Scientific American, 207(7), 12&130. Kaufman, L., &Rock, I. (1989). The moon illusion thirty years later. In M. Hershenson (Ed.), The moon
illusion (pp. 193-234). Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Kilpatrick, F. P., & Ittleson, W. (1953). The size-distance invariance hypothesis. Psychological Review,
60, 223-231. Leibowitz, H. W., Hennessy, R. T., & Owens, D. A. (1975). The intermediate resting position of
accommodation and some implications for space perception. Psychologia, 18, 162-170. Lockhead, G. R., & Wolbarsht, M. L. (1989). The moon and other toys. In M. Hershenson (Ed.), The
moon illusion (pp. 259-266). Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Marsh, J. S., & Temme, L. A. (1990). Optical factors in judgments of size through an aperture. Human
Factors, 32, 109-1 18.
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by [
Flor
ida
Atla
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vers
ity]
at 1
8:58
15
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embe
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14
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Randle, R. J., Roscoe, S. N., & Petitt, J. (1980). Effects ofaccommodationandmagn~ication on aimpoint estimation in simulated landings with real and virtual image displays (Tech. Paper NASA-TP-1635). Washington, DC: National Aeronautics and Space Administration.
Roscoe, S. N. (195011951). Airplane pilotperformance as a function of the extent and magniJication of the visible horizon (Ph.D. dissertation in engineering psychology, University of Illinois at Urbana- Champaign, 1950). Dissertation Abstracts International, 11, 173 (1951).
Roscoe, S. N. (1977). How big the moon, how fat the eye? (Tech. Report ARL77-91AFOSR-77-8). Savoy, IL: University of Illinois at Urbana-Champaign.
Roscoe, S. N. (1984). Judgments of size and distance with imaging displays. Human Factors, 26, 617-629.
Roscoe, S. N. (1985). Aviation psychology. Ames, IA: Iowa State University Press. Roscoe, S. N. (1989). The zoom-lens hypothesis. InM. Hershenson (Ed.), The moon illusion (pp. 31-57).
Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Roscoe, S. N. (1993). Visual orientation: Facts and hypotheses. The International Journal ofAviation
Psychology, 3,221-229. Roscoe, S. N., Hasler, S. G., & Dougherty, D. J. (1966). Flight by periscope: Making takeoffs and
landings; the influence of image magnification, practice, and various conditions of flight. Human Factors, 8, 13-40. (Originally issued as Office of Naval Research Human Engineering Report 71-16-9, 1952; declassified in 1963)
Roscoe, S. N., Olzak, L. A., & Randle, R. J. (1976). Ground-referenced visual orientation with imaging displays: Monocular versus binocular accommodation and judgments of relative size. Proceedings of the AGARD Conference on Visual Presentation of Cockpit Information (pp. A5.1-A5.9). Neuilly-sur-Seine, France: North Atlantic Treaty Organization.
Simonelli, N. M. (1979). Apparent size and visual accommodation under day and night conditions. Proceedings of the Human Factors Society 23rdAnnual Meeting (pp. 374-378). Santa Monica, CA: Human Factors and Ergonomics Society.
Simonelli, N. A. (1980). Polarized vernier optometer. Behavioral Research Methods and Instrumenta- tion 12, 293-296.
Smith, G., Meehan, J. W., & Day, R. H. (1992). The effect of accommodation on retinal image size. Human Factors, 34,289-301.
Manuscript first received March 1997
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