Behavioral and Social Science 50 Years of Discovery (1986) / Chapter Skim
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Visual Perception of Real and Represented Objects and Events
Visual Perception of Real and Represented Objects and Events
Pages 249-298
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From page 249... ...
The problems of perception continue to engage all the disciplines already mentioned; in addition, computer science is now a major presence in the field, providing tools and motivation in several distinct but closely related ways: as a source of techniques for research, theory testing, and modeling; as a source of analogies and metaphors; as an overlapping enterprise, seeking to devise machines that will "perceive" in the same way that people do; and in the context of learning how to generate and display computer images that humans can readily and accurately comprehend.
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A: One of the optical aids that artists have used for centuries (surer) to help in preparing a surrogate that provides the eye with much of the same stimulus information as the object or scene being represented.
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depth cues: the tracing of the scene in Figure 1B. ~ Linear Perspective: paral- 3 ~ 19px 8 , let lines ~8, 7-9, etc., ~ ~ TIC >\ converge in the picture f ' l.
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It is instead a strong clue about our sensory nervous systems, and it provided the background for the classical theory of perception and the nervous system, which we consider next. PSYCHOLOGY AND PHYSIOLOGY FROM 1850-1950 Given the facts of color mixture, the most parsimonious model of visual perception was the Young-Helmholtz theory (Helmholtz, 18661: that color perception is mediated by three kinds of specialized receptor neurons, the cones, each responsive to most of the spectrum, but each with a different sensitivity function.
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From page 253... ...
Such information as the limits of resolution and the bases and specification of colors provided the first goals for what has become visual science and its applications, which now run from the prescription of spectacles to the design of television characteristics. It was also the foundation of the classical view of the perceptual process in general, diagrammed in Figure 6: at left, the object in the world, with its physical properties of distance, size, shape, reflectance (surface color)
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SPACE ETC. FIGURE 6 The classical theory (1850-1950~.
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From page 255... ...
These packets of sensations normally come in characteristic patterns that are imposed by the regularities of the physical world, patterns such as the depth cues in Figure 2. By learning these regularities and their meanings, we learn to perceive the physical world and its properties.
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Nevertheless, we tend to perceive such object properties correctly, despite changing retinal stimulation. The classical theory held that this object constancy, as it is now known, is achieved when the viewer takes
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This explanation is now commonly called "unconscious inference." Its operation assumes that the viewer has learned the constraints in the physical world (e.g., that L= R x E, that S =kDtanD, etch. These constraints, once learned, provide a mental structure that mirrors the physical relationship between the attributes of the object and those of sensory stimulation, permitting the viewer to infer or compute the former from the latter.
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From page 258... ...
As we will see, Helmholtz was right about the three cones and in some sense about the existence of mental structure and computation. But most of the rest of what lay between those points was wrong, and most of the alternative proposals that had been made by the critics of that dominant approach, especially those of Hering and Mach, were quite remarkably vindicated within a period of a very few years, after having been largely ignored for many decades.
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Cells farther in the nervous system are sensitive to a bar of specific orientation moving in a specific direction 5. trum by determining how much of each pure hue was needed to cancel all traces of its opponent.
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With respect to their possible perceptual functions, such pattern-sensitive networks open the way to very different kinds of explanation of the perceptual process. One of these is that the visual stimulus is analyzed into fundamental elements that do a great deal of what had been considered the task of learning and of unconscious inference.
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From page 261... ...
Spatially organized and extended neural structures are exemplified in a third class of alternatives that is based on the following idea of spatialfrequency channels: A sine-wave grating is a set of dark and light bars in which the intensity of the light varies in a sine wave. The width of the bars in such a grating defines its spatial frequency (i.e., the number of bars or cycles per degree of visual angle)
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From page 262... ...
For example, the frog's retina contains cells that respond not to the intensity of light in some part of the retinal image, but to the ratio of intensities of surrounded and surrounding regions (Campbell et al., 19781. As has been realized since Hering and even Helmholtz, that ratio remains invariant regardless of changes in illumination as long as both regions are equally illuminated so that as sketched in Figure 10 equal ratios of luminance in the proximal stimulation (P.S.)
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From page 263... ...
and remains an influential approach today. The most sweeping and radical proposal of this kind is a direct theory for allofperception(Gibson, 1966, 1979~:0ur nervous systems"resonate" to stimulus properties that remain invariant when the light at the eye undergoes transformations (e.g., the optical flow patterns and motion parallax, Figure 1 1)
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Gibson (1951, 1966) has emphasized several ways in which the changing pattern of light to the moving observer, such as the optical expansion patterns in C, provide potentially usable information about spatial layout and offer invar~ants that, if responded to directly, might explain the perception of distal object properties.
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From page 265... ...
The Evidence for Perceptual Rules Rather Than Lookup Tables It is easy to see how learning by association might invest specific patterns of stimulation with specific perceptual meanings, and to speculate about a neurophysiological basis for such associative learning, but it is harder to be specific about a learning process through which abstract rules might be learned. (This is the distinction, made earlier, between '`lookup tables" and an inference or computational process that solves some internalized formula)
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(C,D) By the minimum principle that we see the simplest organization-(C)
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The Promise of a Minimum Principle To make the insights of Gestalt psychology scientifically or practically useful we need either a great deal of quantitative and object measurement of the strengths of the different rules, along with an appropriate combinatorial principle, or some equally quantitative and objective overarching rule that supplants the set of individual rules. For the latter purpose Gestalt psychologists offered a minimum principle, i.e., that we perceive the simplest organization the simplest alternative object or arrangement-that fits the stimulus pattern (Koffka, 19351.
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(We will return to this point shortly.) With respect to the minimum principle, Figure 12E is completely incompatible with any rule based on the entire object.
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The differential motions within the stimulus pattern offered by the scene provide the moving observer with rich information about the structure of the world. A critical question being explored today is how much of that information is used, and in what form.
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Since then the dissemination of relatively cheap 16-millimeter motion picture cameras capable of producing controlled motion through animation, the advent of even cheaper and more convenient video equipment, and, above all, the availability of computer-generated displays, have progressively revolutionized the study of patterns that change with time. We are now in the midst of an explosion of research on the topic, done as much by computer scientists, physicists, and neurophysiologists as by perceptual psychologists.
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271 D Lit" \ .
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From page 272... ...
Moreover, it includes the perception of motion pictures, and the phenomena represented in Figures 13 Trough 15, under the same general explanation. As computers have made it easier to generate pictures of points moving in space, and as more research is done with such patterns, the point first made by the Gestalt demonstrations that perception is governed by rules rather than lookup tables has taken hold.
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But if that effort is to apply to human perception, it must start with perceptual rules that indeed are used in the human perceptual process. We still must decide what those rules are.
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there is no experimental support for such an explanation of the phenomenon; indeed, there are features of He changing retinal image that might be direct, if misleading, bases of the illusory response (Braunstein, 1976; Hochberg, 1984b)
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Even when the changes provided by the moving object are clearly above the detection threshold and the illusion is therefore accompanied by clearly perceived nonrigidities, the latter is what we see, and not the veridical rigid motion (Hochberg, 1984b; Hochberg et al., 19841. Subtle arguments are not needed, however: Given the lessons of Figure 16, we can readily devise new illusions in which rigid simply moving objects, freely viewed (with monocular vision)
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Human perceptual functions here serve only as "existence" proofs that assure the computer scientist that at least one way of solving the problem exists and is embodied in human neuroanatomy. Once we start to consider the means by which modern electronic com
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That may turn out to be the most important relationship of all between computer science and perceptual psychology, and we consider that next. The Computer as an Analogy to Perception Perhaps the greatest effect of the computer has been its influence as an analogy: Inherently vulnerable to entrapment in the mind-body problem of philosophers and metaphysicists, and self-conscious about the need to be scientific, psychology is always tempted to confine its attentions to variables that are conceived and measured in physical terms.
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The point is worth spelling out in a brief examination of the field. Because it is far easier to make initial progress at formulating specific models of direct neural response to stimulus information than at formulating specific models of central processes of learning and inference, most of the work in this field has concentrated on the former (see Haber, 19831.
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Regardless of the intrinsic merits of computer simulation and of the quest for perceiving machines, and without appeals to metatheory or philosophy of science, there remains a present and growing need to develop theories of human perception to the point that they can be embodied in computer programs. That is the relationship between the computer and perceptual psychology that we consider next.
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From page 281... ...
But we have seen that even perfect fidelity i.e., the moving object itself may result in misperceptions (Figures 16, 17~. The constraints on mental structure-on the structure of perceived objects are not the same as the normal constraints on physical objects, and we must know the former as well as the latter if we are to be able to predict how pictures are perceived, even with the best picture quality possible.
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, but terms or even models are not needed here so much as facts, and more attention paid to what facts we do have. We next consider very briefly the current state of research on mental structure in real and represented objects.
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or to invariant stimulus information. The perception of a single object rather than of separate fragments often depends on the viewer's having specific knowledge of what that object normally looks like, and on being ready to perceive it.
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Moreover, as we have discussed at length, the last 30 years have also shown that much of perceptual structure may be given directly by complex neurophysiological circuitry; if that is at all true, such prewired perceptual structure must surely affect the nature and use of whatever mental structure does exist in addition. For example, for all we know at present the Ames trapezoid phenomenon (Figure 16)
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From page 285... ...
The perception of objects that are partially obscured in normally cluttered environments must often draw on a process of fitting fragmentary sensory information into a previously provided mental structure (Figure 191. In addition, our perceptions of any scene or moderately large object must be assembed over time by means of successive glances, each of which provides only a partial view of the world.
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. And both functions suggest methods by which mental structure may be studied.
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If the motions are not visible, as they are not in this experiment, then the sequence of static views is indecipherable and in fact cannot be kept in mind; if a long shot of the object is presented first, however (as in row B) , providing a mental structure within which the successive views can take their place, the subject can again perceive the object that is moving behind the aperture (Hochberg, 1978a)
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in Figure 21A. It implies a usable and consistent relationship between time and distance in a mental structure that cannot be attributed to physical stimulus information.
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From page 289... ...
increases with angle, ¢, between their orientations, as above. But if the comparison figure is presented after an interval t = ¢/m, where ~ is the subject's characteristic rotation rate (obtained from the slope of the function at t = 0.0)
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From page 290... ...
controls are needed, the preliminary results will, I feel certain, survive the necessary replication and controls: Orthographic and isometric projections can both specify the form of a three-dimensional object, but the isometric projections are in some sense closer to the way in which we extract and store the information-closer to the mental structure involved in perceiving and comparing the objects. Although I know of no research to the point, it hardly needs an experiment to discover that isometric pictures are more rapidly and accurately comprehended than orthographic ones.
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Journal of Experimental Psychology: Human Perception and Performance 7:241-274.
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From page 292... ...
1983 Four assumptions about invariance in perception. Journal of Experimental Psychology: Human Perception and Performance 9:310-317.
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Haber, R.N. 1983 Stimulus information and processing mechanisms in visual space perception.
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New York: Appleton-Century-Crofts. 1978a Motion Pictures of Mental Structures.
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I Journal of the Optical Society ofAmerica 51:422-429.
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1983 Opposed-set measurement procedure: a quantitative analysis of the role of local eues and intention in form perception. Journal of Experimental Psychology: Human Perception and Performance 9:183-193.
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1983 Perception of surface curvature and direction of illumination from patterns of shading. Journal of Experimental Psychology: Human Perception and Performance 9:583-595.
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From page 298... ...
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