The Role of Location Processing in the Perception of the Environment

;:;Volutionary consi.derations, anomalies i.n visual perception, and physiological and anatomical data provide support for the two-visual system hypothesis. In addition to the welldocumented contour-processing system, there is also a largely independent location processing system that codes size, motion, number, and texture, as well as locus. This system appears to be flexible, parallel, high in capacity and unobtrusive in its operation. It is essentially analog, reflecting its suitability for the guidance of locomotion over a continuously varying terrain. A caution is raised concerning the excessive reliance on slides, on verbal report, and on concepts based solely on alphanumeric data. The purpose of this paper is to provide some cautions and some guidelines for students of visual perception working at the psychology/ environment interface. More specifically, this paper deals with recent developments that have led to a broadened conception of the processing of visual information, a critical link in how man perceives and thinks about his environment. A pivotal concept in the modern psychology of perception is that of contour. Sharp edges, borders, and lines are prominent features of the visual world. Further, there is considerable evidence that single cells in the visual cortex respond to different kinds of contour information (Hubel & Wiesel, 1962). For example, some cells may be most sensitive to horizontal lines, some to lines at a 45 angle, and so on. Based on the pervasiveness of contour and the evidence for a physiological mechanism that codes contour into the activity of conveniently discrete elements, it is hardly surprising that some psychologists have concluded that the perception of contour is visual perception (e.g., cf. Thompson, 1969): There are, however, a number of grounds for doubting this identity. First, there is the perspective provided by evolutionary considerations. Many of the aspects of the visual world that appear most essential to survival in a difficult and dangerous world seem quite far removed from contour. Secondly, there are a number of phenomena of visual perception that appear to be analog in nature, and are difficult to interpret along the essentially digital lines of the contour processing system. The evolutionary perspective, although not widely held among psychologists, is not unfamiliar to students of psychology and environment (e.g., Shepard, 1966; Sommer, 1969; Hall, 1966; CarrOll, 1970; Griffin, 1969). In considering the sorts of visual stimuli important to survival, it is useful to remember that at one point in man's prehistory his line was probably represented by a small, grounddwelling undifferentiated mammal (Diamond & Hall, 1969). For such an animal, locus would seem to be of the greatest importance. Motion, that is, a change in lOCUS, appears to be another essential kind of stimulus information. Stimuli that move demand immediate attention. Besides motion in a plane, motion toward, called looming by Gibson (1969), and motion away appear critical. What one does with respect to a moving stimUlus is, in turn, largely a function of size. Additional information a small animal might find helpful includes some rough indication of form and a notion of how many objects are present. Finally, texture, as the most general and pervasive guide to depth (Gibson, 1946), would be a useful addition to any animal concerned with making his way over uneven terrain. As with the evolutionary considerations, several perceptual phenomena are also difficult to handle on the basis of contour alone. Figural aftereffects provide a striking example of a distortion of locus without a corresponding distortion of the figures in question. For example, after prolonged inspection of a pattern made of two adjacent squares and two distant squares, a pattern of four evenly spaced squares appears askew. The squares on the same side as the close together inspection squares appear far apart; likewise the squares on the side of the far apart inspection squares appear close together (Kohler & Wallach, 1944). The squares in this example tend to retain their crisp contours; the primary distortion is one of locus.