A two-process theory of the response to size and distance.

Abstract

Evidence for a two-process theory of the observer’s visual judgment of size and distance is summarized and evaluated. The primary process, as expressed by the size-distance invariance hypothesis (SDIH), concerns the interrelation of perceived size (S’) and perceived distance (D’), independent of information derived from memory or suggestion. The secondary process involves information regarding size (from memory or suggestion) not contained in the immediate visual stimulus. If the primary and secondary sources of size information differ, the object is seen as off-sized. This off-sized perception can be used to modify the direct report of the distance of the object. In the case of the casual suggestion of size, the off-sized judgment produces a nonperceptual (cognitive) report of distance (Gogel, 1981b). In the case of the memory of the size of a familiar object, some of the effect on the direct report of perceived distance is perceptual, but most is cognitive (Gogel, 1976). In the case of optical expansion, the effect of off-sized judgments on distance responses produces a clear modification of perceived distance (Swanston & Gogel, 1986). The experimental distinction between primary and secondary processes is facilitated by comparing measures of perceived distance obtained from direct procedures (e.g., verbal reports of distance) with those obtained from indirect procedures (e.g., the head motion procedure). The former (direct) methods reflect both primary and secondary sources of information. The latter (indirect) methods are sensitive only to primary sources. The significance of the two-process theory for the specification of the SDIH and the explanation of other visual phenomena is discussed.