The Perceived size of visual objects defined by texture boundaries

Abstract

In a study of whether textural contours evoke the illusion of size, psychophysical experiments were carried out with stimuli of synthetic textures of diagonal lines of fixed spatial frequency. Three versions of stimuli were formed: A, a rectangle and background, which differed from each other in the orientation of the textured lines; B, isolated texture rectangle; and C, dark or light rectangular window framed by texture, C1, and C2. Thus, rectangle A was defined by the boundaries of textural cues, while B, C1, and C2 by a combination of texture and brightness signs. For control, contoured and filled rectangles were used, D and E respectively. The subjects evaluated the perceived length of the rectangles presented on the monitor screen per-forming the distance matching task. The illusion of length manifested itself in all cases. It gradually grew stronger for A, B, C1 and C2 when the length of the rectangle sincreased like in experiments with line contours D and brightness contrast E. The average values of the curves(A), (B), (C1), and (C2) were similar to each other. The data obtained confirm the assumption that the encoding of the contours of visual objects is a main prerequisite of the common sensory phenomenon, the illusion of the size of objects. The perceived shape and size are defined by local boundaries, which in turn are determined by marks of brightness or texture.