Human Perception of Affine Equivalent Polygons

Abstract

One of the central problems in the study of visual form is the phenomenon of shape constancy, the fact that humans tend to see figures as having the same shape or form if they differ only in position, orientation, size, and mirror reflection. Research about the perception of form undergoing orientational change has been dominated by the concept of mental rotation. There is some behavioral evidence suggesting that when processing geometrically transformed shapes, human observers are mentally transforming the internal representations of the shapes in order to make certain decisions about them (Shepard and Cooper, 1982). For example, Shepard and Metzler (1971) found that the time taken by subjects to determine the identity of two objects was proportional to the angle between them. That is, the subjects behaved as though they mentally rotated one of the objects at a constant rate until both were at the same orientation. Likewise, Bundesen and Larsen (1975) reported that the reaction time needed to notice the identity of figures of the same shape and in the same orientation but of different size, increased linearily as a function of the size ratio of the figures. Again, they suggested that a process of mental size transformation could explain this finding.