In two experiments subjects were required to determine whether a random, angular form, presented at any of a number of picture-plane orientations was a "standard" or "reflected" version. Average time required to make this determination increased linearly with the angular departure of the form from a previously learned orientation. (Author/BJG)

Based on the more general principle that all thinking (including reasoning) is basically perceptual in nature, the author proposes that visual perception is not a passive recording of stimulus material but an active concern of the mind. He delineates the task of visually distinguishing changes in size, shape, and position and points out the…