Shape constancy: Functional relationships and theoretical formulations.

In the 1st section empirical findings concerning shape constancy are reviewed under 10 headings: the occurrence of compromise, conditions of observation, degree of orientation, observation attitude, familiarity and representativeness, differences between forms, individual differences, background effects, effects of movement, exposure time and intensity. The 2nd section deals with several theoretical accounts of shape constancy. The shape-slant invariance hypothesis is evaluated in the light of the experimental evidence and is judged to be equivocal. A line of investigation is proposed which might reconcile the experimental data with the requirements of this hypothesis. The final section of the paper considers the methodological precautions which need to be observed in experimentation on apparent shape and apparent slant. When a form is projected by light on the retina, the differing orientations of the form with regard to the retina result in a set of different projective shapes. Under most conditions phenomenal shape is less affected by the orientation of the stimulus object with respect to the observer (0) than would be expected on the basis of the projective transformations which accompany variations in orientation. The term "shape constancy" has been introduced to designate this fact. Shape constancy is defined usually as the relative constancy of the perceived shape of an object despite variations in its orientation. This definition reflects the prevalent interest in the stability of the perceptual world. However, it is also possible to locate shape constancy within a wider range of events all characterized by a relative independence of perceived shape from retinal, projective shape. With this in mind, the phenomena relevant to