Illusory Perception as a Constancy Phenomenon

Abstract

THERE are several hints in the literature of perception of a possible tie-up between constancy and the illusions, but Tausch¹ seems to have produced the first reasonably solid treatment, described clearly by Teuber², though he has not developed a fully consistent theory. Brown and Houssiadas's reference to J. J. Gibson's The Perception of the Visual World³ in this connexion is surprising, for Gibson holds a view of constancy which precludes this kind of theory. Gibson starts off (p. 163) somewhat disconcertingly: “The aim of this chapter is ultimately to show that the question of why things retain their sizes and shapes under different circumstances is a false question”. (The rest of the chapter is, however, devoted to this question.) He develops a theory of depth perception which he attributes to Koffka⁴—the size-at-a-distance theory—which is that all three spatial dimensions are equally available to the perceptual system. But in denying that depth has to be specially computed, Gibson rejects the notion of constancy scaling essential to this theory of the illusions. When Gibson uses the word ‘scale’ he is evidently not referring to a process of size adjustment normally giving constancy, for several times he explicitly denies such processes in depth perception.