Chapter 8 : Dynamics of perceptual bi - stability : plaids and binocular rivalry compared

This chapter presents a set of findings about the dynamics of bi-stable alternations in the perception of plaids. A plaid is a pattern comprised of two superimposed gratings. When the plaid is set in motion, it becomes an ambiguous stimulus: it can be seen as one pattern moving in a single direction (“coherency”), or as two gratings, each moving in different directions with one sliding over the other (“transparency”). The two possibilities are illustrated in Figure 8.1A. In prolonged viewing, the perception of moving plaids switches back and forth between the coherent and the transparent interpretations – a classic example of perceptual bi-stability. Hans Wallach, who was the first to use superimposed gratings to study motion perception, discussed their bi-stability at some length (Wallach, 1935, Wallach, 1976, Wuerger, Shapley & Rubin, 1996). However, in the modern literature this aspect of plaid perception has been virtually forgotten. Since Adelson and Movshon (1982) re-introduced plaids as a tool for studying motion processing, researchers have been using brief presentation 2AFC methods, overlooking the dynamical aspect (but see von Grunau & Dubé, 1993). We therefore decided to give the bi-stable alternations in plaid perception a closer look.