Characteristics of complex channels (second-order processes) in perceived texture segregation

Abstract

Aspects of perceived texture segregation suggest the existence of complex channels. A complex channel consists of two linear-filtering stages separated by a rectification-type nonlinearity, a structure like that hypothesized for a complex cortical cell. We tested this proposed structure by having human observers rate the degree of segregation between two textures, each composed of the same two types of elements but in differing arrangements (checkerboard vs. striped arrangements). The two element types were Gabor patches of the same spatial frequency and orientation but differing in size (number of cycles at half-maximal contrast). A tradeoff between contrast and size was found, approximating that predicted for Gabor-patch elements by complex channels (analogous to that predicted for square elements by simple first-order channels—Sutter, Beck, and Graham, 1989, Perception and Psychophysics). Elaborations of the model may be necessary, however. Further, we investigated complex-channel characteristics including (i) bandwidths of first- and second-stage filters and (ii) mapping rules specifying first-stage-second-stage combinations of preferred spatial frequencies and orientations.