A comparison of the dynamics of simple (Fourier) and complex (non-Fourier) mechanisms in texture segregation.

Models of texture segregation frequently feature two processing mechanisms: simple, linear channels (1st-order, Fourier mechanisms) and complex channels (2nd-order, non-Fourier mechanisms). Using texture patterns designed to segregate primarily as a result of activity in one set of channels or the other, we employed the method of cued response to obtain speed-accuracy tradeoff (SAT) functions measuring the time course of texture segregation processing in simple and complex channels. Here, both simple-channel and complex-channel patterns are composed of Gabor-patch texture elements, thus equating input to simple channels and the first stage of complex channels. Subjects were required to identify the orientation of a rectangular texture-region embedded in a background field of a different texture. SAT functions were obtained by requiring subjects to respond within 200 ms after an auditory cue. We found that: (1) when segregation depended primarily on activity in simple channels, performance was faster and better than when it depended primarily on complex channels; (2) in contrast to a previous study (Sutter, A., & Graham, N. (1995). Investigating simple and complex mechanisms in texture segragation using the speed-accuracy tradeoff method. Vision Research, 35, 2825-2843), simple-channel (Fourier) patterns composed of two textured regions were just as easily segregated as simple-channel patterns in which one of the regions was blank instead of textured; (3) performance with complex-channel patterns composed of diagonally oriented Gabor-patches was considerably worse than performance with complex-channel patterns composed of vertically and/or horizontally oriented Gabor-patches; (4) among simple-channel patterns containing only one region of texture (background-only or rectangle-only), there were minimal differences in performance; and (5) as in previous experiments, there were large individual differences in the segregation of complex-channel (non-Fourier) patterns. All of the above results can be explained within the framework of the simple- and complex-channels model of texture segregation.