Spatial-frequency- and orientation-selectivity of simple and complex channels in region segregation.

Models incorporating spatial-frequency- and orientation-selective channels explain many texture-segregation results, particularly when known nonlinearities are included. One such nonlinearity is complex channels. A complex channel consists of two stages of linear filtering separated by a rectification-type nonlinearity. Here we investigate the spatial-frequency- and orientation-selectivity of simple (linear) channels and of the complex channels' first stage. Observers rated the degree of segregation between two "textures" both composed of elements which were Gabor patches. When the textures differed in type of element (e.g. one composed of vertical and the other of horizontal Gabor patches), the segregation results yield bandwidth estimates for simple channels of approx. 0.5-1.0 octave on the spatial-frequency dimension and 5-20 deg of rotation on the orientation dimension. When the textures differ in the arrangement of elements (e.g. striped vs checkerboard arrangements, both of horizontal and vertical patches), the segregation results yield bandwidth estimates for the first stage of complex channels. These estimates, while differing substantially from one observer to another, were always substantially wider than those for simple channels (by at least a factor of two) but narrower than bandwidths of LGN cells (particularly on the orientation dimension where LGN cells show little selectivity at all).