Abstract

Much about the perceived segregation of regions containing different textures can be explained by simple channels (linear, first-order, Fourier processes), but nonlinear processes are also needed. In addition to complex channels, an intensive nonlinearity—one dramatically compressing responses at contrasts well below 25%—is necessary to explain results of varying the sign and amount of contrast in multiple-element textures (Graham, Beck, and Sutter, 1992, Vision Research). This intensive nonlinearity might arise either from an early local nonlinearity preceding the channels or from normalization (perhaps due to intracortical inhibition) among the channels themselves. To decide between these two candidate intensive nonlinearities, we tried several approaches, including variation of the patterns' overall spatial characteristics and careful comparison of effects at different contrast levels in the two element types of a single pattern. Although deciding between the candidates has been more difficult than we had hoped, the weight of the evidence suggests that normalization at the level of the channels, rather than a local nonlinearity preceding the channels, causes the compressive effects in perceived texture segregation.

© 1992 Optical Society of America