Abstract

The visual system readily discriminates certain black-and-white textures whose spatial frequency spectra (or autocorrelations) are identical. This implies that preattentive texture discrimination is based on local features, and not just global spatial frequency content. The psychophysi­cal distinguishability of such isodipole textures is paralleled by an evoked-potential component elicited by texture interchange. Psychophysical and evoked-potential measures of discrimination among a library of isodipole texture pairs force rejection of computational models based on symmetry, information content, or a single nonlinear stage. Models with two nonlinear stages, which consist of local nonlinear subunits whose outputs combine in a spatially specific and cooperative fashion, are consistent with experimental observations. In order for such models to maintain sensitivity and specificity over a wide range of contrasts, modulation of one or both nonlinear stages by local contrast is required. This model structure is consistent with features of connectivity within striate cortex. A spatiotemporal analog of this model may account for joint extraction of Fourier and non-Fourier motion.

© 1992 Optical Society of America