Some neurophysiological correlates of visual perception.

A study was made of the structural organization of simple and complex receptive fields of the visual cortex. The bidimensional weight function of the field that determines its basic properties as a filter of spatial frequencies (spatial-frequency and orientational sensitivity) was investigated. Two types of modules-cylinders of the cortical neurons, the receptive fields of which are directed toward a single area of the visual field, and adapted to different spatial frequencies and orientations, are discussed. One type contains neurons, the receptive fields of which describe amplitude and phase of the visual signal and give Fourier descriptions of a part of the image; in the second type, the receptive fields describe only the amplitude and give the power spectrum. A comparison with psychophysical data indicates that the second type serves to describe texture. Inhibition in the receptive fields induced by frequencies lateral with respect to the optimal frequency and orientation perpendicular to optimal orientation points to the mutually inhibiting effects between neurons of the module. The significance of such an organization for visual perception is discussed.