Structure of a complex receptive field in the cat visual cortex

Abstract

The most common type of complex receptive field, whose response to the passage of sinusoidal gratings across it consisted of modulated and unmodulated components, was analyzed. The use of a mask to cover half the field, according to the filter theory, led to widening of the transmission band of the field as a spatial frequency filter, due to the appearance or enhancement of the response at lateral low and high frequencies. Modulated components of responses from the left and right halves of the field were out of phase. Analysis of this fact, and also of responses of the field to thin light and dark bars enabled the field structure to be described. It consists of linear and nonlinear subsystems, converging on the output neuron of the complex field. The former is composed of several pairs of on- and off-subfields of the lateral geniculate body. The on- and off-subfields in the pair overlap spatially and converge on the output neuron of the linear subsystem with opposite signs. The nonlinear subsystem is composed of either on- or off-subfields. Other types of complex fields may include different combinations of subsystems. The results indicate that complex fields are spatiotemporal grating filters.