Complex visual textures as a tool for studying the VEP

A method of separating components of the visual evoked potential by using complex visual textures is described. Interchange of visual textures with identical power specta and third-order autocorrelations elicits a response which may be analyzed into symmetric and asymmetric components. It is shown that the asymmetric component depends on complex attributes of form. Mechanisms that generate this component must possess nonlinear interactions among multiple areas of the visual pattern. These interactions are likely to be more complex than rectification following spatial summation. It is concluded that the asymmetric component reflects intracortical, rather than precortical, processsing.