[The specific nature of the color and brightness components of the human visual evoked potential]

In order to gain an insight into the electrophysiological cortical mechanisms of color discrimination and to compare the results with psychophysiological data summarized in the previous publications as the spherical model of color discrimination a problem was specified to identify color and brightness components of human evoked potentials. The experiments were carried out with alternating pairs of light flashes constituted of five colors (white and four main colors; red, blue, yellow, and green). Each of the light stimuli varied by seven brightness levels. Color and brightness components (N87 and P120, respectively) were reasonably reliably detected in all cases of substitution of stimuli with identical or different spectra. However, the latency and amplitude analysis of N87 and P120 components in these cases showed that N87 reflects not only color but also brightness information. It makes it possible to draw on the analogy between the N87 as one of the earliest components and N1 in primate cortical evoked potential and suggest that these components reflect the activity of cells receiving information directly from the lateral geniculate body. This process can be considered as the first stage of cortical analysis of chromatic and achromatic light characteristics. The brightness component P120, probably, represents the activity of cortical cells related to the analysis of nonchromatic stimuli characteristics, such as form, movement, orientation, etc. These characteristics are also based on luminance gradients and contrasts, however, in contrast to N87, these characteristics are not directly related with brightness of light.