Separation of contour and area dependent components in the first and second order kernels of the multifocal pattern appearance evoked potential.

The non-linearities of the diffuse flash visual evoked potential (VEP) have been shown to generate separable waves corresponding to Magnocellular and Parvocellular contributions. The authors wished to investigate whether, under conditions of isoluminance, the chromatic pattern appearance VEP shows waveforms that are related to both the processing of contours (the pattern) and the processing of the diffuse stimulation (from the area lying between the contours). The VERIS multifocal system was used to record monocular VEP. Standard 2-ring, 3-ring, 5-ring and 7-ring VERIS pattern stimuli were employed with a cardboard circular aperture used to blank the stimulus monitor to a 9-cm diameter field. The results for four subjects were recorded. The first order kernel responses showed a significant increase in amplitude with total contour length. In comparison, the amplitudes of the first and second slices of the second order kernel did not increase with contour length. It appears that the contour-dependent component has negligible non-linear components. It is proposed that the constant, non-zero responses of the higher order kernel components reflects contributions from the diffuse chromatic VEP.