Similarities and dissimilarities between pattern VEPs and motion VEPs

The contrast response functions (CRF) of pattern-appearance and motion-onse t VEPs for periodic stimuli (gratings) were compared. The CRF for pattern-a ppearance is accelerative for the P100 component and compressive for the N2 00 component. Contrary to these results, the CRF for motion-onset shows an almost negligible slope for both components within the contrast range teste d (0.5-64%). To better isolate the neural contributions to these different VEP components, we studied the effects of prior adaptation to stationary an d moving gratings. Adaptation to stationary gratings has no effect on both VEP components for motion-onset and the P100 component for pattern-appearan ce, but did reduce the amplitude of the N200 for pattern-appearance. Adapta tion to slow (1 deg/s) and fast (4 deg/s) gratings left the P100 amplitudes unaltered, while it significantly reduced the N200 amplitudes for both pat tern-appearance and motion-onset. These results suggest that the N200 compo nent of the motion-onset VEP is generated by motion-dependent neurons, wher eas the same component for pattern-appearance arises from contrast-dependen t neurons. The observed differences between P100 and N200 components appear to reflect the activity of both transient and sustained neural mechanisms.