[Motion-onset visually evoked potential with nasal and temporal half- and full-field stimulation]

The known proportional increase in the amplitude of the pattern reversal visually evoked potential (VEP) with increasing stimulus area does not occur for the motion-onset VEP. When the stimulus area of the total field (6 degrees x 6 degrees) is compared to that of the half-field (6 degrees x 3 degrees), the N200 amplitude of the motion-onset VEP is not changed proportionally but remains almost constant. Reducing the pattern contrast beyond the saturation value for the motion-VEP yields essentially the same results. Contrary to the pattern reversal VEP, the amplitudes of the motion-onset VEP are found to be more pronounced for the nasal than for the temporal hemiretina. Our results support the notion of a genuine difference between the pattern- and the motion-analyzing visual system.