The effect of check size on VEPs in healthy humans: a parabolic relationship between check size and N145 wave.

The effect of check size on pattern reversal VEPs was examined in healthy adult volunteers. The subjects were exposed to full-field binocular stimulation. Five checkerboard patterns with check sizes 13', 25', 50', 75' and 100' were used as the visual stimuli. The patterns reversed at a rate of 1 reversal/sec. Well-defined pattern reversal VEPs were obtained for all check sizes in all subjects. As the check size increased a transition from a triphasic to an almost monophasic wave form was observed. N75 and P100 amplitudes, together with N75 latency, revealed linear relationships with check size; the N145 amplitude displayed a parabolic relationship with check size. No significant relationships were found for P100 and N145 latencies. It is concluded that the N75 wave originated mainly from the activity of the foveola, whereas the more eccentric regions contribute more to the formation of P100, and the interaction of both regions elicited the N145 wave.