Effects of spatially structured stimulus fields on pattern reversal visual evoked potentials.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 healthy individuals. A photic stimulator for pattern production on a TV monitor, an electroencephalograph for EEG signal amplification and a computer for averaging the potentials and displaying the traces were used in the experiments. The peak latencies and both trough-to-peak and baseline-to-peak amplitudes of the main PRVEP components were found to be closely related to both the check size of checkerboard pattern and the bar width of barred pattern. The latencies decreased exponentially and amplitudes varied non-monotonically with check size or bar width. Most of the amplitudes of these components were greatest when checkerboard patterns with check sizes subtending visual angles of 60--70 min of arc, or barred patterns with bar widths subtending angles of 7--15 min of arc, were presented.