Check size and defocusing effects on equipotential maps of pattern-evoked electroretinograms.

The spatial distribution of the pattern-evoked potentials on the face was studied with a simultaneous 16-channel recording system. The potentials had the first positive component at a peak latency of approximately 55 msec, which was much earlier than the latency of the response picked up from the scalp. The maximal potential value in the maps was found at the region around the stimulated eye. This configuration of the equipotential map was not influenced by defocusing and check size of the pattern, but was altered by changing the contrast. Our results of equipotential maps constructed at around 55 msec after pattern reversal proved that the responses recorded in the facial region originated in the retina and were not a reflection of the scalp potentials.