EFFECT OF HEMIFIELD STIMULATION ON SIMULTANEOUS STEADY-STATE PATTERN-REVERSAL ELECTRORETINOGRAM AND VISUAL EVOKED-RESPONSE

Steady-state pattern reversal electroretinograms (PERG) and pattern re versal visual evoked responses (PVER) were recorded simultaneously in 4 normal subjects using hemifield stimulation of the upper/lower and n asal/temporal conditions with 95 and 60% stimulus contrasts. A square- wave checker-board pattern (check size 40 min of arc) was used. The te mporal frequency (reversal rate) was 6 Hz (12 reversals/s). With nasal /temporal hemifield stimulation, neither the PERG nor the PVER amplitu des differed significantly with either stimulus contrast. With the upp er/lower hemifield stimulation, PERG amplitudes were not significantly different; PVER showed a significantly larger amplitude for lower tha n for upper hemifield stimulation with both contrasts (ANOVA test: p = 0.0064, 95% contrast; p = 0.0018, 60% contrast). PVER amplitudes reco rded with lower hemifield stimulation were 2.05 and 2.63 times larger than those elicited with upper hemifield stimulation, for the 95 and 6 0% contrasts, respectively. The difference in response to the upper/lo wer hemifield stimulation, observed only in PVER, suggests that the lo wer stimulus field dominancy may be processed in a visual pathway prox imal to the retinal level.