Effect of hemifield stimulation on simultaneous steady-state pattern reversal electroretinogram and visual evoked...

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