Effect of stimulus intensity and contrast on the pattern ERG

Stripe patterns of varying spatial frequency were presented in the onset-offset mode. At a high contrast the amplitude of the onset response showed a spatial selectivity which occurred with a high intensity at a higher spatial frequency than with a low intensity. The offset response showed only a monotonic decrease in amplitude at both intensities. Contrast sensitivity functions were derived at different levels of contrast. The spatial selectivity of the onset response occurred at a contrast spatial frequency and was more pronounced with low contrasts. The amplitude of the offset response was spatially selective only at low contrasts; with increasing contrast a gradual shift to a non-selective behavior was noted.