The effect of eccentricity on the contrast response function of multifocal visual evoked potentials (mfVEPs)

MfVEPs were recorded with a 22 deg radius, 60-sector pattern reversal dartboard stimulus (VERIS) at 6 contrast levels (10, 25, 35, 50, 75, 95%). Contrast response functions (CRFs) based on response amplitudes were adequately described by a simple hyperbolic function. The effect of reducing contrast on the amplitude was most apparent in the central 1 deg radius, which had a C50 (contrast at 50% of the maximum response) in excess of 50%, compared to values for C50 in more eccentric regions that were 30% or lower. Mean latency increased 6 (± 0.7 SE) ms from the highest to the lowest contrast tested, and did not vary sgnificantly with eccentricity