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

mfVEPs were recorded with a 22 degrees radius, 60 sector pattern reversal dartboard stimulus (VERIS) at six 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 degrees radius, which had a C(50) (contrast at 50% of the maximum response) in excess of 50%, compared to values for C(50) 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 significantly with eccentricity.