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.
Laron
Michal
M
College of Optometry, University of Houston, 505 J Davis Armistead Bldg, Houston, TX 77204-2020, USA.
Cheng
Han
H
Zhang
Bin
B
Frishman
Laura J
LJ