Normative data for onset VEPs to red-green and blue-yellow chromatic contrast

Objective: To better characterize the properties of chromatic VEPs to onset -offset of red-green and blue-yellow equiluminant patterns, and establish n ormative values for a set of stimuli able to elicit robust and reliable res ponses, suitable for the clinical application. Methods: Chromatic VEPs have been recorded (Oz lead) from 28 normal subject s (age range 20-53 years) in response to monocular presentation of both red -green and blue-yellow equiluminant sinusoidal gatings. Stimuli were genera ted by a Cambridge VSG/2 card and displayed on a Barco CCID monitor (14 x 1 4 deg field size). Spatial frequency, chromaticity, contrast and onset-offs et duration were varied. Results: For both red-geen and blue-yellow equiluminant stimuli, robust res ponses have been obtained with gratings of 2 c/deg, presented in onset (300 ms) offset (700 ms) mode, at contrasts ranging from 90 to 6%. In all obser vers, the VEP waveform consisted mainly of a negative wave at stimulus onse t, with a latency rapidly increasing with decreasing contrast. For both red -green and blue-yellow stimuli, the VEP contrast threshold coincided with t he psychophysical threshold. Conclusions: The results complement previous studies aimed at characterizin g the properties of chromatic VEPs. In addition, normative data are provide d for a set of stimulus characteristics suitable for the clinical routine. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.