Poster Session: Characterising Visual Evoked Potential contrast response functions using achromatic and chromatic Gabor patches.

Abstract

The human visual system processes chromatic and achromatic information by adding or contrasting signals from short (S), medium (M) and long-wavelength (L) cones, through cone-additive (L+M) or cone-opponent (L-M, S-(L+M)) mechanisms. Multiple studies have shown that Visual Evoked Potentials (VEPs) to chromatic and achromatic sinusoidal gratings differ with respect to morphology. Here we characterise VEP contrast response functions to chromatic and achromatic 0.8 cycles per degree Gabors in a relatively large sample of participants (n=27). Participants view chromatic (set at individual isoluminance) and achromatic Gabors at four different contrast levels while electroencephalograms are recorded. Detection thresholds and salience matching data are also collected to establish the range of individual differences. We replicate the findings of previous normative studies: achromatic-driven pattern-onset VEPs are characterised by a robust P1 component that saturates at higher levels of contrast, while chromatic Gabors elicit a single negative deflection whose amplitude and latency depend on stimulus contrast more linearly. The data we present demonstrate the suitability of Gabors for establishing VEP-derived contrast gain functions and represent the beginnings of a comprehensive normative data set that will eventually be used for control comparisons in a large-scale study on visual function in individuals with bipolar disorder.