Abstract
keywords: Color vision, cortical color mechanisms, SSVEPs, intermodulation components, tuning functions, cardinal color axes, intermediate color axes Color information is thought to be received by the primary visual cortex via two dominant retinogeniculate10 pathways, one signals color variation between teal and red, and the other signals color variation between11 violet and lime. This representation is thought to be transformed in the cortex so that there are a number12 of different cell populations representing a greater variety of hues. However, the properties of cortical13 color mechanisms are not well understood. In four experiments, we characterized the tuning functions of14 cortical color mechanisms by measuring the intermodulation of steady-state visually evoked potentials15 (SSVEPs). Stimuli were isoluminant chromatic checkerboards where odd and even checks flickered at16 different frequencies. As hue dissimilarity between the odd and even checks increased, the amplitude of17 an intermodulation component (I1) at the sum of the two stimulus frequencies decreased, revealing18 cortical color tuning functions. In Experiment 1 we found similar broad tuning functions for ‘cardinal’ and19 intermediate color axes, implying that the cortex has intermediately tuned color mechanisms. In20 Experiment 2 we found similar broad tuning functions for ‘checkerboards’ with no perceptible edges21 because the checks were formed from single pixels (~0.096°), implying that the underlying neural22 populations do not rely on spatial chromatic edges. In Experiment 3 we manipulated check size and found23 that color tuning functions were consistent across check sizes used. In Experiment 4 we measured full 360°24 tuning functions for a ‘cardinal’ cortical color mechanism and found evidence for opponent color25 responses. The observed cortical color tuning functions were consistent with those measured using26 psychophysics and electrophysiology, implying that tracking intermodulation using SSVEPs provides a27 useful method for measuring them.28
Authors
Watts, D.J., Rozman, A., Somers, L.P., Gunel, B., Racey, C., Barnes, Bosten, K. &., & J.M.
https://doi.org/10.1162/IMAG.a.130