Valerie Nunez^1,2, James Gordon^2,3, Robert Shapley²; ¹Renaissance School of Medicine, Stony Brook University, ²Center for Neural Science, NYU, ³Hunter College, CUNY

This is about testing the hypothesis that color-responsive neurons in Human primary visual cortex, V1, can be partitioned into two groups: single-opponent (SO) and double-opponent (DO) as were found in monkey V1. The experimental test was measurements of Chromatic Visual Evoked Potential (cVEP) responses vs spatial frequency in 16 human observers. Observers viewed equiluminant “red-green” checkerboard patterns modulated from 0 to 0.16 Michelson contrast in the L-M/M-L direction of DKL color space. Temporal color modulation was a rectangular wave, 0.5s on, 1.5s off. The checkerboard was equiluminant with a gray 18deg by 10deg Background (luminance 30 cd/m2); during stimulus-on, checkerboard replaced a circular region of Background roughly 2.5deg in diameter. Check size was varied to vary the dominant spatial frequency (SF) of the checkerboard from 0.6 up to 9.0 c/d. Observers also viewed color-modulation of spatially uniform fields. We identified the SO cVEP as a rapid transient (peak time ~80 ms) that was present only for checkerboards at low SF or for uniform fields; the SO waveform was not observable for SF>1.7 c/d. Separately, there was a large negative peak (peak time ~ 120-150 ms) that we and many others have assigned to the DO population. The cVEPs of DO cells were SF-tuned with a peak response ~ 3 c/d. The color responses of Human SO and DO cells have distinct temporal and spatial signatures suggesting they are indeed independent.

Acknowledgements: This project was supported by the US National Science Foundation (grant number 1753846)