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Sae Kaneko, Ichiro Kuriki, Søren K Andersen; Hue selective masking: an SSVEP study. Journal of Vision 2019;19(10):69b. doi: https://doi.org/10.1167/19.10.69b.
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Are the intermediate hues (hues off the cardinal axes in the cone-opponent color space) represented as the summation of the cone-opponent mechanisms in human early visual areas? We addressed this question by smoothly scanning visual cortex responses to different hues (Experiment 1) and masking by a different hue (Experiment 2) using steady-state visual evoked potentials (SSVEPs). All colors were chosen from a hue circle on the equiluminant plane in a cone-opponent color space, whose origin was equal energy white (EEW). The stimulus was a check pattern (6 × 6 deg) on a uniform background (EEW at 30 cd/m2). In Experiment 1, half of the tiles were filled with the test hue and the other half with EEW. The tiling pattern alternated at 5 Hz, while the test hue changed smoothly at 24 s/cycle rate. Cone contrast of the test was standard (ΔL/Lbkgnd= 8 %, ΔS/Sbkgnd= 80 %), half (4, 40 %), or a quarter (2, 20 %). Participants observed the stimulus while conducting an easy detection task. In Experiment 2, half of the tiles’ hue was the test hue (flickered on/off at 5 Hz) at half contrast, while the other tiles’ was one of the four intermediate hues at the standard contrast, which flickered at 6 Hz (masker). In Experiment 1, the SSVEP amplitudes showed asymmetric patterns around the hue circle, which is consistent with the hue-selectivity study by fMRI. Data from Experiment 2 showed weakened responses to the hues around the masker hue, and the affected range spans approximately to a quadrant of the hue circle. The estimated bandwidths of hue-selective channels in previous psychophysical studies ranged 60–90 deg and our result could be a physiological support. These results suggest that the SSVEP results elucidate the characteristics of mechanisms at early cortical site selectively tuned to the intermediate hues.
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