Decoding of EEG signals reveals non-uniformities in the neural geometry of colour*

The idea of colour opponency maintains that colour vision arises through the comparison of two chromatic mech-anisms, red versus green and yellow versus blue. The four unique hues, red, green, blue, and yellow, are assumed to appear at the null points of these the two chromatic systems. Here we hypothesise that, if unique hues represent a tractable cortical state, they should elicit more robust activity compared to other, non-unique hues. We use a spatiotemporal decoding approach to report that electroencephalographic (EEG) responses carry robust informa-tion about the tested isoluminant unique hues within a 100-350 ms window from stimulus onset. Decoding is possible in both passive and active viewing tasks, but is compromised when concurrent high luminance contrast is added to the colour signals. For large hue-differences, the efficiency of hue decoding can be predicted by mutual distance in a nominally uniform perceptual colour space. However, for small perceptual neighbourhoods around unique hues, the encoding space shows pivotal non-uniformities which suggest that anisotropies in neurometric hue-spaces may reflect perceptual unique hues.

Automated summary

The concept of colour opponency suggests that colour vision is based on the comparison of two chromatic mechanisms: red versus green and yellow versus blue. Unique hues, including red, green, blue, and yellow, are assumed to correspond to the null points of these chromatic systems. This study demonstrates that electroencephalographic responses carry robust information about tested unique hues within a specific timeframe. The efficiency of hue decoding is influenced by luminance contrast and perceptual neighbourhoods.