Cortical processing of color: Chromatic visual evoked potentials

Evoked potentials measured from human visual cortex reveal that, in humans as in other primates, color is represented in the cortex mostly by neurons that are spatially-tuned. This means that color perception is most affected by spatial patterns of color and by the color difference across the boundaries of colored regions. The evidence from cortical evoked responses also supports the concept that the cortex does away with the strict segregation of color and luminance signals, and of red-green vs blue-yellow signals, that is present in its thalamic input. Rather, all combinations of cardinal direction signals are used by the population of spatially-tuned, color-responsive cortical neurons in the visual cortex. The neural populations that combine color signals are sometimes called Higher Order Color Mechanisms. These fundamental findings about color processing in the cortex challenge the classical theory of opponent colors. Also, they show that color is computed in combination with space and form, not separately.