Residual motion discrimination using colour information without primary visual cortex.

Previous studies have reported that some patients with damage to striate cortex retain the ability to detect monochromatic light and discriminate direction of achromatic movement in their blind visual fields. We investigated the residual chromatic visual capacity of a well-studied patient (GY) who has a unilateral lesion to striate cortex (V1). The data demonstrated that GY was able to detect and discriminate isoluminant colour targets presented in his blind hemifield. The velocity and contrast of chromatic moving stimuli affected GY's levels of conscious experience of movements he was able to discriminate. As the velocity or contrast was increased, his discrimination performance improved in line with rising visual awareness and judgement confidence. At isoluminance, GY continued to discriminate motion direction with above chance accuracy. These results indicate chromatic signals can also be used to process motion information in the absence of primary visual cortex.