Inter-ocular transfer of the tilt illusion shows that monocular orientation mechanisms are colour selective

A vertical grating appears tilted when surrounded by a tilted inducer grating: the tilt illusion. We investigated the inter-ocular transfer of the tilt illusion for gratings modulated along parallel or orthogonal vectors in a L − M and L + M + S cone contrast space. We found that the monocular component of the tilt illusion is entirely colour selective and the binocular component shows only weak colour selectivity. These results suggest that colour and orientation processing interact at monocular stages of visual processing, whereas binocular visual mechanisms code for form in a manner that is largely insensitive to chromatic signature.