Losses in peripheral colour sensitivity predicted from "hit and miss" post-receptoral cone connections.

On the basis of the early primate neurophysiological recordings, it was thought that the different cone types of the primate retina project selectively into the centre and surround of the receptive fields of cone opponent neurons, and more recently this view has been reasserted on the basis of physiological results. An alternative idea is that these projections are in fact unselective for cone type, and, therefore, cone opponency arises from chance variations in the proportions of different cone types in centre and surround. The issue is presently controversial with anatomical or physiological support for both hypotheses. Our results show that there is a selective loss of red-green colour sensitivity across the human visual field. Furthermore, this selective loss occurs under low temporal frequency conditions (0.5 Hz) which were selected to favour the mediation of both colour and luminance detection by a common P cell pathway and to exclude an M cell contribution to detection threshold. We show that "hit and miss" post-receptoral cone projections will produce a decline in cone opponency that is sufficient to account for this selective loss, thus providing psychophysical evidence consistent with this hypothesis.