Evidence for a Fifth, Smaller Channel in Early Human Vision.

Abstract : Recent studies in psychophysics and neurophysiology suggest that the human visual system utilizes a range of different size or spatial frequency tuned mechanisms in its processing of visual information. It has been proposed that there exist four such mechanisms, operating everywhere in the visual field, with the smallest mechanism having a central excitatory width of 3 in. of arc in the central fovea. This note argues that there exists indirect evidence for the existence of a fifth, smaller channel, with a central width in the fovea of 1.5 in. (Author)