ON THE CONTRIBUTION OF A BINOCULAR AND CHANNEL AT CONTRAST THRESHOLD

Three experiments are reported in which an attempt was made to isolate the contribution of an AND channel by measuring aftereffects followin g alternating monocular adaptation. The first two were designed to tes t Wolf and Held's proposal that the binocular AND channel does not res pond at contrast threshold. In the first experiment the relative sizes of monocular and binocular contrast threshold elevation were compared with the pattern of aftereffects obtained in a study of the suprathre shold tilt aftereffect. Identical patterns of results were obtained un der the two adaptation conditions. In the second experiment, the monoc ular and binocular contrast-reduction aftereffect reported by Blakemor e et al was measured over a wide range of reference contrasts. As in t he previous experiment, the monocular effect was greater than the bino cular effect. This occurred at all reference contrasts. These data sup port the conclusion that the AND channel contributes to visual perform ance in the same manner, irrespective of stimulus contrast. In the fin al experiment an alternative explanation for existing evidence against the existence of an AND channel was assessed.