Contingency and the McCollough effect

According to a Pavlovian conditioning analysis of the orientation-contingent color aftereffect (the McCollough effect), orientation stimuli become associated with simultaneously presented chromatic stimuli. This account suggests that decreasing the contingency between the putative conditional stimulus (grid orientation) and the unconditional stimulus (color) should decrease the strength of the aftereffect. In the present experiment, the effect of presentations of achromatic grids and/or homogeneous chromatic stimuli between presentations of chromatic grids was evaluated. Although interpolated achromatic grid presentations did decrease the magnitude of the McCollough effect, interpolated chromatic stimuli had no effect on the magnitude of the phenomenon. The results are discussed in terms of current research concerning the selective associability of certain categories of conditional and unconditional stimuli, and differences in the development of associations between simultaneously (compared with successively) presented conditional and unconditional stimuli.