The McCollough effect: a study of some temporal characteristics

Abstract

A parametric study was made of the influence of the temporal parameters of stimulation on initial strength and rate of decay of the McCollough Effect. Using a tachistoscope to accurately control stimulus presentation timings, it was shown that the length of both the period of stimulation and intervening dark interval can affect initial strength of the aftereffect, and decay slope on log-log plot. An interpolated period of diffuse achromatic illumination may impede establishment of the aftereffect, provided the period is sufficiently long and strategically timed. The evidence indicates that strength builds up most rapidly with lengthening of the stimulation period to a second or two. For these short stimulation periods, decay is reasonably well described by a straight line on linear- log plot. Periods longer than about three or four seconds induce aftereffects having a decay better described by a straight line on log-log plot. The mechanism involved may also be sensitive to the proportion of time given to coloured pattern stimulation.
Initial strength Increases with lengthening of the duration of exposure, build-up being reasonably well described by a straight line on log-log plot. Decay slope on such a plot changes systematically for extremely long or extremely short exposures.
Temporal parameters of stimulation were also shown to affect dichoptic induction of McCollough-type aftereffects. Asynchronous onset or offset of stimulation in the two eye fields may impede, or prevent establishment of the aftereffect, timing differences of about two or three seconds being critical.
Further brief studies investigated interactions between eye channels during monocular induction of the aftereffect, and the influence of various drugs on establishment and decay of the normal McCollough Effect.