Hue differences and brightness differences as determinants of figural after-effects.

Abstract

Earlier published studies of the figural after‐effect using stimulus patterns in which there was no difference in brightness between the inspection figure and its background report inconsistent results. The possibility of more than one type of visual after‐effect following protracted fixation of a figure is advanced as an explanation of this inconsistency. In the three experiments described the frequency of occurrence of the figural after‐effect is investigated using inspection patterns with and without a difference in brightness between the figure and its background. Different stimulus patterns are used to allow for the occurrence of one or more possible types of after‐effect. The results from the three experiments clearly show that, with the brightness of inspection figure and ground very nearly equal, the figural after‐effect occurs with as great a frequency as in the case of a marked brightness difference. The results are discussed along with findings from earlier experiments and theoretical implications are considered. The general conclusion is that the necessary condition for the occurrence of the figural after‐effect is a visible inspection contour constituted of a difference either in brightness or in hue. A brightness difference between the inspection figure and its ground is not essential for the occurrence of the figural after‐effect.