Exploring changes in temporal contrast and perceived size

Visual illusions that affect the perceived size of an object, such as the Ebbinghaus and Delboeuf illusions, often make use of a comparison or reference disc to be able to determine the illusory effect on perceived size. In these experiments, it is also custom to include a control condition in which participants are asked to judge the size of the comparison disc presented on a neutral grey background relative to a disc of fixed size presented on the same neutral background. This control condition, however, is rarely investigated in detail. Therefore, in a series of simple experiments, we investigate how the contrast between a disc and the background on which it presented affect the discs’ perceived size. Participants are shown a disc on a background of a given intensity, after which a second disc is presented on a background of a different intensity. Participants are then asked to identify the larger of the two discs. By varying the size of one of the two discs on a trial-by-trial basis, we locate the point of subjective equality to determine if the contrast between disc and background influences the perceived size of the disc. This allows us to identify the possible contribution of figure-ground contrast to perceived size.