Directional effects of size change on the comparison of visual shapes.

Recent studies have investigated the effect of an irrelevant size change on reaction time in tasks involving comparison of same or different shapes. In most cases, however, studies have examined simultaneous presentation or else successive presentation where the second stimulus was always larger than the first. In the present study, subjects made same-different shape judgments on successively presented closed geometric forms, where the second form was smaller than, larger than, or the same size as the first. Comparison reaction times were observed to increase with increasing size difference regardless of the direction of size change (i.e., when the second figure was either larger or smaller than the first). In addition, the effects of size change were identical for both "same" and "different" responses. These findings were seen to support an analog normalization process in which subjects mentally equate the figures for size before comparing their shapes. The relation of these results to previous data is discussed.