Duration of Spiral Aftereffect as a Function of Retinal Size, Retinal Place, and Hemiretinal Transfer

Abstract

This experiment has shown that, although both rods and cones mediate the spiral aftereffect, cone areas give a larger response. Increasing size of the retinal image results in longer durations of SAE but rods are more affected by this increase than are cones. There is a general weakening in aftereffect resulting from “transfer” from one hemiretina to another with cone areas showing greater loss than rod areas. Size of retinal image has been shown to be a potent variable and, in fact, under some small size conditions, normal Ss fail to observe any effect whatsoever. In view of these findings, it is apparent that size of retinal image is a variable which must be carefully controlled if comparable results are to be obtained. Review of the clinical literature, however, reveals that distance from S to spiral and objective spiral size often vary from experiment to experiment. This variation could well account for some of the differences in results of clinical studies. It is proposed that a standard spiral size and testing distance be introduced for clinical use.