Some Influences of Visual Angle and Retinal Speed on Measures of the Spiral Aftereffect

Abstract

Duration and intensity of the SAE were judged under five conditions: Angle Constant (A)—retinal speed and visual angle were held constant across several spiral-size, viewing-distance combinations; Size-Constant—a single spiral size was used at several distances, with retinal speed either varied (S1) or held constant (S2); Distance Constant—several spiral sizes were used at a constant distance with retinal speed either varied (D1) or held constant (D2). Duration and intensity measures were affected similarly, with perceptual rather than physical variables seeming to account for the results. Assuming that perfect size constancy occurred during the experiment, SAE durations were longer, in general, for larger values of perceived size per unit of retinal size. Retinal speed variation had no apparent influence, except possibly at low values.