Some effects of changes in spiral size and viewing distance on the duration of the spiral aftereffect

Some effects of perceived size, retinal size, and retinal speed on duration of spiral aftereffect

Measures of perceived size, perceived distance, and perceived stimulus speed of rotating spirals were obtained in addition to the duration of the spiral aftereffect. Two major conditions were used: Size Constant—a 4-in. spiral was positioned to subtend visual angles of 1/2°, 1°, 2°, 4°, or 8° with 7 rates of retinal speed (10-100 minarcs/sec.) used at each angle; Angle Constant —3 sizes of spirals were positioned so that each subtended visual angles of 2°, 4°, and 8° with physical speed held constant (75 rpm) in one case and retinal speed (45 minarcs/sec.) held constant in another. SAE durations were significantly affected by low retinal speeds, by small visual angles and by perceived size per unit of retinal size.

Effects of distance and retinal velocity on duration of spiral aftereffect

Visual angle, distance, and rate of rotation were varied in 2 studies with visual acuity controlled. The studies do not support the notion that variations in visual angle or rate of rotation cause reliable differences in duration of the spiral aftereffect (SAE).

Some influences of visual angle and retinal speed on measures of the spiral aftereffect

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.