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

Ensemble models of the movement aftereffect and the influence of eccentricity

Moving random-pixel arrays (RPAs) were used to study the movement aftereffect (MAE) for translational texture motion and to quantify the contribution of RPA-sensitive motion sensors to the MAE as a function of eccentricity. Size-scaled patterns were used to make a fair comparison across eccentricities. At the upper end of the velocity range it was found, for all eccentricities, that motion sensors tuned to velocities exceeding about 10-20 deg s-1 do not contribute to the translational MAE, even though they do contribute to motion perception. As a consequence the subpopulation of local motion sensors that contributes to the MAE shrinks with eccentricity, because there are fewer low-velocity-tuned and more high-velocity-tuned motion sensors for increasing eccentricity. Thus there is a quantitative, but not a qualitative, difference between the MAEs generated at different eccentricities.

Duration of the motion aftereffect as a function of retinal locus and visual field

The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.

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.

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

Duration of the spiral aftereffect (SAE) was investigated with spirals of 2, 4, 8, 12, 14, and 16 inches in diameter. The distance of the spirals from the observers was varied to produce visual angles between 1°12′ and 18°56′ of arc. Data indicate that peak SAE durations occur approximately between 2° and 4° of visual angle.