Comparison of motion aftereffect and motion fading with changes in stimulus parameters

Abstract

The motion aftereffect (MAE) and motion fading (i.e., the perception that an eccentrically viewed moving target slows to a standstill after some time) both presumably represent the adaptation of motion mechanisms. If these phenomena are mediated by the same mechanisms, then their perceived magnitudes should change similarly with changes in stimulus parameters. We studied whether MAE duration and duration to motion fading change similarly as the retinal eccentricity and rotation speed of the stimulus are changed. Fading and MAE (with 1-min adaptation) durations were determined for a 2° diameter black-and-white annular disk rotating with speeds of 4–40 rpm (1–10 Hz). Measurements of durations for three normal observers were made at retinal eccentricities of 0°–20°. Both MAE and fading durations decreased with increasing eccentricity, but both phenomena could be elicited over only a small range of eccentricities (8–12°). When the stimulus size was spatially M-scaled to compensate for the variation of cortical magnification with eccentricity, both phenomena could be elicited at most eccentricities tested (2°–20°). Duration of both the MAE and motion fading generally increased with the speed of the stimulus (8 and 20 rpm), but neither varied systematically with eccentricity. The results suggest that the two phenomena are related.