Abstract
Motion can bias the perceived location of a stationary stimulus (Whitney & Cavanagh, 2000). However, it has not been established whether this occurs at a high-level of representation, or at early, retinotopic stages of visual processing. As coding of orientation emerges early in the visual processing stream, we tested whether motion could influence the spatial location at which orientation adaptation is seen. Specifically, we examined whether the tilt aftereffect (TAE) depends on the perceived or the retinal location of the adapting stimulus, or both. We employed the flash-drag effect to produce a shift in the perceived position of the adaptor away from its retinal location. On each trial, subjects viewed a patterned disc that oscillated clockwise and counterclockwise. Subjects adapted to a small disc containing a tilted linear grating that was flashed briefly at the moment of the rotation reversals. The flash-drag effect biased the perceived location of the grating in the direction of the disc's motion immediately following the flash, allowing dissociation between the retinal and perceived location of the adaptor. Following an interstimulus interval of 100 ms, brief test gratings were presented at one of three locations—the retinal or perceived location of the adaptor, or an equidistant control location (antiperceived). Measurements of the TAE at each location—the spatial tuning of the TAE—demonstrated that the TAE was usually strongest at the retinal location, and tended to be larger at the perceived compared to the antiperceived location. This indicates a skew in the spatial locus of the TAE in the direction of background motion. Together, our findings suggest that motion can bias the location of low-level adaptation.