Abstract
The visual system involves various orientation and visual field anisotropies, one of which is the preference for radial over tangential orientations in the periphery. In particular, radially oriented stimuli, those that are aligned with a line intersecting the center of gaze, produce greater activity throughout the visual cortex and are associated with greater perceptual sensitivity (e.g. Sasaki et al., 2006), likely due to anatomical and physiological substrates in the early visual system (e.g. Leventhal & Schall, 1983). We recently reported a robust object-based illusion related to this preference where observers wrongly perceived peripherally placed objects to be radially aligned (Menceloglu, Nakayama, & Song, 2022). Here, we found that this preference also altered perceived motion direction. We presented ambiguous apparent motion quartets in the center of the screen while participants fixated on various locations around the quartet (9.7° visual angle away from the center of a 2.6° by 2.6° quartet). Participants (N=22) were more likely to report seeing the motion direction that was radial with respect to their fixation, accounting for their baseline direction bias measured with center fixation. We observed this bias using a vertical-horizontal quartet (typical quartet configuration) as well as an oblique quartet (45° rotated quartet), allowing us to rule out the contribution of the interhemispheric effect where interhemispheric motion is perceived less often than intrahemispheric motion in ambiguous apparent motion displays (Gengerelli, 1948). Overall, these results extend our previous radial bias findings and demonstrate a novel early-vision influence on the perceived motion direction.