Interocular grouping of negative afterimages after binocular rivalry

Abstract

Afterimage (AI) formation is based on both retinal mechanisms and perception (Gilroy & Blake, 2005; Shimojo et al., 2001). Here we propose an amended view that AI can be formed independent of perception. Stimuli in each eye were a centrally presented 2 by 2 array of grating squares (1 cycle/deg). Each element subtended 3°. In one eye, gratings in two diagonal quadrants were vertical, while those in the other quadrants were horizontal. The orientations of the corresponding elements in the other eye were orthogonal. Complete interocular grouping might produce coherent percepts of single large vertical or horizontal gratings. While for incomplete grouping, one could perceive two types of partially integrated patterns. Otherwise, the monocular stimuli were perceived. Both during and after each induction period (55s), 10 subjects reported their percepts according to the 4 types. Surprisingly, although all types were perceived with close probability during induction (22.5% ~ 27.3%), subjects reported seeing the AIs of coherent patterns much more frequently (57.3%). Alternating presentation of the two inducers binocularly failed to reproduce this effect (N = 9). To ensure the observed effect was specific to AIs, we measured it with varied inducing contrasts [.04 .08 .16 .35 1]. For all the contrast conditions, the predominance for the coherent percepts was significantly higher (N = 20, p < .01) during the AI period (70.6%) than during the induction (< 38.6%). Because of micro eyemovements, AIs might be rendered blurry like low-pass filtered stimuli. So we filtered the inducers with a low-pass filter (< 0.5 cpd retained), but still observed similar effects (N = 16, coherent percepts: 74.5% (AIs) vs. < 41.9% (inducers)). These findings suggest that AI formation after binocular rivalry adaptation is strongly dominated by the mechanisms that favor coherent percepts, while during induction such effects could be largely corrected by monocular feed-forward signals. Meeting abstract presented at VSS 2015