Brooke Lim¹, Anna Kosovicheva^2,3, Keisuke Fukuda^2,3; ¹McGill University, ²University of Toronto Mississauga, ³University of Toronto

Bistable perception occurs when an ambiguous stimulus triggers spontaneous alternations in perception, and these switch rates have been shown to vary across individuals. Moreover, differences in switch rates are correlated across certain classes of stimuli, indicating shared mechanisms (Cao et al., 2018). However, for bistable stimuli based on rotational motion, little is known about how individual differences in switch rates change with alterations in rotational axes. Here, participants viewed a bistable structure-from-motion sphere that rotated around either the horizontal or vertical axis on each trial. One dot, shown in a different colour, served as a perceptual landmark to examine whether perceptual switches aligned with specific spatial locations. Participants continuously indicated their perceived rotation direction via keypress while EEG was recorded. Behaviourally, participants’ perceptual switches were more frequent when the landmark approached the edges of the sphere than its center for both directions (p < 0.001). Interestingly, horizontal-axis rotation induced more frequent switches than vertical-axis rotation (t(24) = -3.47, p < .01). Additionally, those who experienced more switches in one direction also did so in the other (r = 0.57, p < .01), indicating a common mechanism of bistable perception across two rotation axes. Electrophysiologically, we successfully decoded the landmark’s physical position (p < 0.001) and the perceived direction of rotation (p < .05) above chance in both directions. Furthermore, decoding performance for landmark location was positively correlated across rotation axes, such that individuals who showed higher decoding accuracy in one direction also showed higher decoding accuracy in the other direction (r = 0.87, p < .001). Similar results were found for decoding of perceived rotation (r = 0.52, p < .01), thus providing converging support for the common mechanism of bistable perception across two rotation axes. Overall, these findings suggest that the stability of bistable stimuli is consistent across axes.