Thérèse Collins¹, Steven Shevell; ¹Université Paris Cité & CNRS, Paris, France, ²University of Chicago, Departments of Psychology and Ophthalmology & Visual Science, Chicago, IL, USA

Stimulus history can shape perceptual experience by attracting or repulsing subsequent stimuli. The well-known phenomenon of serial dependence (SD) quantifies the degree to which an immediately previous stimulus alters the perception of a current one. We used monocular versus binocular stimulus presentation to investigate the neural level at which SD occurs. Participants indicated whether the direction of motion of a random dot kinematogram (RDK) presented for 500 ms was CW or CCW relative to a reference direction. In Experiment 1, RDKs were binocular and coherence varied (25%, 75%, 100%). Reported percepts were repulsed away from the previous direction (e.g., a previous counterclockwise stimulus increased clockwise reports for the current stimulus). In Experiment 2, RDKs were presented to observers either monocularly or binocularly at 25% or 100% coherence. With a current monocular stimulus, serial dependence was greater when the previous stimulus was binocular rather than monocular. This suggests a mechanism mediating SD is driven by binocular combination. Experiment 3 had three presentation conditions: 100% coherence presented to both eyes, 50% coherence presented to both eyes, or 0% coherence presented to the left eye + 100% coherence to the right eye. If SD depends on the binocularly fused coherence then the 50% binocular and 0/100% conditions should result in the same magnitude of SD. Repulsion was strongest from the 100% binocular RDK and weakest from the 50% binocular RDK, as expected; the mixed 0/100% RDK caused intermediate repulsion. Results from these three experiments show that repulsive serial dependence increases with the coherence of the previous stimulus, and is driven by a response at a binocular level of neural integration though not simply by the coherence of the fused binocular percept.

Acknowledgements: International Institute for Research in Paris, University of Chicago