Assessing variations in eye dominance across the visual field

Eye dominance (ED) in humans is not a unitary phenomenon: it depends on the method used (e.g. the Porta test, or sensory ED assessed by binocular rivalry), and it can vary over the visual field: both in the extent to which one eye (locally) dominates over the other, and in which eye dominates at a certain location. We used a variant of a new method, tracking Continuous Flash Suppression (tCFS; Alais et al, bioRxiv 2023), to rapidly assess ED across the visual field. TCFS is based on breaking Continuous Flash Suppression (bCFS). With the latter, a target gradually increasing in intensity is presented to one eye, while a dynamic mask is presented to the other. The observer responds when the target becomes visible. In our bCFS-experiments, a target-mask pair was presented at -10, 0 and 10 deg from fixation. In our variant of tCFS, a target-mask pair moved horizontally across the visual field (from -10 to 10 deg at 1 deg s-1), and the observer continuously increased and decreased the intensity of the target, respectively to make it visible and invisible. In Experiment 1A (bCFS, n=18) & 1B (tCFS, n=18), the mask contrast was 50%; in Experiment 2A (bCFS, n=18) & 2B (tCFS, n=18), it was 25%. ED varied over the visual field: observers had parts in the visual field at which one of the eyes was dominant, and parts where this was not the case. We even encountered observers with right ED for one location, and left ED for another. We also replicated the recently reported nasal visual field advantage for both methods (the nasal visual field of one eye dominates over the temporal hemifield of the other). Finally, we validated the new method by showing that ED assessed by tCFS correlated significantly with that assessed by bCFS.