Bruno Richard¹ (), Robert Hess², Sing Ip Lee³, Daniela Marinova³, Daniel Baker³; ¹Rutgers University - Newark, ²McGill University, ³University of York

The visual system encodes binocular signals via summing and differencing channels, yet the relative weighting of these pathways remains unclear. Here, we use Steady-State Visually Evoked Potentials (SSVEPs) to investigate the neural responses associated with summing and differencing mechanisms. In Experiment 1, we measured responses to binocular noise stimuli in 15 observers. Across the eyes, stimuli could oscillate (at 3Hz) from no correlation to perfect interocular correlation, from no correlation to perfect interocular anticorrelation (i.e., opposite interocular contrast), or no interocular correlation (i.e., the control condition). Responses to correlated stimuli showed a peak at the fundamental frequency (3Hz); however, we found no evidence of measurable responses to anticorrelation. In Experiment 2, we increased the sample size to 48 observers and measured SSVEPs in response to interocular correlation and anticorrelation while manipulating the degree of interocular correlation. The correlation between the left and right eye images could be ±0, 0.12, 0.24, 0.48, or 0.96. We found SSVEP responses at the fundamental frequency in both interocular correlation and anticorrelation conditions. Interocular correlation generated SSVEPs with a correlation of 0.48 or 0.96, while anticorrelation SSVEPs were only measurable at a correlation of -0.96. Signal-to-noise ratios were 1.15 times larger for the correlation condition than the anticorrelation condition. To determine the influence of individual differences on SSVEPs to interocular correlation, we collected psychophysical measures of binocular function and correlated them with neural responses. Two measures of binocularity were used: stereoacuity and binocular balance, which refers to the ratio of dominance duration in each eye during rivalry. We found only small associations between SSVEP magnitudes and psychophysical measures of binocularity (stereoacuity and binocular balance). We conclude that while neural responses to both correlation and anticorrelation can be recorded via SSVEPs, the latter requires high signal coherence and a large sample size.