The time course of binocular rivalry during the phases of the menstrual cycle.

Binocular rivalry occurs when markedly different inputs to the two eyes initiate alternations in perceptual dominance between the two eyes' views. A link between individual differences in perceptual dynamics of rivalry and concentrations of GABA, a prominent inhibitory neurotransmitter in the brain, has highlighted binocular rivalry as a potential tool to investigate inhibitory processes in the brain. The present experiment investigated whether previously reported fluctuations of GABA concentrations in a healthy menstrual cycle (Epperson et al., 2002) also are associated with measurable changes in rivalry dynamics within individuals. We obtained longitudinal measures of alternation rate, dominance, and mixture durations in 300 rivalry tracking blocks measured over 5 weeks from healthy female participants who monitored the start of the follicular and luteal phases of their cycle. Although we demonstrate robust and stable individual differences in rivalry dynamics, across analytic approaches and dependent measures, we found no significant change or even trends across menstrual phases in the temporal dynamics of dominance percepts. We found only sparse between-phase differences in skew and kurtosis on mixture percepts when data were pooled across sessions and blocks. These results suggest a complex dynamic between hormonal steroids, binocular rivalry, and GABAeric signaling in the brain and thus implicate the need to consider a systemic perspective when linking GABA with perceptual alternations in binocular rivalry.