Miriam Acquafredda, Claudia Lunghi, Paola Binda
Pupil size as an index of ocular dominance plasticity
Recent studies have shown that two hours of monocular deprivation alter the dynamics of binocular rivalry in favor of the deprived eye, by transiently boosting the activity of the deprived eye and suppressing the one of the non-deprived eye, measured both as VEP responses and BOLD signals. Here we investigate the effect of depriving one eye on the sensory representations of the rivalling visual stimuli with an objective measure of perceptual strength and dominance switches in binocular rivalry: pupillometry. Ten participants tracked the perceptual dynamics of binocular rivalry, while we measured pupil diameter with an Eyelink. Stimuli were white and black disks, seen through a four-mirror stereoscope, allowing each eye to see one of the disks. Four trials were administered before and after monocular deprivation, achieved by applying a translucent patch on the dominant eye for two hours. On each trial we switched the position of the stimuli, so that the deprived eye was given alternately with the black or the white stimulus. In line with previous studies, we found that subtle pupil size oscillations tracked alternations between exclusive dominance phases of the black or white disk. After monocular deprivation, the amplitude of pupil oscillations changed, but not across all conditions and not consistently across delays after patch removal. Our results show that pupillometry might index deprivation effects; however, the pattern is not immediately predictable from a chance of effective contrast and might be mediated by more complex mechanisms.