Atypical Binocular Rivalry Dynamics of Simple and Complex Stimuli in Autism

Background: Binocular rivalry occurs when conflicting images are presented to the same retinal location of each eye. The two percepts compete for perceptual dominance, and conscious perception alternates between the two. The dynamics of binocular rivalry are proposed to index the balance of excitatory and inhibitory connections in the brain, and have therefore been proposed as markers of an imbalance in excitatory/inhibitory transmission that may characterize autistic neurobiology. Two studies have compared rivalry dynamics in individuals with and without Autism Spectrum Conditions (ASC), each using stimuli of different levels of visual complexity. While both found results in the expected direction, only one found significant differences in rivalry dynamics between the two groups.

Objectives: First, we hoped to replicate our previous finding of a slower rate of rivalry with longer mixed percepts in ASC in a new, expanded sample of participants. Second, we tested whether this finding was selective for stimuli of a particular level of visual complexity.

Methods: 53 participants (26 with ASC) completed twelve 40s trials of binocular rivalry (6 with object stimuli, 6 with grating stimuli) and 24 control trials. Participants continuously reported either dominant or mixed percepts throughout the trial. We analysed the rate of perceptual transitions and average percept durations as well as ratios of percept durations.

Results: We tested rivalry dynamics with Stimulus Type as between-subject factor and ASC Diagnosis as within-subject factor in repeated measures ANOVA. ASC subjects perceived a lower rate of switches (F(1, 51) = 4.3, p < 0.043) with  longer mixed percepts (F(1, 51) = 14.7, p < 0.001). The differences in average mixed percepts and proportion of mixed percepts were confirmed with non-parametric comparisons of means to be significant in both stimulus conditions, while the difference in switch rate was significant only in the grating condition.

Conclusions: We replicate our previous findings of a slower rate of binocular rivalry with increased mixed percepts in ASC, and show that these effects are present at low levels of stimulus complexity. These results are predicted by an increased ratio of excitatory/inhibitory synaptic transmission in autism, and suggest that this imbalance may manifest as early as V1.