Human parietal cortex structure determines individual differences in perceptual rivalry

Abstract

When visual input has conflicting interpretations, conscious perception may alternate spontaneously between them. There is a large amount of unexplained variability between individuals in the rate of perceptual switches. We investigated whether variability in perceptual rivalry is reflected in individual differences in brain structure. To do so, we collected perceptual switch rates for a structure-from-motion (SFM) stimulus from a group of 52 participants and examined whether variability in brain structure across participants could account for the individual differences in switch rate. We found that the gray matter volume of posterior superior parietal lobe (SPL) in both hemispheres correlated positively with inter-individual differences in switch rate, but an opposite relationship was found only in the anterior part of right SPL. Furthermore, causal influences of these areas on perceptual switch rate were confirmed using transcranial magnetic stimulation (TMS). Transient disruption of both left and right posterior SPL by TMS slowed switch rates, whereas disruption of right anterior SPL made the rate faster. These findings suggest that right anterior SPL is involved in maintenance of the current percept, while posterior SPL prompts switches to alternative percepts. The contrasting causal roles of the anterior and posterior parts of right SPL in perceptual rivalry suggest a functional fractionation of these regions in human right parietal cortex.