Lip-reading and eye-gaze discrimination are functionally lateralized across the left and right posterior superior temporal sulci.

The posterior superior temporal sulcus (pSTS) processes information from the eyes and the mouth that support social perception. To investigate the laterality of how these mechanisms function, we performed three experiments on lip and eye-gaze discrimination. In Experiment 1, participants (n = 18) performed lip-position and eye-gaze discrimination tasks in static facial expressions while transcranial magnetic stimulation (TMS) was delivered over the left and right pSTS. Results showed a double dissociation in which disruption of the left pSTS impaired the lip-position task, while disruption of the right pSTS impaired the eye-gaze matching task. In Experiment 2, participants (n = 16) performed a lip-reading task using dynamic video clips of a speaker while TMS was delivered over the left and right pSTS. Task performance was impaired when TMS was delivered over the left pSTS only. In Experiment 3, participants (n = 256) underwent resting-state functional magnetic resonance imaging. Results demonstrated that the left pSTS exhibited greater connectivity to language processing brain areas in the left hemisphere. In contrast, the right pSTS exhibited greater connectivity to visual areas specialized for face processing and spatial attention processing. Our study suggests that lip and eye-gaze discrimination are preferentially lateralized across the bilateral pSTS.