Evidence of basal temporo-occipital cortex involvement in stereoscopic vision in humans: A study with subdural electrode recordings

Stereoscopic vision is based on small differences in both retinal images known as retinal disparities. We investigated the cortical responses to retinal disparities in a patient suffering from occipital epilepsy by recording evoked potentials to random dot stereograms (RDS) from subdural electrodes placed in the parieto-occipito-temporal junction, medial surface of the occipital lobe (pericalcarine cortex) and basal surface of the occipital and temporal lobes (fusiform gyrus). Clear responses to disparity present in RDS were found in the fusiform cortex. We observed that the fusiform responses discriminate the onset from the offset of the stimulus, correlation from uncorrelation, and they show a longer latency than responses found in the pericalcarine cortex. Our findings indicate that the fusiform area is involved in the processing of the stereoscopic information and shows responses that suggest a high level of stereoscopic processing.