Control of visuotemporal attention by inferior parietal and superior temporal cortex

The human cortical visual system is organized into two major pathways: a dorsal stream projecting to the superior parietal lobe (SPL), considered to be critical for visuospatial perception or on-line control of visually guided movements, and a ventral stream leading to the inferotemporal cortex, mediating object perception [1-3]. Between these structures lies a large region, consisting of the inferior parietal lobe (IPL) and superior temporal gyrus (STG), the function of which is controversial. Lesions here can lead to spatial neglect [4,5], a condition associated with abnormal visuospatial perception [6,7] as well as impaired visually guided movements [8, 9], suggesting that the IPL + STG may have largely a "dorsal" role. Here, we use a nonspatial task [10] to examine the deployment of visuotemporal attention in focal lesion patients, with or without spatial neglect. We show that, regardless of the presence of neglect, damage to the IPL + STG leads to a more prolonged deployment of visuotemporal attention compared to lesions of the SPL. Our findings suggest that the human IPL + STG makes an important contribution to nonspatial perception, and this is consistent with a role that is neither strictly "dorsal" nor "ventral" [11]. We propose instead that the IPL + STG has a top-down control role, contributing to the functions of both dorsal and ventral visual systems.