Surface orientation discrimination activates caudal and anterior intraparietal sulcus in humans: An event-related fMRI study

Perception of surface orientation is an essential step for the reconstructi on of the three-dimensional (3D) structure of an object. Human lesion and f unctional neuroimaging studies have demonstrated the importance of the pari etal lobe in this task. In primate single-unit studies, neurons in the caud al part of the intraparietal sulcus (CIP) were found to be active during th e extraction of surface orientation through monocular (two-dimensional) cue s such as texture gradients and linear perspective as well as binocular (3D ) cues such as disparity gradient and orientation disparity. We used event- related fMRI to study the functional neuroanatomy of surface orientation di scrimination using stimuli with monocular depth cues in six volunteers. Bot h posterior (CIP) and anterior (AIP) areas within the intraparietal sulcus showed a stronger activation during surface orientation as compared with a control (color discrimination) task using identical stimuli. Furthermore, t he signal changes in CIP showed a greater performance effect than those in AIP, suggesting that CIP is tightly linked to the discrimination task.