Location of human face-selective cortex with respect to retinotopic areas

Early widespread cortical distribution of coherent fusiform face selective activity

Intracranial EEG was analyzed from 16 pharmaco-resistant epilepsy patients. Subjects participated in memory tasks for faces and/or words. Face-selective coherence increases were found between the fusiform gyrus and temporal, parietal, and frontal cortices at 160-230 ms poststimulus onset. Word stimuli elicited weak or negligible response at the same latency. Phase lag increased monotonically with distance from the fusiform region. The slope was consistent with conduction velocities of myelinated cortico-cortical pathways. These results suggest that the contribution of the fusiform gyrus to face processing at around 200 ms poststimulus onset is rapidly projected to widespread cortical regions.

The representation of illusory and real contours in human cortical visual areas revealed by functional magnetic resonance imaging

Illusory contours (perceived edges that exist in the absence of local stimulus borders) demonstrate that perception is an active process, creating features not present in the light patterns striking the retina. Illusory contours are thought to be processed using mechanisms that partially overlap with those of "real" contours, but questions about the neural substrate of these percepts remain. Here, we employed functional magnetic resonance imaging to obtain physiological signals from human visual cortex while subjects viewed different types of contours, both real and illusory. We sampled these signals independently from nine visual areas, each defined by retinotopic or other independent criteria. Using both within- and across-subject analysis, we found evidence for overlapping sites of processing; most areas responded to most types of contours. However, there were distinctive differences in the strength of activity across areas and contour types. Two types of illusory contours differed in the strength of activation of the retinotopic areas, but both types activated crudely retinotopic visual areas, including V3A, V4v, V7, and V8, bilaterally. The extent of activation was largely invariant across a range of stimulus sizes that produce illusory contours perceptually, but it was related to the spatial frequency of displaced-grating stimuli. Finally, there was a striking similarity in the pattern of results for the illusory contour-defined shape and a similar shape defined by stereoscopic depth. These and other results suggest a role in surface perception for this lateral occipital region that includes V3A, V4v, V7, and V8.