Bay Area Vision Meeting: Position-Dependent Face Processing: Insights from the Human Brain

Bay Area Vision Meeting (more info below) Position-Dependent Face Processing: insights from the Human Brain Presented by Kalanit Grill-Spector March 7, 2011 ABSTRACT Prevailing models of face recognition in the human brain suggest a hierarchical processing stream beginning in primary visual cortex (V1) and ending in the temporal lobe in an area specialized for face recognition (fusiform face areas, FFA). Current thought is that early visual regions code low-level and local aspects of the visual stimulus in a retinotopic coordinate frame, whereas high-level regions such as the FFA code the entire face in a position invariant way. I will describe results of recent functional magnetic resonance imaging (fMRI) experiments in humans in which we examined the degree to which high-level face-selective regions are sensitive to the position of faces in the visual field. We used a novel experimental paradigm to compute fMRI voxels' population receptive fields (pRFs), that is the region in visual space that drives activation. First, using high resolution fMRI, we find that there are at least three face-selective regions in the human occipital and temporal lobes that are involved in processing faces. Second, we find that all of these regions show sensitivity to faces' position in the visual field, contrary to predictions of prevailing models. Third, these regions differ in their degree of position sensitivity and coverage of the visual field - as one ascends these stages responses become more foveal and less contra-lateral. Fourth, and most surprising, we find that responses in face-selective regions are modulated by both the type of face stimulus and its position in the visual field. In other words, we find that pRFs in face-selective regions are larger and more peripheral when mapped with larger and less crowded faces. Furthermore, the interactive effect of stimulus and position becomes more pronounced in higher face-processing stages. These results compel a revision to the existing model of the ventral processing hierarchy: position and stimulus effects interact to an increasing degree across face-processing stages in the human brain.