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Rory Sayres, Kevin Weiner, Serge Dumoulin, Brian Wandell, Kalanit Grill-Spector; Population receptive field measurements in human ventral category-selective cortex. Journal of Vision 2009;9(8):734. doi: 10.1167/9.8.734.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Category-selective regions in extrastriate cortex are conventionally defined by comparing responses to images from different categories (e.g., faces vs. houses). What is the representation of the visual field in these regions? Are separate category-selective regions part of a single map or embedded within a set of distinct visual field maps?
Methods: We scanned seven subjects on separate experiments to localize category-selective regions, and measure visual field maps (GE 3T scanner). For retinotopic experiments, subjects viewed moving bar stimuli containing different stimuli, including slowly drifting checkerboards and frontal face images. The bars extended out to ∼14° eccentricity from the fovea, with a width of ∼2.6°. We employed a recently-developed method for estimating population receptive fields (pRFs) using fMRI (Dumoulin and Wandell, Neuroimage, 2008), which estimates pRF center and size for each cortical location.
Results: Face-containing bars produced substantially larger responses than checkerboards along the fusiform gyrus, improving our ability to measure visual field maps in these regions. Eccentricity maps revealed two foveal representations, which may correspond to visual field map clusters previously identified as VO and VT (Wandell et al., Neuro-opth. Jpn., 2006). These foveas are within or adjacent to fusiform face-selective regions, and separated by smoothly-varying extra-foveal maps which are less face-selective.
For several subjects, pRF sizes systematically increased with eccentricity in face-selective regions. The distribution of pRF sizes were substantially larger than in earlier visual cortex, but comparable to recent measurements made in lateral occipital cortex. Current work addresses possible effects of low-level visual features (e.g. spatial frequency) and stimulus visibility in driving the observed face-selective retinotopic responses.
Conclusion: We find two spatially separate face-selective regions along the fusiform gyrus, with comparable visual field coverage, separated by a representation of intermediate eccentricities. This indicates these two regions are likely to fall within different visual field maps.
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