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Amy L. Thomas, Geoffrey K. Aguirre; Distributed representation of facial identity studied with fMRI. Journal of Vision 2006;6(6):667. doi: 10.1167/6.6.667.
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© ARVO (1962-2015); The Authors (2016-present)
Visual stimuli may be represented by ensembles of neuronal activity. We tested if the perceptual similarity of faces is reflected in the similarity of neural patterns evoked by those faces.
During pilot studies, the pair-wise, perceptual similarity of 27 photo-realistic, synthetic faces was determined. During fMRI scanning, subjects viewed repeated, counterbalanced presentations of the faces while they performed a perceptual judgment orthogonal to face similarity (a separate manipulation of apparent age). The pattern of fMRI activity across voxels was obtained for each face, and used to create a matrix of pair-wise similarity measures of neural responses between the face stimuli. This matrix of neural similarity was then correlated with a separately obtained matrix of perceptual similarity, as well as a physical (pixel-based) measure of stimulus similarity. These analyses were conducted for voxels within ventral extra-striate cortex (VES) and within earlier visual areas (V1/V2).
Within VES, the average correlation across subjects between perceptual and neural measures of face similarity was 0.22 (diff from zero, p=1.7e-5). The physical similarity matrix produced significantly (p=0.004) lower correlations (r=0.17). Within V1/V2, the correlation of the neural similarity matrix with the perceptual (r=0.08) and physical (r=0.10) measures were significantly weaker (p=0.005). Physical similarity fit the neural responses within V1/V2 better than perceptual similarity, although not significantly so (p=0.15).
A measure of facial representation can therefore be derived from large scale patterns within VES. We are currently determining the degree to which categorically defined cortical regions within VES (i.e., FFA, PPA, LOC) contribute to this representation.
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