The neural representation of faces

UnrestrictedWhat is the nature of the representation of faces and objects that results in the striking behavioral differences in their recognition? Biederman & Kalocsai (1997) proposed that faces were represented in terms of their original spatial-filter excitation values with allowance for scale and position invariance; objects were represented as a structural description specifying arrangements of parts and relations in terms of their edge discontinuities. Behavioural and fMRI studies were conducted to examine their hypothesis. A comparison of the representation of face and nonface objects requires the same low-level processing demands for the two kinds of stimuli. To achieve this, a set of smooth, irregular 3D blobs were generated that differed only metrically (rather than nonaccidentally) and without the discontinuous edges that characterize most objects. During the fMRI experiment, subjects matched a sequence of two filtered images, each containing the content of every other combination of eight spatial frequency scales and eight orientations, of faces or of these blobs, judging whether the person or blob was the same or different. On a match trial, the images were either identical or complementary (containing the remaining spatial frequency and orientation content). The physical similarity of faces and blobs on non-match trials was equated according to a Gabor-jet model of V1 similarity (Lades et al, 1993). Relative to an identical pair of images, a complementary pair of faces, but not blobs, reduced matching accuracy and released fMRI adaptation in the right fusiform face area (FFA). These results held for both blob novices and experts who had been trained for over 8,000 trials in discriminating a different set of blobs. Moreover, the magnitude of the BOLD response to blobs in the left and right FFA was identical for experts and novices.; This outcome is contrary to claims that extensive discrimination training, in adulthood will produce face-like representation for non-face objects. Taken together the results provides strong evidence behaviorally and neurally that faces, but not nonface objects, are represented spatially (e.g., as Gabor activation values) in the FFA and that extensive adult discrimination training, cannot produce such coding for non face objects