Face identity may be represented in anterior IT rather than in FFA
Characterizing brain regions by representational similarity structure. For each region, a similarity-graph icon shows the similarities between the activity patterns elicited by four stimulus images. Images placed close together in the icon elicited similar response patterns. Images placed far apart elicited dissimilar response patterns. The color of each connection line indicates whether the response-pattern difference was significant for the group (red: p<0.01; light gray: pâ‰¥0.05, not significant). A connection line, like a rubberband, becomes thinner when stretched beyond the length that would exactly reflect the dissimilarity it represents. Connections also become thicker when compressed. Line thickness, thus, indicates the inevitable distortion of the 2D representation of the higher-dimensional similarity structure. The thickness of the connection lines is chosen such that the area of each connection (length times thickness) precisely reflects the dissimilarity measure. This novel visualization of fMRI response-pattern information combines (a) a multidimensional-scaling arrangement of activity-pattern similarity (as introduced to fMRI by Edelman et al., 1998), (b) a novel rubberband-graph depiction of inevitable distortions, and (c) the results of statistical tests of a pattern-information analysis (for details on the test, see Kriegeskorte et al., 2007). The icons show fixed-effects group analyses for regions of interest individually defined in 11 subjects. Early visual cortex was anatomically defined; all other regions were functionally defined using a data set independent of that used to compute the similarity-graph icons and statistical tests.
Face-exemplar information in FFA and aIT as a function of ROI size. When we define FFA by the category contrast (Fig. S1) and vary the threshold to select between 10 and 4000 contiguous voxels, significant face-exemplar information is not found at any threshold (blue, dashed: left FFA; blue, solid: right FFA). When we define the "FFA vicinity" as the 4000 cortical voxels in a sphere centered on FFA in each subject and hemisphere (Fig. S1) and select the n voxels containing most face-exemplar information on independent data, significant face-exemplar information is not found for any threshold (magenta, dashed: left FFA vicinity; magenta, solid: right FFA vicinity). When we define aIT in each subject and hemisphere as the 4000 anterior-most voxels in temporal cortex and, again, select the n voxels containing most face-exemplar information on independent data, no significant face-exemplar information is found for the left hemisphere (red, dashed). However, robust face-exemplar information is found in right aIT (red solid). The figure shows group results for regions of interest defined in each individual subject. Independent data were used for (1) defining the regions and voxel weights and (2) testing the multivariate effects and estimating face-exemplar information.