Fig. 2: fMRI results showing sensitivity to illusory faces in face-selective cortex.

a Schematic visualization of the four functional regions of interest; each region was defined individually in each hemisphere of each subject from their functional localizer. b Results of cross-decoding (train and test the classifier on brain activity associated with different exemplars so generalization across stimuli is required) the three stimulus categories from four regions of interest. The mean decoding accuracy is shown, averaged over N = 16 participants. Asterisks indicate conditions with statistically significant decoding, evaluated using one-sample t-tests (one-tailed) and FDR adjusted *p values < 0.05, and ***p values < 0.001 to correct for multiple comparisons. The distinction between human faces and objects with (FFA: p = 0.00004, OFA: p = 0.0005, LO: p = 0.0002, PPA: p = 0.0008) or without an illusory face (FFA: p = 0.00001, OFA: p = 0.0002, LO: p = 0.0003, PPA: p = 0.0002) can be decoded from activation patterns in all regions. Illusory faces can be discriminated from similar matched objects from activity in FFA (p = 0.015) and OFA (p = 0.020) only, but not in LO (p = 0.11) and PPA (p = 0.40). Error bars are SEM. Source data are provided as a Source data file. c Representational dissimilarly matrices (96 × 96) for all stimuli for the four regions of interest. The dissimilarity is calculated by taking 1-correlation (Spearman) between the BOLD activation patterns for each pair of stimuli. The colorbar range is scaled to the max and min of the dissimilarity values for each ROI for visualization. White lines indicate stimulus category boundaries. Insets show 3 × 3 matrices for each ROI averaged by category, excluding the diagonal. Source data are provided as a Source data file. d Visualization of the dissimilarity matrices in (c) using multidimensional scaling. The first two dimensions following MDS are plotted, each of the points representing the 96 stimuli is colored according to its category membership. Proximity of the points represents more similar brain activation patterns for the stimuli. Note that in the FFA and OFA, the illusory faces are more separated from the matched objects and closer to the human faces compared to LO and PPA.