r Seghier et al. r Figure 1. A: Main effect of semantic matching on words relative to per- level (random-effect analysis on the LM maps over 82 sub- ceptual matching on unfamiliar greek letters (random-effect jects, at P < 0.001 uncorrected). C: laterality indices (LI) of analysis over 82 subjects, at P < 0.001 uncorrected). Signiﬁ- our 82 subjects. For display purposes, individual LI values are cant effects are shown in red-to-yellow color coding and pro- sorted from weak to strong left-lateralization. [Color ﬁgure jected on an individual T1-weighted image in neurological can be viewed in the online issue, which is available at convention. B: Consistent effect of laterality at the voxel wileyonlinelibrary.com.] perceptual letter matching.’’ About 9,100 voxels within the left hemisphere satisﬁed these criteria (see Supporting In- formation Fig. S2). The clustering of these voxels was based on between subject variance such that voxels were clustered together when variance across subjects was strongly correlated. We used the following parameters (c.f., [Seghier and Price, 2009]): 50 for the number of clus- ters, 1.5 for the degree of fuzziness, and the hyperbolic correlation as a distance metric [Golay et al., 1998]. All voxels that belong to a given cluster are then characterized by the centroid of that cluster. In other words, this data reduction procedure summarized the laterality of all vox- els into 50 clusters (i.e., 50 centroids with 82 datapoints in the across subject dimension). Once the voxel based laterality map had been reduced to 50 compact clusters, we correlated laterality at the cent- roids of each cluster with that in every other cluster (from 1 to 50 clusters). This resulted in a 50-by-50 correlation (similarity) matrix. The aim was to identify any strong negative correlations (at P < 0.001 uncorrected). The results were visualized using multidimensional scaling (MDS, for a similar procedure see [Kherif et al., 2003; Welchew et al., 2002]). RESULTS Voxel Based Second Level Analyses The analysis of the original (unﬂipped) contrast images from 82 subjects revealed a left dominant pattern of semantic word matching activation, see Figure 1A. In the r 1606 r