PMC

Plot of function A_D(·) for different values of D.

Spatial maps of the face selective regions found by the significance test (light blue) and the mixture model (red). Slices from the each map are presented in alternating rows for comparison. The approximate locations of the two face-selective regions FFA and OFA are shown with yellow and purple circles, respectively.

Group system selectivity profiles in the 16-Dimensional data for (A) 8, and (B) 12 clusters. The colors (blue, black) represent the two distinct components of the profiles corresponding to the same category, and the weight q for each system is also indicated along with the consistency score (cs) and its significance value found in the permutation test.

Sets of 10 discovered group system selectivity profiles for (A) 8-Dimensional, and (B) 32-Dimensional data. Different colors (blue, black, green, red) represent different components of the profiles corresponding to the same category. We added zero to each vector to represent Fixation. The weight q for each selectivity profile is also reported along with the consistency score (cs) and the significance value.

Null hypothesis distributions for the consistency score values, computed from 10,000 random permutations of the data. Histograms A, B and C show the results for 8, 16, and 32-Dimensional data with 10 clusters, respectively. Histograms D, E, and F correspond to 8, 10, and 12 clusters in 16-Dimensional data (B and E are identical). We normalized the counts by the product of bin size and the overall number of samples so that they could be compared with the estimated Beta distribution, indicated by the dashed red line.

(A) A set of 10 discovered group system selectivity profiles for the 16-Dimensional group data. The colors (black, blue) represent the two distinct components of the profiles corresponding to the same category. We added zero to each vector to represent Fixation. The weight q for each selectivity profile is also reported along with the consistency scores (cs) and the significance values found in the permutation test, sig = −log₁₀ p. (B) A set of individual system selectivity profiles in one of the 6 subjects ordered based on matching to the group profiles in (A).

An example of voxel selectivity profiles in the context of a study of visual category selectivity. The block design experiment included several categories of visual stimuli such as faces, bodies, scenes, and objects, defined as different experimental conditions. (A) Vectors of estimated regression coefficients β̂ = [β_Faces, β_Bodies, β_Scenes]^t for the voxels detected as selective to bodies, faces, and scenes in one subject. As is common in the field, the conventional method detects these voxels by performing significance tests comparing voxel's response to the category of interest and its response to objects. (B) The corresponding selectivity profiles y formed for the same group of voxels.

The results of mixture model density estimation with 5 components for the set of selectivity profiles in . The resulting system selectivity profiles (cluster centers) are denoted by the red dots; circles around them indicate the size of the corresponding clusters. The box shows an alternative presentation of the selectivity profiles where the values of their components are shown along with zero for fixation. Since this format allows presentation of the selectivity profiles in general cases with D > 3, we adopt this way of illustration throughout the paper. The first selectivity profile, whose cluster includes most of the voxels in the overlapping region, does not show a differential response to our three categories of interest. Selectivity profiles 2, 3, and 4 correspond to the three original types of activation preferring faces, bodies, and scenes, respectively. Selectivity profile 5 shows exclusive selectivity for bodies along with a slightly negative response to other categories.