Figure 2.

Hippocampal distance code for concept space revealed by fMRI adaptation. A, Schematic of two-dimensional object positions and distances between objects in concept space (left) and three-dimensional object positions and distances between objects in feature space (right). B, Average of contrast of parameter estimates (cope) of the 2D versus 3D distance adaptation regressors in all hippocampal voxels. Hippocampal adaptation decreases with increasing two-dimensional conceptual distance between successively presented objects significantly more than with three-dimensional feature-based distance between objects. C, Control for complexity difference between two- and three-dimensional representation: two-dimensional distances from conceptual space (xy) were compared with two-dimensional distances derived from a combination of the conceptually relevant x-axis (left) and y-axis (right) with the irrelevant z-axis. If the better fit of 2D(xy) distances versus 3D distances (B) reflects a preference of the hippocampus for 2D codes, 2D(xy) should not fit better than 2D(xz) or 2D(yz). Bars reflect the mean. Central marks of the boxes indicate the median, the bottom and top edges of the boxes indicate the 25th and 75th percentiles, whiskers extend to extreme data points not considered outliers; outliers are plotted as red crosses. Asterisk (*) indicates significance at p < 0.05.