Figure 2. Stimulus Arrangements Reflecting IT Response-Pattern Similarity in Monkey and Human and the Interspecies Relationship.
(A) The experimental stimuli have been arranged such that their pairwise distances approximately reflect response-pattern similarity (multidimensional scaling, dissimilarity: 1 – Pearson r, criterion: metric stress). In each arrangement, images placed close together elicited similar response patterns. Images placed far apart elicited dissimilar response patterns. The arrangement is unsupervised: it does not presuppose any categorical structure. The two arrangements have been scaled to match the areas of their convex hulls and rigidly aligned for easier comparison (Procrustes alignment). The correlations between the high-dimensional response-pattern dissimilarities (1 – r) and the two-dimensional Euclidean distances in the figure are 0.67 (Pearson) and 0.69 (Spearman) for monkey IT and 0.78 (Pearson) and 0.78 (Spearman) for human IT.
(B) Fiber-flow visualization emphasizing the interspecies differences. This visualization combines all the information from (A) and links each pair of dots representing a stimulus in monkey and human IT by a “fiber.” The thickness of each fiber reflects to what extent the corresponding stimulus is inconsistently represented in monkey and human IT. The interspecies consistency ri of stimulus i is defined as the Pearson correlation between vectors of its 91 dissimilarities to the other stimuli in monkey and human IT. The thickness of the fiber for stimulus i is proportional to (1 – ri)2, thus emphasizing the most inconsistently represented stimuli. The analysis of single-stimulus interspecies consistency is pursued further in Figures S2 and S3.