Fig. 4. Asymmetric similarity changes in the left inferior frontal gyrus (left IFG).
a Asymmetry in learning reflects the extent to which the representation of the B face after learning became more similar to that of the A face before learning than the representation of the A face that became similar to that of the B face (Bpre). In accordance, the multivoxel activity pattern of the B face post learning (Bpost) was correlated with the pattern of the A face pre-learning (Apre), and the pattern of the A face post learning (Apost) was correlated with the pattern of the B- face pre-learning (Bpre). Then, the latter similarity value was subtracted from the former as shown above, to reflect the extent to which the B face became more similar to the A face than the A face became to the B face. We interpreted asymmetry as assimilation of the B face into the representation of the A face. b Asymmetry was observed in the left IFG in the prior knowledge (PK) pair type for paired faces only, but not in the no-prior-knowledge (n-PK) pair type. N = 19. Data in the bar graphs are presented as mean values, error bars reflect +/− SEM. **P = 0.01, results of a one-sample two-tailed t test against zero. ***P = .002, results of a paired-sample two-tailed t test between PK-paired and PK-shuffled pairs, as depicted by the black lines. c Dots reflect individual participants’ PK asymmetry difference (PK-paired vs. PK-shuffled). To protect copyrights, all faces in the figures are of novel faces, and we obtained permission to use these photos. Participants in the study saw famous and novel faces, as detailed in Methods.