A Neural Signature of Similarity Assessment between a Face and One’s Own Face

Facial similarity to one’s own face indirectly affects a person’s social behavior. In this study, we aimed to develop, using multivariate pattern analysis, a brain signature for assessing facial similarity to one’s own face (SFSS). We hypothesized that it should have at least two aspects: one related to the assessment of similarity of faces, and the other specifically to the assessment of similarity to one’s own face. To distinguish between these aspects, we included two tasks that used the same set of morphed images, but in one case the task was to assess similarity to one’s own face and in the other to another person’s face. The SFSS showed excellent correlation with behavioral data and a large effect size in predicting the instantaneous similarity score for each participant. Mediation analysis showed that it acts as a mediator between the degree of similarity objectively present in an image and the subjective similarity assessment. Principal component analysis allowed to separate brain regions associated with the assessment of face similarity in general and with judging the similarity to one’s own face. It appeared that the early visual cortex was particularly involved in the former, while the fusiform gyrus and orbitofrontal cortex were involved in distinguishing targets. The results show the fruitfulness of considering brain signatures as representations of complex psychological processes, which can be analyzed by decomposing them into components to represent different aspects of relevant psychological states.