Investigating the Neural Representation of Face Categories

Faces are highly relevant for social communication of humans and other primates. There is evidence suggesting similar categorical representations of faces and objects in human and monkey's temporal lobes. However, differences are likely to be found at a finer granularity scale, given the environmental adaptability of neurons in this area and the difference in relevance of tested stimuli across species. Understanding differences and similarities in the neural representations of humans and monkeys is currently an important issue in behavioral neuroscience. In this doctoral thesis the author and collaborators compared the neural representation of species-dependent face categories in human and monkey observers. As the relevance of several kinds of faces varies across species, differences in the representation of own-species' versus other-species' faces are expected. To be able to compare representations across species, experimenters here used the same human/monkey face stimulus continuum, similar tasks and the same multivariate analysis approach. Consistent with the psychophysical results, fMRI experiments showed a categorical representation biased towards prototypical human faces in the left human STS. In addition, activation in the ventral temporal cortex was most sensitive to deviations from the human prototype. Symmetrically and consistently with monkey behavioral data, extracellular signals recorded from monkey temporal lobe also showed a categorical representation of the continuum, but biased towards the monkey end of the continuum. In sum, the behavioral and neural data show a symmetric own-species bias in the categorical representation of these face categories in both species. These results might reflect specialized neural mechanisms for the processing of privileged face categories.