The rich and immediate perception of a familiar face, including its identity, expression and even intent, is one of the most impressive shared faculties of human and non-human primate brains. Many visually responsive neurons in the inferotemporal cortex of macaque monkeys respond selectively to faces1,2,3,4, sometimes to only one or a few individuals5,6,7, while showing little sensitivity to scale and other details of the retinal image8,9. Here we show that face-responsive neurons in the macaque monkey anterior inferotemporal cortex are tuned to a fundamental dimension of face perception. Using a norm-based caricaturization framework previously developed for human psychophysics10,11,12, we varied the identity information present in photo-realistic human faces13, and found that neurons of the anterior inferotemporal cortex were most often tuned around the average, identity-ambiguous face. These observations are consistent with face-selective responses in this area being shaped by a figural comparison, reflecting structural differences between an incoming face and an internal reference or norm. As such, these findings link the tuning of neurons in the inferotemporal cortex to psychological models of face identity perception.
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We are grateful to G. Rhodes, N. Kriegeskorte and N. K. Logothetis for critical comments on the manuscript, and to A. Maier, M. Wilke and K.-M. Mueller for discussions. We especially thank C. Wallraven, B. Knappmeyer and H. H. Bülthoff for conducting experiments aimed at selecting the perceptually most dissimilar faces serving as the stimuli for C99. This work was executed at the Max Planck Institute for Biological Cybernetics, and was supported by a Max Planck Society grant to N. K. Logothetis, as well as grants from the Volkswagen Foundation, DFG and HFSP (to M.A.G.). Author Contributions D.A.L and I.V.B originated the experiment and performed the neurophysiological recordings. All authors performed data analysis and discussed the results. D.A.L. and M.A.G. wrote the paper.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Leopold, D., Bondar, I. & Giese, M. Norm-based face encoding by single neurons in the monkey inferotemporal cortex. Nature 442, 572–575 (2006). https://doi.org/10.1038/nature04951