Expert face processing requires visual input to the right hemisphere during infancy.

Adult expertise in face processing is mediated largely by neural networks in the right hemisphere. Here we evaluate the contribution of early visual input in establishing this neural substrate. We compared visually normal individuals to patients for whom visual input had been restricted mainly to one hemisphere during infancy. We show that early deprivation of visual input to the right hemisphere severely impairs the development of expert face processing, whereas deprivation restricted mainly to the left hemisphere does not. Our results indicate that the neural circuitry responsible for adults' face expertise is not pre-specified, but requires early visual experience. However, the two hemispheres are not equipotent: only the right hemisphere is capable of using the early input to develop expertise at face processing.