For this, scientists from the Institut Frédéric-Joliot (CEA), Inserm and CNRS recorded the electrical brain activity of 40 babies aged 1 to 6 months. These babies were presented with different faces in the right and left fields of vision while their eyes were attracted to the center. From time to time a new face was presented, either on the right or on the left. The babies' brains, or more precisely their right hemispheres, only discriminated faces presented in their left fields of vision. Using magnetic resonance imaging, the researchers also showed that the speed of brain responses increased with the maturation of the nerve fibers connecting the visual regions of the two hemispheres. Nevertheless, this maturation is still not sufficiently effective so that the right hemisphere can take over from the "incompetent" left hemisphere in order to recognize faces presented on the right.

These results highlight important functional differences between the cerebral hemispheres that should be established from birth, in principle. They underscore the extreme cerebral organization of the human baby in the first months of life, which is far removed from the notion of a piece of clay shaped by the environment.