The processing of faces across non-rigid facial transformation develops at 7 month of age: a fNIRS-adaptation study.

Background: Using near-infrared spectroscopy (NIRS), our previous neural adaptation studies found that infants' bilateral temporal regions process facial identity (FiHN 5:153, 2011). In addition, we revealed that size-invariant processing of facial identity develops by 5 months of age (NR 23:984-988, 2012), while view-invariant processing develops around 7 months of age (FiHN 5:153, 2011). The aim in the current study was to examine whether infants' brains process facial identity across the non-rigid transformation of facial features by using the neural adaptation paradigm. We used NIRS to compare hemodynamic changes in the bilateral temporal areas of 5- to 6-month-olds and 7- to 8-month-olds during presentations of an identical face and of different faces.

Results: We found that (1) the oxyhemoglobin concentration around the T5 and T6 positions increased significantly during the presentation of different faces only in 7- to 8-month-olds and (2) 7- to 8-month-olds, but not 5- to 6-month-olds, showed attenuation in these channels to the presentation of the same face rather than to the presentation of different faces, regardless of non-rigid changes in facial features.

Conclusions: Our results suggest that the processing of facial identity with non-rigid facial transformation develops around 7 months after birth.