Size-invariant representation of face in infant brain: an fNIRS-adaptation study.

We studied whether 5-month-old to 8-month-old infants process faces in a size-invariant manner by applying the fNIRS-adaptation paradigm used in our previous study. We used near-infrared spectroscopy to measure hemodynamic responses in the temporal regions of infants' brains during the repeated presentation of an identical face and different faces while changing the size of the faces. As a result, we found that (a) the hemodynamic responses in the channels around the T5 and T6 positions increased significantly during the presentation of different faces and (b) the hemodynamic responses in these channels showed attenuation to the presentation of the same face compared with the presentation of different faces even when the size of the faces altered. Our findings indicated that infants could show adaptation to the same face despite size alterations and that this processing occurred in the bilateral temporal areas.