How do infants perceive scrambled face?: A near-infrared spectroscopic study.

Using near-infrared spectroscopy (NIRS), we recorded changes of oxy-Hb, deoxy-Hb, and total-Hb in 7- to 8-month-old infants' and adults' brains in response to canonical face and scrambled face stimuli. Using a newly developed probe for NIRS recording, which was light and soft enough to be tolerated by infants, we were able to acquire data from the very young even in the awake state. Total-Hb in response to a canonical face stimulus was greater than for scrambled face stimuli only in the right hemisphere in infants. This indicates the presence of right hemisphere dominance of brain activity in response to face images in 7- to 8-month-old infants. In adults, oxy-Hb and total-Hb were significantly increased from baseline only for the canonical face in the right hemisphere. There were greater numbers of channels showing significantly increased activity for the canonical face in the right than in the left hemisphere. These data indicate that the right hemisphere is more dominant for canonical face perception in both infants and adults. However, overall, the increase of total-Hb and oxy-Hb in adults was modest compared to infants. Although the reason for the difference between infants and adults is unclear, in addition to developmental changes influencing face perception, some methodological problems may be present. Thus, because we recorded NIRS signals in infants and adults using the same method, anatomical and physiological problems might affect the results to some degree. Although comparing the results between infants and adults is not simple, the present study is the first to indicate how 7- to 8-month-old infants perceive scrambled face stimuli and to compare such results with those of adults in order to understand developmental changes in face perception.