Abstract
Recently, near infrared spectroscopy (NIRS) has been clarified awake infants' brain activity on face processing (Otsuka et al., 2006). They demonstrated that the concentration of oxyhemoglobin (oxy-Hb) and total hemoglobin (total-Hb) significantly increased in the right lateral area during presenting only upright faces, not inverted faces. This study suggests that 5-month-old infants recognize faces based on the specific mechanism in their brain.
In the present study, we investigated that (1) the measurement of infants' brain activity on perceiving frontal and profile views using NIRS and (2) the developmental changes of brain responses on both left and right temporal regions by comparing between 5- and 8-month-old infants.
Several studies indicated 6- to 8-month-olds could discriminate unfamiliar faces on different views such as three-quarter and profile views (Fagan, 1976; Nakato et al., submitted). By 8 months of age, infants can recognize faces from not only frontal but also profile views.
The participants were 13 healty infants, six 5-month-olds and seven 8-month-olds. Full color photo images of 5 vegetables, 5 unfamiliar female frontal and profile views were presented, and infants looked each photo image passively as long as they could.
Our finding was that the hemodynamic response increased in the right temporal regions at both frontal and profile views presentations. It suggests that there is an advantage of the right hemisphere in the infants' face perception, consisted with our previous NIRS study (Otsuka et al., 2006). As for the developmental change, in 5-month-old infants, the concentration of oxy- and total-Hb increased only during frontal views presentation. By contrast, in 8-month-olds the concentration of oxy- and total-Hb increased during both frontal and profile views presentations. Our hemodynamic data suggest that not 5 but 8-month-old infants would have an ability of the view-invariant representation of faces.