A number of behavioral studies suggest that infant-directed speech (ID) plays a more important role in facilitating both: a) speech perception, and b) adult-infant social interactions than does adult-directed speech (AD), and hence that ID contributes to subsequent social and language development. However neural substrates that may underlie these ID functions have not been examined. The present study examined cerebral hemodynamic responses to ID in 48 infants (3-13 months of age) using near-infrared spectroscopy (NIRS). Japanese sentences uttered by the infants  own mothers and by unfamiliar mothers were used to record activations in temporal and frontal area separately. Increased activations were observed predominantly in infants left and right temporal areas when they listened to ID rather than to AD when both involved voices of their own and unfamiliar mothers. In contrast, significantly greater activations were observed in the frontal area when infants listened to ID produced by their own mothers, not when ID arose from unfamiliar mothers. Together, these findings suggest that: a) ID, but notadult directed speech, increases cerebral activity in the temporal area of infants whether produced by a familiar or unfamiliar voice; and b) ID specific to the voice of an infant's own mother facilitates activity in the frontal areas.

特集 : 小嶋祥三君退職記念
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