Adult observers quickly identify the specific actions performed by the invisible actor from the points of lights attached to the actor's head and major joints. Even infants are already sensitive to biological motion and prefer it depicted by the dynamic point-light display (Arterberry & Bornstein 2001). To detect biological motion such as whole body movements and facial movements, neuroimaging studies demonstrated involvement of occipitotemporal cortex including superior temporal sulcus (STS) (Lloyed-Fox et al., 2009). In the present study, we applied the point-light display technique and examined infants' brain activity while watching facial biological motion in the point-light display by using near-infrared spectroscopy (NIRS). Dynamic facial point-light displays (FPD) were made from video recordings. As in Doi et al. (2008), about 80 luminous markers were scattered pseudo-randomly over the surface of the actors' face. Three actors performed the surprised expression in the dark room and were videotaped. In the experiment, we measured hemodynamic responses by using NIRS. We hypothesized that infants would show differential neural activity for upright and inverted FPD. The responses were compared to the baseline activation during the presentation of individual still images those were frames extracted from the dynamic FPD. We found that the concentration of oxy-Hb and total-Hb increased in right lateral area during the presentation of the upright FPD compared to the baseline period. The results suggested that (1) the brain activity while watching the facial movement in point-light display would develop by 6-8-months of age, (2) processing of the facial biological motion related to the right lateral area.
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