Human infants orient to biological motion rather than audiovisual synchrony.

Both orienting to audiovisual synchrony and to biological motion are adaptive responses. The ability to integrate correlated information from multiple senses reduces processing load and underlies the perception of a multimodal and unified world. Perceiving biological motion facilitates filial attachment and detection of predators/prey. In the literature, these mechanisms are discussed in isolation. In this eye-tracking study, we tested their relative strengths in young human infants. We showed five-month-old infants point-light animation pairs of human motion, accompanied by a soundtrack. We found that audiovisual synchrony was a strong determinant of attention when it was embedded in biological motion (two upright animations). However, when biological motion was shown together with distorted biological motion (upright animation and inverted animation, respectively), infants looked at the upright animation and disregarded audiovisual synchrony. Thus, infants oriented to biological motion rather than multimodally unified physical events. These findings have important implications for understanding the developmental trajectory of brain specialization in early human infancy.