The previous studies have shown that human infants and domestic dogs follow the gaze of a human agent only when the agent has addressed them ostensively—e.g., by making eye contact, or calling their name. This evidence is interpreted as showing that they expect ostensive signals to precede referential information. The present study tested chimpanzees, one of the closest relatives to humans, in a series of eye-tracking experiments using an experimental design adapted from these previous studies. In the ostension conditions, a (...) human actor made eye contact, called the participant’s name, and then looked at one of two objects. In the control conditions, a salient cue, which differed in each experiment (a colorful object, the actor’s nodding, or an eating action), attracted participants’ attention to the actor’s face, and then the actor looked at the object. Overall, chimpanzees followed the actor’s gaze to the cued object in both ostension and control conditions, and the ostensive signals did not enhance gaze following more than the control attention-getters. However, the ostensive signals enhanced subsequent attention to both target and distractor objects (but not to the actor’s face) more strongly than the control attention-getters—especially in the chimpanzees who had a close relationship with human caregivers. We interpret this as showing that chimpanzees have a simple form of communicative expectations on the basis of ostensive signals, but unlike human infants and dogs, they do not subsequently use the experimenter’s gaze to infer the intended referent. These results may reflect a limitation of non-domesticated species for interpreting humans’ ostensive signals in inter-species communication. (shrink)

In this review, we discuss the implications of placing an infant in the supine position with respect to human cognitive development and evolution. When human infants are born, they are relatively large and immature in terms of postural and locomotor ability as compared with their closest relatives, the great apes. Hence, human mothers seemingly adopt a novel pattern of caring for their large and heavy infants, i.e., placing their infants in the supine position; this promotes face-to-face communication with their infants. (...) Moreover, infants in the supine position can interact with other nearby individuals in the same manner from an early age. In addition, the infants can also explore their own body parts and/or objects with their hands since the hands are not required to support the body and are therefore, free to move. These activities are considered to be fundamental to the early development of human social and nonsocial cognition, including knowledge of self, in the first six months after birth. Further, developmental continuity in the voluntary exploratory movements in the prenatal period to the early postnatal period is also discussed. (shrink)