Humans and chimpanzees attend differently to goal-directed actions.

Humans comprehend the actions of others by making inferences about intentional mental states of another. However, little is known about how this capacity develops and whether this is shared with other animals. Here we show the ontogenetic and evolutionary foundations of this ability by comparing the eye movements of 8- and 12-month-old human infants, adults and chimpanzees as they watched videos presenting goal-directed and non-goal-directed actions by an actor. We find that chimpanzees anticipate action goals in the same way as do human adults. Humans and chimpanzees, however, scan goal-directed actions differently. Humans, particularly infants, refer to actors' faces significantly more than do chimpanzees. In human adults, attentional allocation to an actor's face changes as the goal-directed actions proceed. In the case of non-goal-directed actions, human adults attend less often to faces relative to goal-directed actions. These findings indicate that humans have a predisposition to observe goal-directed actions by integrating information from the actor.