Using various methods, we have shown that infants as young as 9-12 months of age understand not just others’ goals but also their intentions, the action plans they choose to achieve their goals. Similarly, 1-year-olds understand not just others’ perception but also their attention, that is, they know which particular object or aspect of an object others are focusing on within their visual field. We have found that 1-year-olds even understand others’ knowledge/ignorance, in the sense of what objects or events others have experienced in the past. However, even much older children have difficulty taking others’ visual perspectives. We have investigated under what conditions infants know what others know and can see from a perspective different from their own. We have found that sharing experiences with others in joint attentional engagement facilitates young children’s understanding of what others know, but hinders children’s understanding of what others can see. We have also shown that 3-year-olds know that two people can have mutually incompatible desires, and that this understanding is related to executive function. And using various new nonverbal methods, we studied 1-year-old infants’ understanding of others’ false beliefs.
Our general findings are that great apes and human infants are fairly similar in their understanding of others’ intentional states, but human infants go beyond apes in their skills and motivations for sharing intentions in such things as collaborative activities and cooperative communication.