Do infants apply the principle of rational action to human agents?

Twelve- to fourteen-month-old infants' reactions to violations of the principle of rational action [Cognition 56 (1995) 165] were studied in two experiments, using humanlike puppets and human agents rather than computerized shapes as stimuli. In Experiment 1, infants watched a puppet approaching another puppet on a stage, while in Experiment 2 a videotaped sequence of a person approaching another person was shown. In both experiments, a rational and a non-rational approach condition were contrasted in the habituation phase. In the rational approach condition, an obstacle had to be overcome by climbing or jumping. In the non-rational approach condition, the agent made a detour approach in the absence of an obstacle. In the test phase, infants watched direct and indirect-approach events. In both experiments, infants in the rational approach condition looked significantly longer at indirect-approach than at direct-approach test events, while no difference between the two types of test events was observed in the non-rational approach condition. These findings support the assumption that one-year-old infants have principled expectations about rational goal approaches of human agents. (C) 2004 Elsevier Inc. All rights reserved.