Throughout our daily lives, we frequently observe other people carrying out various actions. How do we process these actions and come to understand the goals and intentions of the people that we are watching? Historically, the brain systems underlying the perception of an action and the actual carrying out of an action have often been considered to be quite separate, but recent research has suggested substantial overlap. One recent theory suggests that recognizing and understanding an action involves brain systems that would be involved in carrying out the same action--the "mirror neuron system" (MNS). On that theory, in order to understand someone else's actions, our own brains actually covertly mirror that person's actions. The MNS was originally identified in monkeys, and recent work has suggested that a similar system also exists in humans. However, one key aspect of the MNS that is relatively unexplored is the development of the coupling between the perception and action systems during action observation. With support from the National Science Foundation, Drs. Peter Marshall and Thomas Shipley at Temple University are carrying out a series of studies designed to elucidate the development of the MNS. The studies involve infants, preschoolers and adults participating in different tasks which are designed to assess the overlap between the perception and action systems during action observation. These tasks include the passive viewing of human actions, the recognition of oneself performing an action, and the imitation of novel actions. During some of the tasks, the electroencephalograms (EEG) will be recorded. In combination with analyses of participants' overt behavior during these tasks, it will be determined whether motor areas of the brain are indeed active while infants and children observe human actions. The research will also investigate how this brain activity relates to other behavioral measurements of the coupling between perception and action, and how the patterns of brain activity relate to young children's abilities to understand and copy the actions of others. The studies involve the active participation of undergraduate and graduate students at all stages of the research process. They have clear potential for being broadcast to professionals and laypeople interested in how children and adults process and understand other people's actions. The result may help us understand pervasive developmental disorders such as autism, which are characterized by deficits in imitation and social cognition and which may involve disruptions in MNS function.