How hands shape the mind : The P400 as an index of manual actions and gesture perception

Being able to perform and understand actions is crucial for proper functioning in the social world. From birth, we use our bodies to act and to promote learning about ourselves, our environment and other people’s actions and intentions. Our mind is embodied; thus, our actions play a crucial role in cognitive and social development. This thesis focuses on the close interrelation between action and perception and the role of our hands in this link. Three empirical studies on action processing are presented in a framework of embodied cognition that emphasises the role of bodily experience in social development. All three studies were designed to measure event-related potentials (ERPs) in infants 4 to 9 months old, when they observed manual actions, grasping and the give-me gesture. Study I demonstrates the neural underpinnings of infants’ action–perception link at the age when their ability to grasp for objects in a functional manner emerges. Neural processing has been found to be influenced by infants’ own manual experience of exactly the same grasping action. Study II reveals that brief active motor training with goal-directed actions, even before the solid motor plans for grasping are developed, facilitates processing of others’ goal-directed actions. Study III shows that the same neural correlate that indexes processing of reaching actions is involved in encoding of the give-me gesture, a type of non-verbal communication that conveys a request. This ability was found not to be directly dependent on the infants’ own ability to respond behaviourally to another person’s gesture. This thesis pinpoints the neural correlate, P400, involved in the processing of goal-directed actions and gestures. The findings highlight the importance of motor experience, as well as the involvement of attentional processes in action processing. Additionally, the data from Study III may suggest a possible involvement of grasping skills in encoding non-verbal communicative gestures