<p>Reaching is an important and early emerging motor skill that allows infants to interact with the physical and social world (e.g., when sharing objects). Despite the importance of motor experiences in early infancy, few studies have considered the influence of reaching behavior on cognitive, social, and motor development. In this dissertation, reaching behavior was selectively manipulated in 73 non-reaching three-month-old infants using four different training interventions. Infants' reaching and social cognition skills were assessed and compared, and the long-term effects of one particular training intervention were explored.</p> <p>Of the four training interventions used here, one procedure--referred to as active training--facilitated domain-specific development (reaching and grasping behavior) and increased infants' preferential orienting towards faces in a visual-preference task (face preference). None of the remaining three training interventions facilitated motor development and only one increased face-preference behavior. However, a relation between face-preference behavior and motor experience was present in all trained infants as well as in three- to 11-month-old untrained infants. In untrained infants, face-preference behavior was the earliest social-cognition skill to emerge and was related to later emerging skills such as gaze following. Therefore, a preference for faces may be an important basic social-cognition skill that influences future social development.</p> <p>Additionally, the long-term effects of the active-training procedure were assessed in 14 infants who were tested one year after they had participated in the active-training intervention. Even after one year, converging evidence showed advanced manual exploration and object-engagement skills in trained compared to untrained infants. </p> <p>The studies described in this dissertation attempt to systematically investigate the role of early reaching experiences on subsequent development of motor and social cognition behaviors. The present findings demonstrate the importance of self-produced motor experiences on the development of social cognition and have implications for our understanding of typical development and the etiology of developmental disorders in social cognition.</p> / Dissertation