Object use affects motor planning in infant prehension.

The purpose of this study was to investigate the factors underlying the ability to plan object-oriented grasping movements in the first two years of life. In particular, we were interested in evaluating the relationship between manual motor planning, object use and infant-parent interaction. In order to achieve this aim, grasping behaviors of nineteen healthy infants, aged nine to 25 months, were examined during naturalistic play sessions with a standard set of toys. Our main finding was that, regardless of age, infants perform a better manual planning when they use an object in a functional rather than non-functional way, suggesting that the planning of an action also depends on knowing the functional properties of an object. In addition, we found that the ability to use objects in a functional way was strongly affected by infant-parent interaction. Thus, level of object use and environmental role must be taken into account in order to understand the development of manual motor planning.