Early control of reaching: effects of experience and body orientation.

Although research suggests that experience may be a better indicator of the acquisition of certain abilities by infants than age, little work addresses this issue in the development of reaching movements in particular. This longitudinal study fills this gap by verifying the effect of practice time on more- and less-skilled reachers of the same age group in different body orientations. Less- (n=6) and more-skilled (n=4) reachers were evaluated at the acquisition of reaching and again after 1 month of spontaneous practice. Kinematic analyses examined 3D wrist motion during reaching trials in supine (0 degrees ), reclined (45 degrees ) and seated (70 degrees ) orientations. The results indicated that skill level was a relevant factor in dealing with gravitational constraints imposed by different body orientations. Time of practice affected the way less- and more-skilled reachers explored and adapted the kinematic parameters of reaching to constraints imposed by body orientations. These findings suggest that not only age, but also experience and body orientations are important constraints that should be taken into account when examining infant reaching development.