Proximodistal structure of early reaching in human infants

Nine infants were tested, at the age of onset of reaching, seated on their parent's lap and reaching for a small plastic toy. Kinematic analysis revea led that infants largely used shoulder and torso rotation to move their han ds to the toy. Many changes in hand direction were observed during reaching , with later direction changes correcting for earlier directional errors. A pproximately half of the infants started many reaches by bringing their han ds backward or upward to a starting location that was similar across reache s. Individual infants often achieved highly similar peak speeds across thei r reaches. These results support the hypothesis that infants reduce the com plexity of movement by using a limited number of degrees-of-freedom, which could simplify and accelerate the learning process. The proximodistal direc tion of maturation of the neural and muscular systems appears to restrict a rm and hand movement in a way that simplifies learning to reach.