The control of reaching movements by young infants

Samples of reaches were obtained from groups of infants aged 4.5, 6, and 7.5 months. Split-screen video recordings were transcribed as sequences of (x,y,z) hand coordinates, and the hand path was examined for evidence of initial aiming and subsequent correction of the movement path. At all ages, the initial direction of the movement was correlated with target direction, providing evidence that the hand was aimed toward the target. Additionally, changes in movement direction made after the commencement of the movement tended to curve the hand path toward the target, providing evidence of error correction. Local minima of hand speed evident within segments of continuous motion were associated with turn toward the target. However, the movement path was also curved toward the target within the movement elements bounded by these minima. This finding was seen as consistent with "continuous" correction of movement errors and as contrary to the suggestion that infant movements are concatenations of ballistic movement units whose boundaries are marked by troughs in the speed profile.