Organisation of left and right hand movement in a prehension task: a longitudinal study from 20 to 32 weeks.

The organisation of reaching movements was studied longitudinally (every two weeks) in infants aged from 20 to 32 weeks, in order to detect possible differences between the two hands. An object was presented on a table, at a reachable distance, and four trials were retained. Analysis of left and right hand movements was performed, frame-by-frame, on video images obtained from two cameras. Three body points were considered: the elbow, the wrist, and the major finger for drawing the profile of the movement. Three parameters were considered: movement time (MT), straightness, and number of changes in direction. Data show that the right hand MT is always shorter than the left hand MT. Moreover, the right hand is also continuously more directly oriented towards the object and makes fewer corrective changes than the left hand. These data show that a different organisation of movement of the left and the right hand exists early in infancy.