Lateral biases and fluctuations in infants' spontaneous arm movements and reaching

The development of hand preference in infant reaching is marked by several lateral fluctuations. This study investigated whether similar lateral fluct uations were present in infants' spontaneous, nonreaching, and freely perfo rmed movements. We collected reaching and nonreaching movements kinematics in 4 infants that we followed longitudinally during their 1st year. In thei r 4th year we assessed the direction of their hand preference. We found tha t lateral biases in spontaneous, nonreaching movements in the 1st year show ed several shifts that were similar to those observed in reaching. Despite these shifts, all 4 infants traversed a short period of right-handedness. T his right-handedness matched the direction of their hand preference at 3 ye ars of age. We propose that shifts in the development of hand preference in the 1st year are linked to successive reorganizations of the motor system. These reorganizations take place as infants learn to sit, crawl, and walk. (C) 1999 John Wiley & Sons, Inc.