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 fluctuations were present in infants' spontaneous, nonreaching, and freely performed movements. We collected reaching and nonreaching movements kinematics in 4 infants that we followed longitudinally during their 1st year. In their 4th year, we assessed the direction of their hand preference. We found that lateral biases in spontaneous, nonreaching movements in the 1st year showed several shifts that were similar to those observed in reaching. Despite these shifts, all 4 infants traversed a short period of right-handedness. This right-handedness matched the direction of their hand preference at 3 years 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.