Studies on the Development of Motor Function in Infancy

This study of 1230 infants and newborns was undertaken to realize the development of motor activity. Followings are the results obtained.(1) The percentage of the infants who had acquired the activity arised with the monthage advanced, increasing its value rapidly near the point at which median infants had acquired the activity. And it became a slow increase after that point, showing this tendency more obviously in the higher stages of motor development.(2) The harder became the behavior to achieve, the longer were needed the periods during which the percentage of the infants who had acquired the activity came to 100% from 50%, for there were the infants who acquired the activity extremely late for their chronological age. This fact suggests that the motor development is affected by the physical and environmental components.(3) No remarkable differences were observed in the period at which 50% of the infants had acquired the activity comparing with the pre-war babies.(4) No sexual differences were observed in the period at which 50% of the infants had acquired the activity