Changes in reaching and grasping objects of different sizes between 7 and 13 months of age

Twenty-four 7- to 13-month-old infants were videotaped when grasping or attempting to grasp objects of different sizes ranging in height from 7 to 17..5 cm. We investigated how early during the action sequence young infants use their two hands to grasp large objects, in order to determine the age at which they anticipate the need for a bimanual strategy from perception of object size. Second hand onset was also measured to examine whether the second hand could be recruited at any time during an action. The results show that most movements start unimanually and that the second hand is activated later The younger infants were more successful when grasping large objects with two hands than with one hand, but they did not show more bimanual reaching with large as compared to small objects before 11 months of age. These findings suggest that young infants do not perceive the same action relevant information to drive an action as older infants and that infants shift from a correction to an anticipation strategy as they grow older. The results fit with the idea that, regarding features like size, relevant visuomanual experience may be important for full coordination of the constituent perceptual and motor skills. In addition, after a unimanual initiation, the younger infants tended to activate their second hand only after the first one had completed its course. In contrast, more intermanual flexibility was observed in the older infants. This reflects an increasing range of coordinated patterns during bimanual actions around the end of the first year of life.