Visual information and object size in infant reaching

It has been suggested that the onset of successful reaching in infants is mediated by the onset of an ability to use sight of the hand to make corrective reaches. However, removing vision of the hand in infants younger than 6 months has not been shown to have an effect on reaching onset or kinematics. We investigated the use of vision of the hand by testing 6-, 9-, and 12-month-old infants reaching for objects in the light and in the dark. We found that infants reached faster in the dark at 6 months, and faster in the light at 1 year. Parallel effects were observed in the movement times. Consistent effects of altering target object size on average speed were seen at 12 months. The data support the hypothesis that vision is used by older infants around 6 months-of-age, and that reach and grasp planning differentiate with object size at about 9 and 12 months-of-age. At younger ages reaches are corrected on the basis of proprioceptive information and sight of the target object.