Vision for action in toddlers: the posting task.

Three experiments examine 18- to 24-month-old (N = 78) toddlers' ability to spatially orient objects by their major axes for insertion into a slot. This is a simplified version of the posting task that is commonly used to measure dorsal stream functioning. The experiments identify marked developmental changes in children's ability to preorient objects for insertion, with 18-month-olds failing completely and 24-month-olds succeeding easily. In marked contrast, 18-month-olds preorient their empty hands for insertion into the same slots. This developmental dissociation between aligning hands and aligning objects to slots suggests that the key developmental change is in action with the goal of object-to-object alignment versus action on an object.