Developmental Precursors to Active Maintenance

Visual perception is constantly challenged by visual occlusion: objects in our environment constantly obscure one another, and seem to "disappear" when in fact they are nonetheless present.

Young infants begin to demonstrate a basic understanding of "object permanence" at some point during the first six months of life. On more complex tasks, understanding of object permanence is not observed until months later, as in Piaget's A-Not-B task. Even in these more demanding tasks, however, some understanding of object permanence can be revealed by the direction in which children gaze: kids will look in the correct location even as they search for the occluded object in a more familiar but incorrect location.

Work from Linda Smith and colleagues has revealed other ways in which A-Not-B task performance is "effector-dependent." Changing proprioceptive input to the brain between the reaches to the first and second locations - by adding weights to the infant's arms - improves performance. Similarly, performance is improved when children go from standing to seated (or vice versa) in between the reaches to the first and second locations.

As argued by Smith and colleagues, the apparent effector-dependence of the A-Not-B task does seem to reflect the centrality of the motor system at this stage of development (or as they call it, "embodiment.")

Why should a (putative) test of "object permanence" be so strongly effector-dependent?