![]() The nervous system relies on projections that have gone to the wrong place being pruned away when they do not match up as well with the recipient site as projections intended for that site. The sensory areas initially project somewhat globally to the thalamus, so that some nonvisual inputs go to the visual thalamus (the lateral geniculate) and some nonauditory inputs go to the auditory thalamus (the medial geniculate), and conversely some early projections from the visual thalamus go to nonvisual areas, and some early projections from the auditory thalamus go to nonauditory areas ( Bhide & Frost, 1999 Cooper & Cowey, 1990 Frost, 1986 Ramoa & Yamasaki, 1996 D. Once again, when one hand comes down to reach, the hand that was supposed to keep the box raised also comes down, and once again the baby is not able to succeed in retrieving the toy.Īnother example of early lack of precision in neural communication is the underspecification of neuronal projections, earning them the name exuberant projections. In Frame 5, she tries again, once again raising the box with both hands. She is no longer looking through the opening, so she withdraws the hand that had started to reach in (Frame 4). The hand that was supposed to keep the box up fails her, however, and comes down too (Frame 3), creating a problem. Then she lowers one hand to start to reach in for the toy (Frame 2). Cleverly, the baby raises the box with both hands so that she can see in through the opening (Frame 1). The baby needs to be able to see her pacifier through the box opening to succeed in reaching in to retrieve the toy. Such mirror movements of the limbs are not only seen in infants but are normal in children through at least 7 years of age ( Abercrombie, Lindon, & Tyson, 1964 Lazarus & Todor, 1987 Mayston, Harrison, & Stephens, 1999).Ī girl of 7.5 months performing Diamond’s (1990) object retrieval task where the front of the box is open and the toy is on the table near the rear of the box. Here, the command “lower” has gone to both hands, though it was intended for only one hand. That darn lid, though, keeps coming down because when the child lowers one hand, the other hand (the one that should be holding the lid up) comes down as well ( Bruner, 1970 Diamond, 1990 see Figure 1). ![]() Bruner and I independently documented the frustration of infants and toddlers, who having forcefully pushed a lid up with both hands, intend to remove one hand to reach for a treat under the lid. The nervous system command to do the action goes to both hands, lacking the intended precision that was for the command to go to one hand only. For example, when a young child intends to do something with only one hand, there is often motor overflow to the other hand. Developmental psychologists, neuroscientists, pediatricians, and teachers have long known that early in life the nervous system lacks precision in many ways, often functioning in a global, diffuse way.
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