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Consider the visual system.
The last leg of the visual system, from the thalamus to V1, is not fully myelinated until sometime in the 4th or 5th month after birth. From what I Just explained about myelination of neural tracts, it follows that transmission of visual input to V1 is unstable till the 4th or 5th month.
From tne work of Hubel and Weisel, it has been known that, if an edge of light is cast on the retina, certain V1 cells will be activated—they fire a burst of electrical impulses. If the orientation of an edge of light differs by 15 degrees, those V1 cells will not be activated, but others will, and so on around the clock.
Also, if a light moves across the retina in a particular direction, certain other V1 cells will be activated. If the light moves in a different direction still other V1 cells will be activated.
To repeat, depending on the orientation of edges of light and the direction of their movement, different sets of V1 cells will be selectively active. In turn, depending on edges and movement, the NEURONAL CIRCUITS that are downstream from the V1 cells will also be selectively activated.
It should be noted that the single best indicator of an object is movement of its edges as a set. However, this selectivity of visual input, in terms of edges and movement, will be unstable—until the visual tract is fully myelinated, which as I said will not take place until the child is almost 6 months old. Six months of age is in the last few months of Piaget’s Stage 3 of the Sensorimotor Period.
In these last few months of Stage 3, when a visual scheme (a visual neuronal circuit) and a striking scheme (a somatosensorimotor circuit) are both active, if the visual scheme includes activation by edges and movement that belong to an object, the relationship between the two schemes should tend to be successful. By successful, I mean striking should tend to cause an object to bounce.
Similarly, when both a grasping scheme and a visual scheme are active, if the visual scheme includes activation by particular edges and movement, the child should be increasingly successful at grasping an object.
Such successes are common in Piaget’s Stage 3.
Then in Stage 4 (8-12 mo.), schemes of objects are more distinct from one another. The child knocks one object aside in order to grasp another, and searches under the edges of screen for a fully hidden object.
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