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Two additional behaviors suggest that edges and their movement are important.
When Piaget placed a goblet on a small platform, the child grasped it. Both the goblet’s edges and the platform’s edges were easy to see. When Piaget placed a matchbox on that platform, the child did not pick the matchbox up, unless the platform was tilted and the matchbox slid, exposing both its edges and their movement.
Full myelination of the visual tract, by stabilizing input to V1 in terms of edges and movement, appears to assist transition from Stage 3 to Stage 4 cognition.
What about the Auditory System?
About the age of 4, two things happen.
One, the child’s larynx drops to a position that enables the child’s speech to be understood by a stranger.
Two, the last leg of the auditory system from the thalamus to A1—the auditory radiations—is not fully myelinated until 3 ½ to 4 years of age. So transmission of auditory input to A1 is unstable till then.
Thus far, it appears that A1 cells respond to novel sounds. For example, if a particular sound is repeated 90 % of the time and another sound 10% of the time, the rare sound will activate A1 cells more—that is, their firing rate will be greater—whether the rare sound differs in frequency or loudness.
Also, an A1 cell that responds most to a particular frequency, also responds to a rate of change in frequency. An A1 cell, which is characteristically activated by a low frequency sound, is also activated by a frequency that is increasing. And, an A1 cell, which is activated by a high frequency sound, is also activated by a frequency that is decreasing.
At about 3 ½ to 4 years of age, the child is still in the Preconceptual Phase (age 2-4). In the Preconceptual Phase, the child does not understand the difference between aslug and theslug. Piaget’s daughter referred to two slugs 10 yards apart as theslug. Similarity of shape—an attribute—is sufficient to define an object. A slug—as a member of the class of slugs—has no meaning for her.
However, when the auditory tract from the ear to A1 is fully myelinated, bits of word-sounds—frequency, direction of change in frequency, novelty of either frequency or loudness—selectively and reliably activate A1 cells. And, in turn, these parts of sound will stably activate the schemes or circuits that are downstream from A1.
Although the child has been using word-sound schemes or circuits for quite awhile, now—with full myelination to A1—bits of word-sound schemes corresponding to aslug and theslug as well as to long, longer and longest are stably distinct. She has stable a, the, er, est and other extensions of words as parts of her word-schemes to work with, as she interacts with and listens to adults and older children.
At the same time, because her larynx has dropped, she can also listen to, and adjust the bits of her own adult-like word-sounds.
The stable bits of auditory circuits should help her move into the Intuitive Phase, during which she begins to understand nuances of language that deal with attributes of objects—attributes such as color, length, and amount.
For example, if she is asked to put the things together that go together, she may separate red objects from blue objects. If asked if there is another way to group the objects, she may fail to sort by size or shape. Her understanding that attributes may be used to classify objects is incomplete—unsophisticated. But it has begun.
Also an Intuitive-Phase child will arrange sticks according to length for awhile. So she has a notion of seriation.
She thinks that the car that finishes first is the faster car, regardless of the route taken. She is mistaken, although if a car gets there first, often it is faster. She has begun to understand seriation of attributes.
Full myelination of the auditory tract stabilizes the transmission to A1 of impulse patterns that correspond to distinct bits of word-sounds. In turn, the portion of a scheme for a slug and the slug is reliably distinct as the child listens to and interacts with adults and older children as well as listens to her own adult-like speech. Such interactions should assist a child’s beginning understanding of classification, provided that she is in a culture that has a language that supports classification as a way of viewing the world. Similarly, distinct portions of schemes that correspond to words such as long, longer and longest should assist the child’s beginning understanding of seriation.
To sum up: I have shown how full myelination of the visual tract, at about 6 months, would assist transition to Stage-4 cognition, and how full myelination of the auditory tract, at about the age of 4 years, would assist transition to Intuitive-Phase cognition.
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