According to Vygotsky, Egocentric Speech is internalized to be come verbal thought.
To Vygotsky, however, egocentric speech was the internalization of speech to become a verbal way of thinking--called language.
But there was one more twist to account for the apparent degeneration of egocentric speech.
Vygotsky explains that we donāt think with a full-blown sentence structure. That would be too cumbersome. Hence, we create our own personal verbal short-hand for our thinking processes. But when someone says, "A penny for your thoughts," we rush to create the full context which we will use to communicate.
The creation of the verbal short-hand begins as the child is internalizing speech to become verbal thought.
This short hand is actually reflected in the egocentric speech of the child and hence, makes it appear to be disintegrating.
NOTES: More information on egocentric speech.
NOTES: Egocentric and Private Speech