According to Piaget, the ratio of Egocentric to Social speech is an indicator of cognitive development.
Whatever the experiences are, the more “ticks” that occur, the faster and farther the child will develop cognitively.
The child’s progression along this continuum is somewhat mirrored, according to Piaget, in the context communications which involve either of two kinds of speech--Egocentric and Social
Of course, in the original state of cognition (Autistic) thoughts can not be represented linguistically. Obviously there is no language available at birth.
But to me, even after language has developed, there appear to be personal thoughts which cannot be put into language. This is the eternal draw of the other forms of symbolization such as music, art and dance etc.
By the age of two, however, speech has begun to emerge. Now there becomes a bridge into the mind of the child.