The unspoken part of human communication is present and plays a large role long before the infant can speak. Such an inquiry is forced upon us when we admit that language may be a part of the far larger function of interpersonal communication and relatedness that grows in the child and accompanies us from the cradle to the grave. Human beings understand one another intimately and at many levels. To analyse this ability of persons to act together and to share experience in harmony, we have first to view communication in relation to the private activities of conscious, purposeful action. All voluntary actions are performed in such a way that their effects can be anticipated by the actor and then adjusted within the perceived situation to meet the criteria set in advance.
Interpersonal communication is controlled by feedback of information, as is all voluntary behaviour.
But there is an essential difference between a person doing things in relation to the physical world and the control of communication between persons. Two persons can share control, each can predict what the other will know and do. Physical objects cannot predict intentions and they have no social relationships. For infants to share mental control with other persons they must have two skills. First, they must be able to exhibit to others at least the rudiments of individual consciousness and intentionality.