The fact that humans talk to themselves, especially in difficult circumstances, has been observed by scholars since the Middle Ages. Writings on self-communication have been documented in virtually every epoch of human history since that time. However, in the 20th century, psychologists such as Jean Piaget and L. S. Vygotsky have paid close attention to this mode of communication as they formulated their respective theories of human development. Vygotsky in particular assigned Intrapersonal Communication Theories 567 intrapersonal communication (IC) special status within his developmental theory, and this perspective forms the basis of the following discussion.

According to Piaget, whose theory of human development is grounded in biological mechanisms, at around the age of 3, children begin to display what he called egocentric speech—speech directed at no one other than themselves—as they engage in various kinds of play activities. Piaget referred to IC as egocentric because he believed that children at this age are heavily focused on themselves as individuals and have not yet developed into social beings. As they become less egocentric and more social, this form of speech dies away, leaving social speech as the primary form of human communicative activity.

Vygotsky, on the other hand, adopted a social orientation to human thought, arguing that mental activity is derived from social, or interpersonal, interaction between children and other members of their sociocultural community. He reasoned that egocentric speech does not emerge from egocentric thinking in children but represents instead a stage in the transition from social to inner speech (i.e., speech no longer social in function that is also shed of its linguistic form, leaving a residue of pure meaning), which serves to complete the thinking process. Thus, egocentric speech is simultaneously quasi-social and quasi-psychological speech; while it may appear to be social in form, it gradually takes on psychological functions. Early in life, children frequently engage in activities more or less spontaneously, without the benefit of planning. Hence, they create drawings and, after the fact, decide what they depict. As children mature, however, they begin to use speech to plan what it is they will draw before realizing the plan in a concrete drawing. When this occurs, speech becomes fully psychological. The planning process may be carried out, in part at least, in vocalized language, or it may remain hidden from observation as inner speech.

Source : Littlejohn, Stephen W and Karen A.Floss. (2009). Encyclopedia of Communication Theory.USA:SAGE. 635-636