The child's next task is to divide the flow of language into separate words, and then to understand what the words mean by connecting them with recurring events. Just as in learning a foreign language, we begin to understand the meaning of what someone else is saying long before we are able to put words together into a reply. These internal voices that we remember are the basis for learning how to produce language and communicate with others around us. Much later we learn to recognize written words so that we can translate little squiggles on pages into the sounds of language, and understand books like the one you are reading. If we had no internal voices, we would not be able to understand the words that others say to us, and we would not be able to communicate with words. We would be forever limited to the nonverbal noises, gestures, and movements that we had as infants.

As we learned the particular words and grammar of the language of our parents, caretakers, or others around us, we also learned all the nonverbal musical sounds of their language — the volume, tempo, rhythm, timbre, intonation, hesitation, regional accent, emotional inflection, etc.

For instance, when you hear the voice of a stranger, you can determine with close to 100% accuracy if they are male or female, using these tonal cues — even though you may have no idea what aspects of tonality you are using to do this. And when you answer the phone, usually you can identify who it is by their tonality after hearing only a few words.

Pause right now to remember and listen to the voices of several people you know. Recall them one at a time, and hear the distinct tonality that each one uses. First recall the voice of one of your parents, …