In other words, the primary object of each of the various centres involved is not speech, but some other and simpler function; and speech arises by development from a union of these separate functions.
4.

In observing young children, a more direct application of experiment is possible.

By "experiment" here I mean both experiment on the senses and also experiment directly on consciousness by suggestion, social influence, etc.

In experimenting on adults, great difficulties arise through the fact that reactions--such as performing a voluntary movement when a signal is heard, etc .-- are complicated by deliberation, habit, custom, choice, etc.

The subject hears a sound, identifies it, and presses a button--_if he choose_ and agree to do so.