In the first 18 months or so, the infant's learning consists of developing and coordinating his actions and perceptions into organized action or sensori-motor schema. Piaget views the infant's mental life as beginning with an undifferentiated world. Gradually the child begins to distinguish himself from other persons and objects. He shows through his actions, after some progress, that he has learned that objects still exist when outside his perceptual field. He learns to recognize objects and develops some bases for conceptualizations of location. Later he is able to distinguish an action from the object of that action. He develops an ability to anticipate actions from various signs that later lead to the formation of conceptualizations of causality. These and many other achievements result in what Piaget calls sensori-motor intelligence, which, although not innate, is said to occur universally.

The child at the end of this sensori-motor stage can in some sense understand the concepts of agent, action, object, location, cause, and so forth, and has some notion of the possible relations among these. As discussed in the previous section, these are the basic elements in some of the current models of the adult's conceptual base.

Brown (1973) believes that Piaget's work provides a basis for the acquisition of spoken language. He writes: "I think that the first sentences express the construction of reality which is the terminal achievement of sensori-motor intelligence" (p. 200). Brown distinguishes three levels preceding the verbal expression (oral languaging) by the child of any part of his "construction of reality" (p. 152):

1. The sensori-motor pattern itself is a form of action in the world.
2. The ability to represent or think about the pattern without necessarily intending to speak about it (ie., conceptualizing).
3. The semantic intention to make a sentence expressive of the pattern.

The types of utterances children produce, and what they actually seem to express, will be discussed later. What is important for now is the point that, in the present model, cognitive content in the form of a conceptual base develops prior to the ability to language, via the sensori-motor information-processing activities of listening, looking, uttering, and marking (or otherwise manipulating the external environment).