Stage 2 also introduces the concept of active or working memory, which is defined by the occurrence of consciously controlled information processing activities. Working memory is a limited memory that can be easily overloaded (e.g., attending to two or three things at once is difficult -- if not impossible). Many of the information processing activities the person acquires will be techniques to overcome active memory limits (e.g., repeating information to oneself keeps the information in active working memory until it can be applied). The "stage" aspect in cognitive development shows itself by the ability of the infant to attend to information selectively. This is a cognitive capability which, once developed, is a permanent feature of cognition that distinguishes the stage 2 child from the stage 1 child.

Stage 3 represents the development of language processes out of earlier processes and knowledge stored in long-term memory. In developing oral language, the listening process is used in attending to spoken language to learn the words and grammar of language. Thus, listening plus languaging, occurs simultaneously. This joint occurrence is given the special name of auding. On the production side, the joint occurrence of uttering (making sounds through the mouth) with the production of word forms from the language pool, and stringing the word forms together to make sentences using the rules of grammar, produces the special process called speaking. Auding and speaking comprise the oral language information reception end production skills. Speaking is used to represent information that the person has in his or her mind "outside the head" and in the acoustic medium, while auding is used to pick-up and transform speech information displays into knowledge in the mind of the listener. To an observer, the stage 3 child can respond to and produce oral language, at least to some minimal degree. Again, as with conscious attending, once oral language has begun to emerge, the cognitive system is permanently modified (barring physiological trauma of some sort), and the person is no longer capable of exclusively prelinguistic modes of thought.

In transitioning to stage 4, the information processing skills of looking and marking are used to learn a representational system which, in many respects, represents the spoken language in a different medium light, and in a more or less permanent graphic display: the written language. Looking at written language and transforming the written language into meaning is called reading. Writing is the special use of marking skills to produce graphic language (and other symbols and symbol systems).

In the typical case, people develop a fair amount of competence in oral language before they are exposed to formal instruction in reading in elementary grades (though informal learning of literacy may begin in the home and community in literate cultures). Written language skills build upon the earlier developed oral language skills and add new vocabulary and concepts, as well as special knowledge about how to represent information in the graphic medium, to the person's knowledge base. In turn, learning new vocabulary and conventions of language through reading and writing enlarges the person's oral language abilities. The large arrow at the far right in Figure 2 is meant to represent the notion that the development of oral and written language ability may continue indefinitely as the person studies and develops new knowledge domains.

A major component of Figure 2 is the person's long term memory or "knowledge base" discussed above as a part of the human cognitive system. The long term memory contains all the knowledge developed by the person in interaction with the environment. Much of the knowledge acquired by the person will not be understood in consciousness (for example, the rules of grammar). Rather, it will be unconsciously used to accomplish tasks such as developing language competence and comprehending the events of the world. In addition to the general world knowledge and processes that are in the mind, though not necessarily accessible to conscious understanding without considerable analysis, the memory also contains the language knowledge (words and grammar) that can be used to represent information that arises from experience in the world (e.g., bodies of knowledge about machines, parts of the body, houses, neighborhoods -- sometimes called "schema" or "mental models") and from didactic instruction, as in training programs (Sticht, 1992).