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LANGUAGE DEVELOPMENT AS A BASIC RESEARCH TOPIC

A child who has acquired language has acquired an incredibly complex and powerful system. If we understood how children accomplish this task, we would know something substantial about how the human mind works. The modern field of language development emerged in the 1950s when it became clear that language acquisition would serve as a test for rival theories of how change in human behavior occurs (H. Gardner, 1985; Pinker, 1984). In the 1950s, two psychological theories were pitted against each other: behaviorism and cognitivism. According to behaviorism, change in behavior occurs in response to the consequences of prior behavior. Most readers are familiar with clear examples supporting this view. For instance, rats that initially do not press levers come to press levers after receiving food pellets for producing behaviors that increasingly approximate lever pressing. Radical behaviorism holds that all behavior can be accounted for in this way. A central tenet of behaviorism is the belief that it is not necessary to discern what goes on in the mind of the rat in order to explain the change in the rat's behavior; behavior can be fully accounted for in terms of things external to the mind.

Cognitivism asserts the opposite -- that we cannot understand behavior without understanding what is going on inside the mind of the organism producing the behavior. From approximately 1930 to the early 1950s, behaviorism dominated American psychology. But in the 1950s, a "cognitive revolution" began (H. Gardner, 1985). During the next two decades, behaviorism came to be seen as inadequate, and the focus of the search for explanations of human behavior shifted to internal mental processes. Studies of language played a crucial role in the cognitive revolution. The ability to speak and understand language is incredibly complex, and children acquire that ability without receiving positive reinforcement for successive approximations to grammatical sentences. Simple theories that may well explain why rats push levers, why dogs salivate at the sight of the people who feed them, and why humans get tense when they sit in the dentist's chair cannot explain how children learn to talk. When cognitivism displaced behaviorism, theoretical dispute concerning how to understand human behavior did not end. In fact, a new interdisciplinary field called cognitive science emerged from the cognitive revolution.

Cognitive scientists now agree that it is necessary to understand how the mind works in order to explain human behavior, but they do not agree on how the mind works. The study of language acquisition still plays a central role in the debate over how to characterize human cognition, for the same reason that language acquisition played a central role in the cognitive revolution. That is, it is so difficult to explain how language acquisition is possible that accounting for language acquisition is a test not likely to be passed by inaccurate cognitive theories. Language acquisition is the New York City of the field of cognitive science: If you can make it there, you can make it anywhere.

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NORMATIVE STUDIES

In the period between the end of World War I and the 1950s, the goal of most research on language acquisition was to establish norms (Ingram, 1989). Toward that end, several large-scale studies were undertaken to provide data on when children articulate different sounds, the size of children's vocabularies at different ages, and the length of their sentences at different ages. Consonant with the behaviorist orientation of the times, the goal was not to ask theoretical questions about either the nature of humankind or the nature of language development but simply to describe what could be observed. These older studies are still valuable as descriptions of normative development (e.g., McCarthy, 1930; Templin, 1957), and as new instruments for assessing children's language are developed, new normative studies continue to be conducted (e.g., Fenson et al., 1994).

THE CHOMSKYAN REVOLUTION

In the 1960s, the study of children's language development changed radically. The catalyst for this change was the 1957 publication of a slim volume entitled Syntactic Structures, written by Noam Chomsky, then a young linguist at the Massachusetts Institute of Technology. That piece, along with Chomsky's subsequent prolific work, revolutionized the field of linguistics and, within a few years, the study of language development. Before Chomsky's work, linguists concentrated on describing the regularities of languages. Linguists could study their own language or, better yet, a little-known language, but the job was the same: to find the patterns in what speakers do. Chomsky caused a revolution by saying that what speakers do is not as interesting as the mental grammar that underlies what speakers do. Since Chomsky's writings, the work of linguists consists of trying to describe what is in the minds of speakers that explains how speakers do what they do.

That new goal of linguistics raised a question about children. If adults have a mental grammar that explains what they do when they talk, then children must have a mental grammar that explains what children do. Children's speech is different from adults' speech; therefore, children's mental grammars must be different. What are children's grammars like, and how do children eventually achieve adult grammars?...

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IS IT NATURE OR NURTURE?

Is the development of language in children the result of human's innate endowment (like the development of upright posture and bipedal locomotion), or is it the result of the circumstances in which children are nurtured (like the development of table manners or the ability to do calculus, both of which depend on particular experiences)? This is the nature-nurture debate, and it predates not only the modern study of language development but also the emergence of psychology as a discipline. This was the ongoing debate, when the wild boy of Aveyron left the woods in 1800. The extreme experience-based position, known as empiricism, asserts that the mind at birth is like a blank slate; all knowledge and reason come from experience (J. Locke, 1690). The alternative view, known as nativism, asserts that knowledge cannot come from experience alone. The mind must have some preexisting structure in order to organize and interpret experience (H. Gleitman, 1995; Pinker, 1994; see the works of Plato and Kant for the original arguments). This debate still rages among those who study language development.

THE NATIVIST VIEW

For proponents of nativism as an explanation of language development, there are three salient "facts" about language development: (1) Children acquire language rapidly, (2) children acquire language effortlessly, and (3) children acquire language without direct instruction. Rapid, effortless, untutored development seems more like maturation than like learning in the usual sense of the term. As Chomsky (1993) put it,

Language learning is not really something that the child does; it is something that happens to the child placed in an appropriate environment, much as the child's body grows and matures in a predetermined way when provided with appropriate nutrition and environmental stimulation. (p. 519)

The modern-day descendant of the opposite, empiricist view is behaviorism. As mentioned earlier, behaviorism has not stood the test of time (or empirical evidence) as a theory of language acquisition. Behaviorist theories wil1 be mentioned again in the following chapters, but primarily for historical completeness.

THE INTERACTIONIST VIEW

In current debate, the alternative to nativism is not pure empiricism but rather interactionism (Braine, 1994). Like nativists, interactionists acknowledge that there must be some innate characteristics of the mind that allow it to develop language based on experience. But the interactionist position places a greater burden of accounting for language development on the nature of children's language-learning experiences than the nativist position does. Research on the nature of the language input children receive and the relation of that input to the rate and course of development are relevant here (see, e.g., Gallaway & Richards, 1994; Hoff-Ginsberg & Shatz, 1982; Morgan, 1990). The position known as social interactionism holds that a crucial aspect of language-learning experience is social interaction with another person. lnteractionists contest the "facts" so salient to the nativists. As Catherine Snow put it,

We on the other side think that learning language is a long slog, which requires from the child a lot of work. And the child is working as hard as he can, fifteen, sixteen hours a day. We think it requires a relationship with an adult, and a whole set of cognitive abilities. (quoted in Rymer, 1993, p. 37)

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Another term for this type of position is constructivism. Constructivism as a view of development was first argued with respect to cognitive development by Jean Piaget, and constructivism remains a term in current use. According to the constructivist view, language (or any form of knowledge) is constructed by the child using inborn mental equipment but operating on information provided by the environment. In 1975, Noam Chomsky and Jean Piaget debated their respective nativist and constructivist views of language development at the Abbaye de Royaumont near Paris. Nearly 200 years after the wild boy of Aveyron left his woods (and roughly 200 miles away), the debate about the essential nature of the human mind continued. In his foreword to the edited transcript of that debate, Howard Gardner (1980) summarized the two views:

Piaget saw the human child -- and his mind -- as an active, constructive agent that slowly inches forward in a perpetual bootstrap operation, Chomsky viewed the mind as a set of essentially preprogrammed units, each equipped from the first to realize its full complement of rules and needing only the most modest environmental trigger to exhibit its intellectual wares. (p. xxiii)

The term emergentism has been used to label the view that knowledge can arise from the interaction of that which is given by biology and that which is given by the environment (MacWhinney, 1999). This term tends to be used in the context of models of learning that are termed connectionist, parallel distributed processing, or neural network models (Bates & Goodman, 1999). The advent of these learning models has given new life and new form to the old nature-nurture debate. As Bates and Goodman (1999) put it, "the debate today in the field of language development is not about nature versus nurture, but about the 'nature of nature'" (p. 33). That is, granting that there must be some innate characteristic of the human mind that allows language development, theorists still disagree about the nature of that which is innate.

WHAT IS THE NATURE OF NATURE?

There are different ways that something can be innate (Elman et al., 1996). The most strongly nativist view holds that knowledge itself is innate. A weaker form of innateness holds that the computational procedures for learning are innate and that knowledge results from the way in which those procedures operate on input. According to the innate knowledge view with respect to language acquisition, children have inborn knowledge of the general form of language, and it is this inborn, specifically linguistic knowledge that allows children to figure out a whole language in only a few years. Thus, this theoretical position holds that the internal contribution to language is in the form of domain-specific capacities. Various contrasting views differ from this position both in putting more burden on the input and learning procedures and in questioning the domain specificity of the internal (i.e., innate) contribution to language acquisition.

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IS INNATE GRAMMAR NECESSARY?

Most of the arguments for grammar's innate basis are not arguments based on evidence for such a genetic basis. Rather, the argument holds that general learning mechanisms are too weak to accomplish the acquisition of grammar and that regardless of the learning mechanism, the speech that children hear is inadequate to support the acquisition of grammar. Thus, grammar must be innate because there is no way to learn it. The argument that input is inadequate was made first by Noam Chomsky and is known as the poverty of the stimulus argument. The stimulus is the speech that children hear, and its poverty is its inability to support the acquisition of grammar. There are two aspects to the poverty of the stimulus argument. One is the assertion that it is impossible, in principle, for children to figure out the generative system underlying language just from hearing examples of sentences. The other is Chomsky's claim that the speech children hear is full of errors, false starts, slips of the tongue, and so on, giving children a very bad database from which to work.

These claims that support the contention that grammar must be innate have been countered, although the adequacy of the counterarguments is disputed. The assertion that cognitive mechanisms are inadequate has been countered with proposals of how general cognitive mechanisms could achieve aspects of grammatical knowledge and with evidence that general cognition does contribute to grammatical development. These arguments also often involve some definition of the nature of the adult language that children eventually achieve. The assertion that the input is inadequate has been countered with evidence that the speech children hear is not so impoverished as Chomsky had supposed and that it does play a significant role in grammatical development.