LANGUAGE ACQUISITION AND DEVELOPMENT
John Hughlings Jackson wrote, "No child would ever talk unless he were taught; and no child could be taught unless he already possessed, by inheritance, a particular series of nervous arrangements ready for training" (Marshall 41). It is amazing how natural language acquisition is for children: "Language development does not begin with the child’s first efforts to learn material that is linguistic" (Locke 268). Children are ready to learn even before birth: some acquisition of language, such as vocal learning, begins as early as the final trimester of pregnancy (Locke 267).
Language development begins with the infant’s inclination to attend and respond to certain aspects of talking behavior. Genetic factors seem to play an important role: the infant’s responsiveness to facial and vocal activity is presumed to be heavily influenced by genetic factors. Specific neural preadaptations underlie such behavior: Clinical and electrophysiological research reveals that humans have mechanisms that are similarly dedicated to processing faces and facial activity (Tranel, Damasio and Damasio, 1988 as quoted in Locke) and to voices and vocal activity (Creutzfeldt, Ojemann, and Lettich, 1989 as quoted in Locke).
These examples of specialization in of social cognition are important in language development. Tomasello and his colleagues (1986, Locke 269) found a positive relationship between the amount of time infants participated in joint attention episodes with their mothers at 15 months and extent of expressive vocabulary at 21 months. Snow (1989, Locke 269) found that vocal imitation at 14 months was related to the number of nouns and verbs produced, the total productive vocabulary, and the ratio of words produced to words comprehended at 20 months. Such evidence supports Chomsky’s view of the existence of deep internal structures associated with language acquisition.
Another fascinating fact is the fast rate at which children acquire language. The table below (adapted from Kandel) points out that in children 12-18 months old, the vocabulary is about 30 to 50. In children 18-24 months, the vocabulary is about 50 to several hundred (which means, in about six months the vocabulary more than doubled). When the child starts to walk at three years old, he has vocabulary of around 1,000 words. This means that, in a little more than a year, a child gains around nine hundred words—about 25 words a day!
Children do not have to learn to correct many of their mistakes, for some errors never happen. When an error is made and corrected, it is a logical error with respect to the usual syntactic structure (Danchin 32). In other words, children do not repeat mistakes which must be corrected again and again. The accuracy at which children learn new words is also amazing. Children as young as two or three years old is not taught words in terms of definition. They pick up meanings of words in context. For example, when I pick up a thick, black pen and tell them it is called a "pen," children almost always understand what I mean by a "pen." They rarely, if ever, make the mistake of thinking that what I meant by "pen" was in reference to its being black, or thick. This suggest that there must be some kind of intuitive system of "rules" regarding language.
Like other neural functions, the ability to learn language has a critical period (though this critical period may be longer compared to others). Many theoretical works have demonstrated that an "important regression of connectivity (and even of cell number) takes place as learning progresses" (Danchin 33). The brain goes through "pruning" of unnecessary connections as language development takes place. In other words, the neuronal synaptic connections are not created, or built, as we learn language: they pre-exist: unnecessary ones merely decay as language learning takes place. Such processes occur in the formation of synapses in sensory systems. For example, in development of visual system, synaptic formation is ruled by the "fire together, wire together" principle. Early in the developmental stage, the visual system receives overwhelming amount of input and there is a high branching of synaptic connections. As some inputs become more dominant (either in number or intensity) certain synaptic connections are reinforced and other connections that are less frequently utilized decay and disappear. No one denies the existence of strict biological constraints that govern sensory modalities. If the neurological development in language acquisition is parallel to the development of sensory modality, it would be a strong evidence against the constructivist model which insists that language is built through interaction with the environment.
Deaf parents have a non-oral ‘linguistic?interaction with their children much earlier than normal parents. Serazin has made observation that the neurological development of children born from deaf parents was more normal than the development of deaf children born to normal parents (Danchin 33). Such examples suggest that although the individual performance is the result of interaction with the environment, the fundamental rules of syntax are imposed by the neuronal structure.
Another fact that supports the critical period of language acquisition and thus the selectivist model is that the ability to learn language fluently.