Symbols and structures in language acquisition

Carolyn Johnson, Henry Davis, and Marlys Macken

The phonological (sound) system of a language is rule-based. Very young human infants can discriminate the majority of the features which comprise the adult sound system, and can do so across complex physical dimensions. At a minimum, infants' abilities provide an initial grid for segmenting, sorting, and classifying phonetic categories, and for mapping these to the higher levels of phonological systems. For production, there is continuity from the babbling period into early language. The early productive sound systems appear to be based on words rather than smaller units, words not being initially analysed into their component phonemes. This analysis begins between the ages of two and four years, although the child's system still remains simplified compared to that of the adult. The process of phonological development follows no invariant sequence, and can show regressions at the same time as the system becomes more complex. Some form of 'cognitive' theory at present provides the best explanatory framework

Verbal communication is preceded by gestural communication, beginning at about nine months of age. Accounts have been offered in which gestural communication is claimed to be necessary for later language development, and continuous with it; but the evidence on both these points is equivocal. Meaningful 'words' are used from about one year of age. There is a spurt in vocabulary development from around eighteen months. Errors in word use provide the major data source for theories of semantic development. These data have formed the basis of a number of theoretical accounts; but none of these are yet comprehensive in their explanatory powers. Crucially lacking is an account of how the child learns to relate words to concepts, and clear criteria for determining when a child's 'words' are truly symbolic.

The acquisition of syntax can be divided into three stages: presyntactic; syntactic; and postsyntactic. Early presyntactic word-combinations are of three types: the combination of words that reflect grammatically relevant real-world relations; a word plus an intonationally integrated but meaningless extra syllable; and formulaic or rote-learned sequences. It is not clear whether there is any continuity between the combinatorial structures of this stage and those of the next, syntactic, stage, which lasts from about two to five years of age. First-language learners make very few errors in constructing complex grammars - a fact supporting the claim that there are innate constraints, whether specifically linguistic or not, on a learner's 'hypothesis space'. Analysis of errors in learning suggests that morphological learning may occur via a probabilistic mechanism, whereas syntactic learning may be based on different, possibly innate, principles. The final postsyntactic stage represents the integration of the newly-emerged syntactic system with the real-world knowledge the child has accumulated.

Early functions of language are of three types: solicitation of action, social interaction, and joint attention; expression of affect; and participation in games. With the advent of naming, children can also label and request labels. Later developments, such as threatening, promising, and deceiving, have not been systematically studied.