Language acquisition: research methods
Much language acquisition research is longitudinal. Three general approaches can be found:
· Theory-driven. The researcher adopts a theoretical framework; then seeks support for it in their data. This approach is particularly favoured by those who subscribe to Chomskyan theory, and who seek (for example) to trace evidence of infants setting parameters in the direction of the target language. The children might be asked to make grammaticality judgements, indicating whether they regard a sentence as grammatically acceptable or not.
· Observational, analysing the data without prior assumptions. Diary studies have proved informative – though their disadvantage is that they do not preserve a record of the actual speech event. Video and cassette recordings have been widely used. They are obtained during regular meetings between researcher and infant; or by use of a timer.
· Experimental. It is obviously difficult to engage very young subjects in experimental tasks. Two types of method have proved useful:
- the high amplitude sucking procedure. An infant’s sucking on a teat settles down to a regular rhythm if there is little in the environment to distract the child – but speeds up markedly if something novel engages its attention. This phenomenon can be used to establish the extent to which infants discriminate between similar linguistic features, a change of sucking rate showing that they have identified a sound or rhythm that differs from an earlier one.
- the operant headturn procedure, in which an infant is trained to turn its head when it encounters a novel stimulus. An independent observer notes when the infant moves its head through at least 30º, and this is taken to show that the infant has noticed a change in the signal. A variant is the Headturn Preference Procedure, where different stimuli are played from different sides (e.g. an utterance in the ambient language on the left followed by an utterance in another language on the right). The infant’s headturns are monitored as an indication of which stimuli it finds more interesting.
For older infants, ‘listen and repeat’ tasks have been used to investigate areas such as phonological memory and lexical segmentation. In addition, many experimenters (especially those researching morphology acquisition) have used simple picture-based tests. The researcher might, for example, show the infant a picture of an object and name it a wug; then show the infant a picture of two and ask for a response.
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Language acquisition researchers have the benefit of a rich archive in the Child Language Data Exchange System (CHILDES) database collected by Brian MacWhinney and Catherine Snow, which brings together data from nearly a hundred research projects in a variety of languages.
Language acquisition: stages
All infants pass through the same stages in the acquisition of a first language; but they progress at different rates. So, while a child’s age in years and months is often cited (as two figures separated by a semicolon), it is not a reliable indicator of development. Many accounts record development in terms of the phonological or linguistic content of the child’s productions. The following stages are universal, the first two being prelinguistic:
· Cooing (about 0;3). Gurgling moves on to vocalisation involving sounds which resemble vowels. The infant responds vocally to human speech.
· Babbling (from 0;6). The infant produces consonant-vowel (CV) sequences which may resemble those of the target language. The child’s later productions become imitative: there is often a phase of echolalia from about 0;8, when the child imitates adult intonation patterns with some degree of accuracy.
· One-word stage (from 1;0). Sometimes termed holophrastic speech. The first words appear at about 1;0, and by 1;6 the child may have a vocabulary of around 50 words, usually nouns. The child recognizes the referential function of words, using them to name objects.
· Two-word stage (1;6 onwards). Sometimes described as telegraphic speech because of the absence of most function words. The two-word combinations exhibit a set of primitive semantic relationships (constituting a child grammar) of which the earliest are usually naming (this), recurrence (more) and non-existence (no). At about the same time, the vocabulary spurt begins, with an increase of about six to ten words a day in the child’s repertoire.
· Multi-word stage (2;6 onwards). The child uses strings of three or more words, often based upon established two-word patterns. Adult syntactic patterns gradually become more prevalent.
Instead of age, a more precise way of calibrating the development of an infant is by mean length of utterance (MLU): a figure based on the average number of morphemes in the infant’s productions. This is said to be a reliable marker of development until the age of about 4;0.
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Using MLU, early researchers proposed six stages of development.
Table 1. Six stages of first language acquisition (Brown, 1973)
| Stage | MLU | Approx. age | Characteristics |
| I | 1.0–2.0 | 1;0–2;2 | Holophrastic speech |
| II | 2.0–2.5 | 2;3–2;6 | Telegraphic speech |
| III | 2.5–3.0 | 2;7–2;10 | Inflections added |
| IV | 3.0–3.75 | 2;11–3;4 | Full sentences |
| V | 3.75–4.5 | 3;5–3;10 | Embedded sentences |
| V+ | 4.5+ | 3;11+ | Co-ordination |
Those who take a Piagetian perspective have attempted to relate progress in language to the cognitive developments of the sensorimotor period (age 0–2) and the pre-operational period (2–7). These include object permanence, the formation of categories and an understanding of causality and displacement. The argument is that the child cannot understand linguistic forms representing such notions until the notions themselves have been acquired. Vygotsky’s developmental stages also provide a loose framework for language development. Vygotsky identified a first stage when thought and language (a child’s first words) are unrelated; a second stage of egocentric speech when the child expresses its thoughts aloud; and a third when egocentric speech becomes internalised.
Yet another account of the stages of acquisition represents them in terms of the pragmatic functions which the child commands rather than surface features of syntax.
In any of these accounts, some caution has to be exercised in accepting productions as evidence of development. Receptive recognition of form and understanding of meaning may occur well before an item appears in production. Conversely, the production of a form might predate ‘acquisition’: it might, for example, result from mimicry without understanding.
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