Learning to Speak
Chomsky and the Poverty of the Stimulus
Chomsky demonstrated that children acquire linguistic rules or grammar without an inexhaustive sample of the acquired language. In other words, children cannot learn the rules of grammar by mere exposure to a language (Chomsky, 1965). For one thing, children hear an imperfect input. Adult speech is full of slips-of-the-tongue, false starts and errors. Sometimes there are contractions such as gonna and wanna and words are not necessarily separated in continuous speech. There is also a lack of examples of all the grammatical structures in a language for children to derive all linguistic rules from analysing the input. All of these phenomena are often labelled the “poverty of the stimulus” (Berwick, Pietroski, Yankama, & Chomsky, 2011). Poverty of the stimulus is often used as an argument for universal grammar. This is the claim that all languages have some underlying common structure within which all surface structures of language emerge.
Language development is perhaps one of the greatest mysteries in psycholinguistics. The rapidity of first language acquisition is astounding to anyone who has tried to learn a second language as an adult. This process can be broadly divided into stages based on the characteristics of the infants’ output. However, we must note that output doesn’t always assure us a clear picture of the cognitive processes that are going on within the infants’ minds.
As seen in Figure 5.1, infants make vegetative sounds from birth. These include crying, sucking noises and burps. At around 6 weeks, we start getting cooing sounds followed by vocal play between 16 weeks and 6 months (Stark, 1986). This vocal play involves sounds that appear similar to speech but containing no meaning. Babbling is observed between 6 to 9 months. This is different from vocal play in that it contains true syllables (generally CV syllables as in ‘wa wa’ for ‘water’). Children produce single-word utterances around 10 to 11 months followed by an extraordinary expansion of vocabulary around 18 months. At the same time, we start to get two-word utterances. We also start to get telegraphic speech. These are utterances which lack grammatical elements (Brown & Bellugi, 1964). Grammatically complex utterances emerge around two and a half years.
Figure 5.1 Language Acquisition Milestones
Research methods that we can employ with adults is not always possible with infants. One technique is the sucking habituation paradigm. This paradigm measures the rate of sucking an artificial pacifier as a measure of interest by the infant in a novel stimulus. It has been observed that babies prefer novel stimuli as opposed to stimuli that are familiar. If they are presented with habituated (or familiar) stimuli and then a novel stimulus pops up, the rate of sucking increases. This can be used to see whether an infant can detect the difference between who stimuli. Another technique is the preferential looking technique. Here children look longer at scene that are consistent with what they are hearing. Using such techniques (and others), psycholinguists try to determine at what age children understand the difference between phonemes, morphemes and understand syntax.
The simplest form of language acquisition would be simple imitation of adult language. While children do imitate adult behaviour to some extent, this alone cannot account for language development. The sentences produced by children acquiring language do not show imitation of adults. Children often make errors that adults don’t make. However, imitation may play a role in the acquisition of accents, speech mannerisms and specialized vocabulary.
Skinner (1957) argued that language acquisition happens through the same mechanisms of operant conditioning that operated on other human and animal behaviour. However, adults generally do not encourage children to speak like them. On the contrary, adults often imitate the childish speech of children when speaking to them. If any correction is made, it is regarding the accuracy of the statements rather than their syntax.
Another observation that learning theories cannot predict is the pattern of acquisition of irregular verb and noun forms. Saying *gived instead of gave or *gooses instead of geese are some examples of this. Children generally show a pattern of correct imitation of the stem but then incorrect production. These incorrect productions are usually because of over-regularization of the past tense or plural forms of the stems. Finally, children produce the correct forms. This is an example of U-shaped development: performance starting off well, then deteriorating before improving. In essence, language acquisition appears to be based on learning rules rather than learning associations.
The Language Acquisition Device
Chomsky (1965) argued for the existence of a language acquisition device (LAD). This is hypothesized to be an innate structure separate from intellectual ability or cognition. If the poverty of the stimulus is true, then children need something in additional to language exposure to arrive at language competency. The language acquisition device was later replaced by the concept of universal grammar. According to this idea, the child has innate rules of inference that enable them to learn a language. This would be a set of parameters that constrain and guide language acquisition. As languages vary in terms of their grammar, syntax and morphology, Chomsky hypothesized that language learning was essentially setting parameters using input from exposure to a language that in turn set other parameters automatically. In other words, languages cannot vary in any way possible with infinite variety. There are basic parameters that influence each other.
We can look at some examples of parameter setting across language. For example, if a language has subject-verb-object (SVO) word order, then question words (what, where, who, how) would come at the beginning of the sentence while a language that is subject-object-verb (SOV) would put them at the end.
- English (SVO): “What is your name?”
- Tamil (SOV): “உங்கள் பெயர் என்ன?” Your name what?
Some universals may be an innate part of grammar. For example, there is not obvious rationale for having all SVO languages putting question words at the beginning of their sentences. It is also possible that the external environment in which we evolved may play a role in the development of universals. Languages often note a difference between animate and inanimate object of sentient and non-sentient beings. However, there is some criticism about the idea that true universals, common to all languages, might exist.