Speech perception

Another important area of psycholinguistic research that has been strongly influenced by theoretical advances in linguistics and, more especially, by the development of generative grammar is speech perception. It has long been realized that the identification of speech sounds and of the word forms composed of them depends upon the context in which they occur and upon the hearer’s having mastered, usually as a child, the appropriate phonological and grammatical system. Throughout the 1950s, work on speech perception was dominated (as was psycholinguistics in general) by information theory, according to which the occurrence of each sound in a word and each word in an utterance is statistically determined by the preceding sounds and words. Information theory is no longer as generally accepted as it was a few years ago, and more research has shown that in speech perception the cues provided by the acoustic input are interpreted, unconsciously and very rapidly, with reference not only to the phonological structure of the language but also to the more abstract levels of grammatical organization.

Other areas of research

Other areas of psycholinguistics that should be briefly mentioned are the study of aphasia and neurolinguistics. The term aphasia is used to refer to various kinds of language disorders; research has sought to relate these, on the one hand, to particular kinds of brain injury and, on the other, to psychological theories of the storage and processing of different kinds of linguistic information. One linguist has put forward the theory that the most basic distinctions in language are those that are acquired first by children and are subsequently most resistant to disruption and loss in aphasia. This, though not disproved, is still regarded as controversial. Two kinds of aphasia are commonly distinguished. In motor aphasia the patient manifests difficulty in the articulation of speech or in writing and may produce utterances with a simplified grammatical structure, but his comprehension is not affected. In sensory aphasia the patient’s fluency may be unaffected, but his comprehension will be impaired and his utterances will often be incoherent.

Neurolinguistics should perhaps be regarded as an independent field of research rather than as part of psycholinguistics. In 1864 it was shown that motor aphasia is produced by lesions in the third frontal convolution of the left hemisphere of the brain. Shortly after the connection had been established between motor aphasia and damage to this area (known as Broca’s area), the source of sensory aphasia was localized in lesions of the posterior part of the left temporal lobe. Subsequent work has confirmed these findings. The technique of electrically stimulating the cortex in conscious patients has enabled brain surgeons to induce temporary aphasia and so to identify a “speech area” in the brain. It is no longer generally believed that there are highly specialized “centres” within the speech area, each with its own particular function; but the existence of such a speech area in the dominant hemisphere of the brain (which for most people is the left hemisphere) seems to be well established. The posterior part of this area is involved more in the comprehension of speech and the construction of grammatically and semantically coherent utterances, and the anterior part is concerned with the articulation of speech and with writing. Little is yet known about the operation of the neurological mechanisms underlying the storage and processing of language.