DISORDER
In psycholinguistics, a divergence from the normal processes of speech and comprehension which is due to cognitive or affective factors. Elsewhere, the term also covers problems of speech production and reception which are physiological in origin.
Language disorders can be categorised in the following ways:
Acquired vs developmental. An acquired disorder is an impairment which occurs after a first language has been fully established. It may derive from brain damage (particularly to the left hemisphere) caused by illness, accident or surgery. It can also be part of general cognitive deterioration as the result of dementia.
A developmental disorder is an impairment which manifests itself during the acquisition of a first language. It might derive from processing problems, as with dyslexia and dysgraphia; or it might have affective causes, as in cases of stammering. The term also covers the effects upon language of the learning difficulties associated with autism, Down’s Syndrome or Williams Syndrome; and cases of delayed language acquisition known as specific language impairment (SLI). In principle, a developmental disorder has three possible effects: it can delay the normal process of language acquisition, it can change the order in which elements are acquired or it can result in language which deviates from what has been observed in studies of normal development. A major issue for researchers has been the attempt to establish whether a disorder results in delay or deviance.
The distinction between acquired and developmental disorders is sometimes marked by the use of different terms: the prefix dys- (= impaired) indicates a developmental condition and the prefix a- (= without) an acquired one. Thus, aphasia = acquired dysphasia; alexia = acquired dyslexia; agraphia = acquired dysgraphia.
Organic vs functional. In an organic disorder, there is a clear neurological or physiological cause. In a functional one, there are problems of psychological processing.
Reception vs production. Language disorders affect reception, production or both. With aphasia in particular, the condition may be mainly restricted to receptive aphasia or to expressive aphasia.
Performance vs system. In productive disorders, a distinction is sometimes made between speech disorders affecting phonology and language disorders involving the lexicon and the system of syntax. However, a more appropriate distinction is between disorders which affect performance at phonetic and graphetic level and disorders which affect the underlying system (phonological, graphological, semantic or syntactic).
The major topics of research fall into three areas:
Problems of fluency. For some speakers, these problems are largely psychological, as in cases of stuttering. Other speakers have difficulty because of physiological problems involving malformation or mis operation of the articulators (mouth, tongue, jaws, palate etc.). Cases such as these might appear to lie outside the scope of psycholinguistics; however, they raise questions about the nature of language and of language acquisition. Provided hearing and intelligence are not affected, it seems that the inability to speak does not prevent the development of language comprehension and inner speech.
Problems of written language. A distinction is made between dyslexia (reading difficulty) and dysgraphia (writing difficulty), though many subjects manifest both. The degree of impairment varies between individuals, as do specific symptoms. Some dyslexics appear to suffer from a phonological deficit– they have problems in guessing the spellings of non-words. Others show signs of a ‘whole word’ deficit and cannot recall the spellings of unusual words.
The relationship between language and cognition. Most human beings grow up to achieve full competence in their native tongue, regardless of wide variations in their intelligence and environment. This has suggested to some commentators that language develops independently of general cognition. Some of the evidence from language acquired in ‘special circumstances’ appears to contradict this hypothesis, while some appears to support it. Thus, studies of Down’s Syndrome and autism seem to demonstrate links between cognitive development and language. However, the reverse is suggested by evidence from two other conditions, specific language impairment and Williams Syndrome.
One difficulty in researching language disorders, both develop mental and acquired, is the extent to which they vary from one sufferer to another. It has been suggested that some disorders may not be unitary conditions, but may represent combinations of impairments which are present to different degrees in different sufferers.
See also: Ageing, Aphasia, Autism, Cluttering, Dementia, Down’s Syndrome, Dysgraphia, Dyslexia, Savant, Specific language impairment, Stuttering, Williams Syndrome
Further reading: Bishop (1997); Chiat (2000); Crystal and Varley (1999); Harris and Coltheart (1986)
