Language Disorders Health Article

Language disorders and mental retardation

Mental retardation can also affect the age at which children learn to talk. A mentally retarded child is defined as one who falls in the lower end of the range of intelligence, usually with an IQ (intelligence quotient) below 80 on some standardized IQ tests. There are many causes of mental retardation, including identified genetic syndromes such as Down syndrome, Williams syndrome, or fragile X syndrome.

Retardation can also be caused by damage to the fetus during pregnancy due to alcohol, drug abuse or toxicity, and disorders of the developing nervous system such as hydrocephalus. Finally, there are environmental causes following birth such as lead poisoning, anoxia, or meningitis.

Any of these situations is likely to slow down the child's rate of development in general, and thus to have effects on language development. However, most children with very low IQs develop some language, suggesting it is a relatively "buffered" system that can survive a good deal of insult to the developing brain. In cases of hydrocephalus, for example, it has been noted that children who are otherwise quite impaired intellectually can have impressive conversational language skills. Sometimes called the "chatterbox syndrome," this linguistic sophistication belies their poor ability to deal with the world. In an extreme case, a young man with a tested IQ in the retarded range has an apparent gift for acquiring foreign languages, and could learn a new one with very little exposure. For example, he could do fair translations at a rapid pace from written languages as diverse as Danish, Dutch, Hindi, Polish, French, Spanish, and Greek. He is, in fact, a savant in the area of language, and delights in comparing linguistic systems, although he does not have the mental capacity to live independently.

Adults should not consider retarded children to be a uniform class; different patterns can arise with different syndromes. For example, in hydrocephalic children and Williams syndrome, language skills may be preserved to a degree greater than their general intellectual level. In other groups, including Down syndrome, there may be more delay in language than in other mental abilities.

Most retarded children babble during the first year and develop their first words within a normal time span, but are then slow to develop sentences or a varied vocabulary. Vocabulary size is one of the primary components of standardized tests of verbal intelligence, and it grows slowly in retarded children. Nevertheless, the process of vocabulary development seems quite similar: retarded children also learn words from context and by incidental learning, not just by direct instruction.

Grammatical development, though slow, comes in the same way, and in the same order, as it does for normal IQ children. The child's conversation, however, may contain more repetition. The Down syndrome adolescent with an IQ of around 50 points does not seem to progress beyond the grammatical level of the normally intelligent child at three years, with short sentences that are restricted in variety and complexity. Children with Down syndrome are also particularly delayed in speech development. This is due in part to the facial abnormalities that characterize this syndrome, including a relatively large tongue. It is also linked to the higher risk they appear to suffer from ear infections and hearing loss.

Specific language impairment

Specific language impairment describes a condition of markedly delayed language development in the absence of any apparent handicapping conditions such as deafness, autism, or mental retardation. Specific language impairment (SLI) is also sometimes called childhood dysphasia, or developmental language disorder.

Children with SLI usually begin to talk at approximately the same age as normal children, but are markedly slower in their progress. They seem to have particular problems with inflection and word forms, such as leaving off endings when forming verb tenses (for example, the -ed ending when forming the past tense). This problem can persist much longer than early childhood, often into grade school and beyond, where these children encounter difficulties in reading and writing. The child with SLI often has difficulties learning language "incidentally," (picking up the meaning of a new word from context or generalizing a new syntactic form). This is in contrast to the normal child's development, where incidental learning and generalization are the hallmarks of language acquisition. Children with SLI are not cognitively impaired and are not withdrawn or socially aloof like the autistic child.

Very little is known about the cause or origin of specific language impairment, although evidence is growing that the underlying condition may be a form of brain abnormality. However, any such brain abnormality is not readily apparent with existing diagnostic technologies. When compared to other children, SLI children do not have clear brain lesions or marked anatomical differences in either brain hemisphere.