Language development in children with mental retardation
National Council of Educational Research and Training
According to DSM-IV mental retardation is characterized by significantly sub average intellectual functioning (an IQ of approximately 70 or below) with an onset before 18yrs of age, associated with significant deficit or impairment in adaptive functioning (a collection of skills the people learn to function effectively in their everyday life) .
Four degrees of severity of mental retardation can be specified, reflecting the level of intellectual impairment: Mild, Moderate, Severe and Profound.
Mild Mental Retardation: IQ Level 50-55 to approximately 70
Moderate Retardation : IQ Level 35-40 to 50-55
Severe Mental Retardation: IQ Level 20-25 to 35-40
Profound Mental Retardation: IQ Level below 20 or 25
A retarded person is generally limited at least to some extent in six adaptive skills needed for daily living-communication, social skills, academic skills, sensorimotor skills, self-help skills and vocational skills.
The present article deals with the communication (language aspect). Children with mental retardation are compared to normally developing children with regards to their language development.
Linguists have divided language into several major aspects. One division refers to whether the language is being received or expressed i.e., receptive or expressive language. Another division identifies language systems i.e., phonology, syntax, morphology, semantics and pragmatics.
Reception: when receiving language, one not only hears it, but also comprehends it. Similarly when one is reading, one is receiving language. Therefore, receptive language comprises of hearing and comprehending and reading and comprehending.
Expression: expressive language refers to the production of language. Usually, one expresses oneself by speaking and in writing. Therefore, expressive language comprises both written and spoken language.
Given below is the relationship among dimension of reception and expression and the language systems of phonology (sound system of language); syntax (rules used to put words together into sentences); morphology (the use of grammatical markers that indicate number, tense, gender etc); semantics (meaning of words and word combinations); pragmatics(the way in which language is used in social situations).
Receptive: hearing, discriminating of sounds in language.
Expressive: speaking, production of sounds of language.
Receptive: comprehending how structure of language or order of words affects meaning.
Expressive: producing language with structure that communicates meaning.
Receptive: comprehending meaning units
Expressive: producing meaning units.
Receptive: comprehending word meanings (vocabulary)
Expressive: producing language using words meaning (vocabulary)
Receptive: comprehending language in light of its social context.
Expressive: producing language suitable to the social context.
Newborns arrive prepared to acquire language. There is distinct preference for human speech over other sounds (Morse, 1972). Along with this, newborns interest in human faces (Bushnell, Sai, & Mullin, 1989) and their capacity to imitate facial expressions (Meltzoff & Moore, 1977) prepare then for the social basis of communicative development.
The following section discusses the early vocal delays in infants with retardation particularly Down syndrome. Next, different patterns of social interaction that have been identified in children with different kinds of retardation have been discussed.
During the first year of life infants develop the capacity to produce speech sounds. They proceed through stages of cooing (around 2 months) and babbling.
Babbling which starts in the second half of first year is an important precursor to the meaningful speech. Babies start to produce consonant-vowel syllables such as mama or dada.
Research on babbling in infants in Down syndrome as compared to normally developing infants by Oller and his colleagues showed that infants with mental retardation were about two months behind normally developing group (Lynch, Oller, Eilers, & Basinger, 1990; Steffens, Oller, Lynch & Urbano, 1992) and more over babbling was significantly less stable as compared to normally developing infants due to motor delays and hypotonicity that are characteristic of Down syndrome (Lynch et al., 1990).
The first year of life is rich in parent-child interactions which are reciprocal involving both vocalizations and eye-gaze coordination (Trevarthen, 1979). These patterns build upto intentional communication at the around the age of nine months moving from simple dyadic interactions (0-5 months, involving face-to-face exchanges of affective signals between the infant and the caregiver) to more complex triadic interactions (6-18 months, i.e., to coordinate the attention of self and another person vis-ŕ-vis some third object or event). The infant at this stage tries to communicate and interpret a variety of meanings through eye gaze patterns, vocalizations and gestures.
One example of triadic interaction is joint attention which involves the infant’s ability to coordinate gaze between a social partner and an object. Children often mark joint attention to their social partner by using a pointing gesture, in an effort to communicate their interest in the object or to comment on the object (Bruner, 1975). Joint attention is an example prodeclarative communication, defined as a comment or statement about object by touching it, holding it up or pointing to it (Bates, Camaioni, & Volterra, 1975). Infants also express protoimperative meanings, through vocal play and pointing, to request object or activities from their social partner. Finally, children use variety of gesture to mark social regulatory communicative acts, such as greetings.
These early social and communicative achievements are viewed as necessary prerequisites for different aspects of language acquisition (Bruner, 1975; Tomasello, 1992).
Infants with Down syndrome show delays in the onset of mutual eye contact (Berger & Cunninghan, 1981), they vocalize much less than other infants (Berger & Cunninghan, 1983) and their dyadic interactions with their mothers are less coordinated (Jasnow et al., 1988). By the second half of the first year they catch up. However, they fixate primarily on the eyes rather than exploring other facial features and they vocalize more than normal infants (Berger & Cunningham, 1981). This increased interest in people in the later part of the first year, through eye gaze is accompanied by a lower level of interest in objects and toys. Thus, Down syndrome one year olds show difficulty interacting with their mothers and playing with objects at the same time (Ruskin, Kasari, Mundy & Sigman, 1994).
These early differences in the social patterns of infants with Down syndrome are reflected in their play and intentional communication in the second year of life.
Mundy and his colleagues in a comprehensive study compared a large group of toddlers with Down syndrome to mental-age-matched subjects with non specific retardation and normally developing children on the Early Social Communication Scales (Mundy, Sigman, Kasari & Yirmiya, 1988). They found that the subject with Down syndrome showed right frequencies of social interaction behaviours, similar to the findings of infants studies, but lower frequencies of object request behaviors or protoimperatives.
Thus, it is seen that Down syndrome children focus more on people and less on objects which further related to low frequencies of object requests, which may by further reflected in over all expressive language delays.
Prelinguistic development in other retarded population such as fragile X syndrome has known to show poor eye contact. Whereas, young children with Williams syndrome are extremely interested in human faces and spend extended period of times looking intently at another person’s face (Bellugi, Bihrle, Neville, Jernigan & Doherty, 1992).
Thus, the above given studies allow us to explore the relationships between prelinguistic development and later language acquisition. Clearly, more work needs to be done on the early social-communicative development of children with different forms of mental retardation.
Semantics is concerned with understanding the meaning of words and words in groups, particularly sentences.
At about one year of age, the child utters his or her first words, thereafter, language acquisition occur exceedingly rapidly. There is vocabulary spurt, when the number of different words children says suddenly increases, also referred to as naming explosion. By the time children are about 30 months old, they are able to produce over 500 words and comprehend even more (Fenson et al., 1994) as in comprehension children only need to recognize the meaning of the word, whereas in production they have to recall or retrieve from their memories the word as well as the concept for which is stands (Kuczaj, 1986).
Regarding vocabulary growth in children with Down syndrome, some develop vocabularies at the rate that is comparable to their mental-age level, whereas others may be significantly delayed because of their articulatory deficits (Miller, Sedley, Miolio, Murray-Branch & Rosin, 1992). Whereas, children with Williams syndrome have shown rapid rates of vocabulary growth that may even surpass their mental ages (Mervis & Bertrand, 1997; Singer, Bellugi, Bates, Jones, & Rossen, 1994).
To understand how young children acquire such a large vocabulary so rapidly and effortlessly, the role of operating principles have been emphasized. These principles limit the set of possibilities that children must consider when they hear a new word. These usually develop as the child gains experience with words in the process interacting with their care givers.
Recent research on lexical development in children with Down syndrome has focused on the use of operating principles in acquiring new words (mostly object labels). Normally developing use words to label objects at the so-called basic level (e.g., car, dog) rather than more specific subordinate (e.g., Mercedes, Terrier) or more general super-ordinate (e.g., vehicle, animal) levels. Objects too are sorted at the basic level such as children tend to place all cars together in one group, all dogs in another group and so forth (Mervis & Rosch, 1981).
Mervis & his colleagues (Cardoso-Martins, Mervis & Mervis, 1985; Mervis, 1988,1990) found that retarded children are also sensitive to the salience of the basic level in their object categorization and early word learning. Even older children with Down syndrome and retardation of unknown origin have better comprehension of words at basic level as compared to subordinate or super-ordinate levels (Tager-Flushberg, 1985a).
Similar results have been found for very young children with Williams syndrome (Mervis & Bertrand, 1997).
Other operating principle that has been found to play a very important role is the principle of extendibility. For example, a child might use the word car to refer to many objects including buses, trains, trucks etc.
Again studies by Mervis and her colleagues have confirmed that children with Down syndrome and Williams syndrome extend the meaning of words in the similar way like normal children (Cardoso-Martins et al., 1985; Mervis, 1988, 1990; Mervis & Bertrand, 1997).
Another lexical principle that has been investigated is called the whole object constraint (Macnamara, 1982; Markman & Wachtel, 1988) which states that words refer to whole objects rather than its parts or attributes and the novel name-nameless category principle that plays a very important role in children’s rapid word learning abilities, especially the capacity to map meaning of new words. e.g., in a group of mostly familiar item with one novel item and a novel word, a child will quickly associate the new word with the novel item.(Golinkoff et al., 1994). After the appearance of this principle word learning becomes very rapid and much less effortful.
Studies by Mervis and Bertrand (1997) have shown that both Down syndrome and Williams syndrome children learn words for whole object rather than about attributes or parts of any objects. These children also acquire the novel name-nameless category principle at about the same time they are able to sort.
Thus, it can be concluded from the above discussion that different forms of retardation follow the same set of universal principles in acquisition of word meanings (however, this may not be true for severely and profoundly impaired children).
As children acquire the meaning of words, they are also learning how to articulate these words following the phonological rules of the language. Most of the phonological development is complete by the time children go to school. However, they continue to make certain articulation errors that reduce or simplify their language (Ingram, 1986).
Children with retardation, particularly those with lower IQ, tend to exhibit articulation deficits (Abbeduto & Rosenberg, 1993).
Children with Down syndrome exhibit difficulties with the phonological aspects of language which can be related to their delayed onset in babbling & which further explains their overall delays in expressive language.
Dodd (1976) compared phonological errors made by severely retarded children with Down syndrome, by children with non specific retardation, and by normally developing children, matched on overall cognitive mental age. Children with Down syndrome produced more errors and more different types of errors than either of the two groups and their phonological development lagged significantly behind their cognitive level.
A study by Stoel-Gammon (1980) on spontaneous speech produced by a group of mildly retarded children found that her subjects were capable of producing all the phonemes of English suggesting no evidence for deviance in this area of language. Moreover, it was found that the phonological abilities of children with Down syndrome were comparable to those of normally developing children at the same language level and like Dodd (1976) her subjects were clearly delayed relative to their cognitive mental-age levels.
In contrast children with Williams syndrome did not appear to have particular problems with articulation. Gosch, Stading & Pankau (1994) on a large sample of children with Williams syndrome found that their articulation was significantly better than a mental age-matched group of children with non-specific retardation.
Various clinically studies of older boys with fragile X syndrome have shown that this population has problems both with articulation and fluency of speech production (Dykens, Hodapp & Leckman, 1994).
Since, these difficulties with speech production are not related to mental age or IQ, Dykens et al. (1994) hypothesized that may be linked to attentional and sequencing that are characteristic of this population.
Thus, it can be concluded there are broad similarities in the kinds of developmental error patterns that are made by children across these groups and those in normally developing children. This highlights the universal aspects of speech articulation processes.
After naming explosion, children usually begin to combine words to create simple two word utterances, also called telegraphic speech. Gradually, children’s sentences increase in length as they add more semantic and grammatical elements. This growth is measured in terms of child’s mean length of utterances (MLU; Brown, 1973).
At the early stages of language development, open class categories dominate the child’s vocabulary (nouns, verbs, adjectives, adverbs) but as MLU grows, children use increasing closed-class terms such as pronouns, prepositions, conjunctions.
Early stages of grammatical development in retarded population are similar to that found in normally developing children.
Various studies on young children with Down syndrome have found widely varying rates of change in MLU within this population (Beeghly, Weiss-Perry & Cicchetti, 1990; Fowler, Gelman et al. (1994).
For example, Fowler et al. (1994) studied a young girl with Down syndrome who did not begin to create two word utterances until about the age of 4. However, her rate of development after this point was rapid and did not differ from normal until she reached MLU of 3.5 when she was five-and-a-half years old.
Tager-Flushberg et al. (1990) found rapid rates of development during the early stages of syntactic growth for two out of six children with Down syndrome. Other children with Down syndrome who had IQ scores below 50 (Fowler, 1988) did not begin combining words until the age of five or six. They then spend a long period in which they use relatively few two word utterances. Thus, their rate of development is very slow and these children never develop beyond the early stages of grammatically development (Dooley, 1976; Miller, 1988).
Furthermore, Singer et al., 1994 found that children with Down syndrome use simpler and shorter sentences as compared to normal children and children with Williams syndrome. Most of the children with Down syndrome fail to acquire complex grammatical constructions such as correct use of complex questions.
In contrast children with Williams syndrome are able to acquire adult-level grammatical system and do not show specific syntactic deficits (Bellugi et al., 1992; Tager-Flushberg et al., 1990).
Bates and her colleagues demonstrated that lexical and grammatical development are joined at the early stages (Bates, Bretherton, & Synder, 1988). Initially, children’s vocabularies are composed of or noun like words to label things in the environment. Once it reaches a critical size, children begin to combine words. At this point there is increase in closed class terms such as pronouns, demonstratives, conjunctions and so forth. There are individual differences at these early stages, with some children using fewer nominals and more of pronouns and demonstratives (expressive or pronominal children) and some who use relatively more of nouns (referential children).
Various studies of children with Down syndrome have indicated that majority of population fits the pronominal profile. These children tend to rely heavily on pronouns and demonstratives (e.g., referring to objects and people as it, this or he) and use fewer nominal terms during the early stages of language development (e.g., Dooley, 1976; Singer et al., 1994; Tager-Flusshberg et al., 1990). This reliance on pronouns and demonstrative rather than specific noun can be due to memory limitations, word-finding difficulties, or both.
From the above discussion it can be concluded that retarded children acquire syntactic and morphological knowledge in the same way and in the same order as the normally developing children. However, beyond the early stages clear differences begin to emerge with some children in particular populations. For example, children with Williams syndrome acquire mature grammatical system, whereas children with Down syndrome show serious limitations in the grammatical development. This deficit in children with Down syndrome may be due to specific impairment to the mechanism that serves to process linguistic information (Fowler, 1990).
Besides phonology, vocabulary and grammar, children must learn to use language effectively in social contexts. In a normal conversation participants should be able to take turns, stay on the same topic, state their messages clearly and confirm to cultural rules that govern how individuals are supposed to interact.
Studies of normally developing children have investigated several aspects of pragmatic development, including the development of speech acts, conversational competence and sensitivity to the listeners needs. We perform speech acts when we request, command, complain, refuse, interact etc.; conversational competence i.e., being able to maintain a topic of conversation for a longer time, engaging in appropriate turn taking behaviour and being able to add new information to the ongoing topic; sensitivity to the listeners needs by responding appropriately to requests for clarifications.
In contrast to syntactic delays and deficits in children with Down syndrome, pragmatic abilities are an area of relative strength. A cross-sectional study by Coggins, Carpenter and Owings, 1983 compared a group of four children with Down syndrome, whose MLUs ranged from 1.7 to 2.0 to an MLU matched group of four normally developing children. Overall the findings indicated that the children with Down syndrome expressed the same range of communicative intents or speech acts as compared to the normally developing children. However, potential differences were found between speech acts that involve instrumental functions (mainly requests; e.g., want water, cookie) and those involving interpersonal functions (e.g., see this).
It was found that children with Down syndrome involve less in requesting behaviours as compared to the normal group. However, the frequencies of comments, answers and protests wee more or less equivalent.
Beeghly et al (1990) in a lager study of children with Down syndrome compared them to a group of young MLU matched normal children and a group of slightly older mental age matched normally developing children. It was found that children with Down syndrome engaged less in requesting behaviour than the mental-age matched normally developing children (similar to Coggins study) but they were more comparable in their requesting behaviour to the language matched group.
The limited use of requests by children will Down syndrome could be viewed as related to their lower arousal and passivity (Beeghly et al., 1990).
In normally developing children various studies have shown that the ability to take turns in conversations does not show any developmental change with increasing language abilities (Bloom et al., 1976). From the beginning children know that they should respond verbally to their mothers’ utterances. Furthermore, their conversation becomes more advanced with increases in their linguistic capacity. They are able to maintain a topic of conversation over increasing number of turns (Bloom et al., 1976).
Beeghly et al. (1990) found that children with Down syndrome are good at maintaining a topic of conversation for a longer period, can engage in appropriate turn taking behaviour as compared to the language-matched controls, suggesting this aspect of language as an area of relative strength.
Young children with Williams syndrome were also good at maintaining the ongoing topic in interaction with an adult examiner (Kelley and Tager-Flushberg, 1994).
According to several descriptive studies, males with fragile X syndrome have difficulties in maintaining a conversational topic. They tend to perseverate more than other subjects with nonspecific retardation, and also use considerable amount of inappropriate language (Ferrier, Bashir, Meryash, Johnston, & Wolff, 1991).
From the early stages of language development, young normal children begin to demonstrate sensitivity to their conservational partner. Even a two-year-old may repeat an utterance or change the form of an utterance if their partner does not respond (Foster, 1990). Similarly, children with Down syndrome will revise, rather than repeat if a listener requests clarification of a pervious aspect of the message. Children with Williams syndrome are also good at conversational repairs (Kelley & Tager-Flushberg, 1994).
The ability to express and modify language according to one’s listeners background, social role, level of understanding and so forth, continues to develop during early school years that complex integration of social, cognitive and linguistic achievements. At these advanced levels children with retardation face difficulties that go beyond their cognitive and linguistic levels (Abbeduto & Rosenberg, 1993).
Thus, it can be concluded that though children with intellectual disabilities do acquire basic pragmatic language skill, more subtle aspects of conversational competence is less commonly displayed.
The overall picture of early language development in children with retardation provides strong evidence for differences and similarities as well as various delays in comparison to normal children.
It is seen that retarded children follow same set of universal principles in acquisition of word meaning (not true for severely and profoundly retarded children). Similarly, there are broad similarities in the kinds of phonological errors made by these children and those in normally developing children suggesting the universal aspects of speech articulation process.
Furthermore, it is seen that retarded children acquire syntactic and morphological knowledge in the same order as the normally developing children (in the early stages).
With regards to pragmatic skills children with intellectual disabilities to acquire basic pragmatic skills, however, more subtle aspects of conversational competence are less commonly displayed.
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