Language development in children with mental retardation
Gauri Pruthi
National
Council of Educational Research and Training
Abstract
The acquisition of language is one of the most remarkable achievements. Within few years children make the transition from cooing and babbling to becoming fully communicative individuals. Generally, children acquire the essential components of language by the age of three or four. However, this may not be true for children with mental retardation. There are various kinds of delays as compared to normal children and there are different patterns of language acquisition in different populations of children with mental retardation which are presented in this paper.
Mental
Retardation
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).
1)
Phonology-
Receptive: hearing, discriminating of
sounds in language.
Expressive:
speaking, production of sounds of language.
2)
Syntax-
Receptive:
comprehending how structure of language or order of words affects meaning.
Expressive:
producing language with structure that communicates meaning.
3)
Morphology-
Receptive: comprehending
meaning units
Expressive:
producing meaning units.
4)
Semantics-
Receptive:
comprehending word meanings (vocabulary)
Expressive:
producing language using words meaning (vocabulary)
5)
Pragmatics-
Receptive:
comprehending language in light of its social context.
Expressive:
producing language suitable to the social context.
Prelinguistic
Development
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.
Vocal
Development
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).
Social-Communicative
Development
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.
Semantic
Development
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).
Phonological Development
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.
Early Grammar
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.
Conclusion
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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