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Children's language disorders Recent research advances.

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CURRENT REVIEW
Chddren’s Language Disorders:
Recent Research Advances
Christy L. Ludlow, PhD
Between 3 and 8% of preschool children in Britain and the United States are delayed in their language development by more than a year below the normal range. Evidence suggests that such children are particularly impaired
in acquiring syntactic and morphological rules, although well-defined syndromes of impaired language development have not yet been determined. The effects of preschool impairments in language development on subsequent
school achievement are significant: 60% of these children are in special classes for the learning impaired at 9 years
of age. Auditory processing deficits have been demonstrated in language-impaired children, but the contributions
of such deficits to language development difficulties have yet to be determined. While autistic children have severe
cognitive disorders and visual and auditory perceptual disturbances, the difficulties of nonautistic languageimpaired children seem confined more to language expression and comprehension. Recent neuropsychological evidence concerning brain organization for language behavior suggests that these children have deficiencies in language functions which normally depend on left hemisphere functioning.
Ludlow CL: Children’s language disorders: recent research advances. Ann Neurol 7:497-507, 1980
This review discusses recent research and major
controversies concerning language disorders in children in order to interest investigators from various
specialities in this field and to inform practitioners of
its recent advances.
Definition of Children’s Language Disorders
Developmental language disorders may be primary
(and specific) or secondary. A primary disorder exists
when no other sensory or cognitive impairment is
present to account for the delay in language development. Secondary disorders include language disorders of the congenitally deaf and the severely
mentally retarded. Primary or specific language disorders involve both language comprehension and expression to varying degrees and are first noticed
when a child fails to speak by 2 years of age.
Language is a system of symbolic representation
used by human beings to communicate information.
Speech is the planning and execution of oral
movements required for speech articulation, the
channel used most frequently for language expression; writing and finger spelling are considered other
modes of language expression. Children who have
specific disorders of language development make
mistakes in their use and understanding of words and
may or may not have speech articulation errors as
well. When speech is unintelligible, the extent of the
speech articulation disorder and the language disorFrom the National Institute of Neurological and Communicative
Disorders and Stroke, National Institutes of Health, Bethesda,
MD.
der is often difficult to determine. Standardized tests
of language comprehension can contribute to the assessment of a child’s level of language development
independent of speech articulation.
Glossary of Terms
Affricate: A consonant produced by first blocking
airflow as for a stop and then slowly releasing the
airflow, causing turbulence as in a fricative sound;
for example, Ichl as in cheese.
Lexicon: The words contained in a language and
their semantic definitions.
Morpheme: The smallest meaningful unit of language, which occurs either as a word or within a
word. For example, troubleshooting contains three
morphemes, trouble-, -shoot-, and -ing. The acceptable use of words depends upon the morphemes
they contain. Morphemes may be words or be appended to words; for example: verb endings, -ed,
-ing; noun modifiers, -es, -s; adverb endings, -ly;
and adjective modifiers, -er, -est.
Morphology: The morphemes contained in a language and the system of rules followed by speakers
when combining morphemes in phrases.
Palatal fricative: A consonant made by partially
blocking airflow between the palate and tongue,
causing air turbulence and resulting in a sound; for
example, Ishl as in shoe.
Phoneme: A distinct sound unit recognized by
Received Aug 16, 1979, and in revised form N o v 5. Accepted for
publication Nov 11, 1979.
Address reprint requests to Dr Ludlow, NINCDS, Federal Bldg,
Room 1C-13, 7550 Wisconsin Ave, Bethesda, MD 20205.
497
speakers of a language. There are 46 phonemes in
English: 9 vowels and 37 consonants.
Phonology: The speech sounds of a language and
the rules followed by speakers when combining
and pronouncing speech sounds.
Semantics: The meanings in words and phrases. For
example, in English it would be unacceptable to say
“bachelor’s wife” since the two words are contradictory in meaning. Further, the sentence “The
baseball bat bit the girl” is unacceptable since a
baseball bat is not an animate object.
Syntactic structure: Descriptions of the structural
relationships between words in a sentence-the
representations of the grammatical pattern of a
sentence; for example, “The man is going to the
store” consists of Noun Phrase Aux Verb-ing
Prep + Noun Phrase.
Syntactic transformations: Rules which serve as
definitions of the structures of different sentence
types in a language. These rules describe the relationships between words, the overall form of
sentences, and how simple sentences are changed
from one type to another, such as questions, commands, passives, and embedded sentences. For
example, transformations of the sentence “You are
holding the boy up” are: question, “Are you holding the boy up?’’; command, “Hold the boy up”;
passive, “The boy is being held up by you”; and
embedded sentence, “I can see that you are holding the boy up.”
Unacceptable grammaticality: Syntactic structures
or sentences which are recognized by native
speakers of the language as not being well formed.
Such sentences do not follow the rules for forming
syntactic structures in a language.
Verb phrase: The part of a sentence which contains
the verb (the predicate) as well as all words,
clauses, and sentences modifying the verb. The
verb phrase is in italic in each of the following
sentences: “The man won’t go to the store today”;
“The girl should see the man going to the store”; and
“They had been dancing every dance when the club
+
+
+
closed. ’’
Voiceless bilabial (stop): A consonant made by
occluding airflow completely at the lips, letting
pressure build up, then releasing it in a sudden
burst. The only voiceless bilabial stop in English
is [pi.
Statement of the Problem
Language disorders are common. At 3 years of age,
3% of preschoolers in England were found to be language impaired to the extent of needing language
therapy before entering school [ 7 6 ] . A study in the
United States reported a much higher prevalence in
some segments of the population. Among white
middle class children between 3 and 4 years old in
498 Annals of Neurology Vol 7 No 6 June 1980
Detroit, 8.5% were a full year behind the normal
range on standardized language assessment batteries
[ 2 ] . Black dialect language assessment instruments
identified a much higher percentage of impairment
among black children. In both whites and blacks, the
prevalence of impairment was greater in lower than
in middle socioeconomic groups [ 2 ] . Wolpaw, Nation, and Aram [90] tested children at 9 years of age
who had been diagnosed as having primary language
impairment before they were 5 years old. Although
the pattern of language performance skills in repetition, comprehension, syntax, naming, and phonology
had changed, 70% of the children retained continued
signs of a language disorder. Sixty percent were in
special classes for the learning disabled or mentally
retarded.
Hall and Tomblin [40] followed two groups of
children first seen at 6 years of age into young adulthood, one group with impaired language and the
other with impaired speech but normal language.
Fifty percent of the language-impaired group continued to have speech and language difficulties, while
only one of the speech-disordered subjects was still
impaired. Scholastic test results demonstrated that
the language-impaired group had reading deficits
throughout school as well as lower educational
achievement.
Because few such children are noticeably impaired
in their expressive and receptive language skills past
8 years of age, it is often assumed that they catch up
to their peers in speech and language development.
However, those aspects of language which normally
develop during the school years are more subtle and
difficult to assess, and are not usually noted by parents or educators [ 8 8 ] . Language maturation during
these years includes the continued growth of expressive vocabulary, refinement of more complex sentence structures, and improved communication of
ideas and information to others [ 8 7 ] . Since standardized instruments are not available for evaluating
many of these aspects of linguistic development, little
attention is paid to such behaviors. Wiig and Semel
[88] found that adolescents having learning disabilities in school exhibited difficulties in word retrieval
and syntactic structure and performed poorly on verbal association tasks involving opposing and similar
meanings. Prospective studies of the subsequent
development of language-impaired preschool children into adolescence are not yet available.
Research Issues Concerning
Children’s Language Disorders
Dejay versus Deviance in Impaired
Language Development
The issue of whether or not children with impaired
language development acquire language in a fashion
similar to normal children, but at a slower rate, has
received considerable attention [601. Investigators generally contrast normal and language-impaired children who are at equivalent levels of language development but differ in chronological age. Subjects are
selected for each group who have the same mean
length of utterance (MLU), a valid measure of linguistic development during the first 5 years Ell]. The
normal and language-impaired groups are then compared to determine whether or not they differ in
certain linguistic skills. Answers to the delay versus
deviance question are not simple, but some general
trends can be identified.
Morehead and Ingram [631 found that languageimpaired children had fewer syntactic transformations in their sentence formations; the more
complex and infrequent syntactic constructions
rarely occurred in their speech in comparison with
younger normal children. For example, the impaired
subjects produced few questions. The investigators
concluded that the impaired subjects were only delayed in their acquisition of simple phrases and
sentences in comparison with normal subjects. They
had selective deficiencies, however, in acquisition of
the syntactic rules required for transforming simple
sentences into more complex constructions such as
questions.
Using the same approach, Freedman and Carpenter
[3 11 found no differences between normal children
and children with impaired language during the early
two-word stage of language development. Leonard,
Bolders, and Miller [54] matched normal and
language-impaired children on MLU and found only
that the language-impaired children were delayed in
comparison with normal; they performed like
younger normal children in their knowledge of word
meaning and semantic relationships.
In the 1960s, the acquisition of morphemes in
speech expression of normal children between 12
and 36 months of age was described [lll. The
applicability of these findings to language acquisition
in most normal children was demonstrated by devilliers and deVilliers [26] in a cross-sectional study of
large numbers of normal children at different age
levels. Johnston and Schery [46] studied morpheme
acquisition in language-impaired children and found
the same order as reported for normal children.
However, the language-impaired subjects did not
acquire these morphemes until they had reached a
higher level of language development in comparison
with normal children, supporting the conclusion that
these children are selectively impaired in the acquisition of morphology as well as syntax.
Menyuk and Looney [61] studied phrase and
sentence imitation in language-impaired children and
found that the impaired subjects had difficulties in
expanding the verb phrase part of their sentences.
They frequently deleted auxiliaries (such as will) and
modals (such as can and m a y ) and reduced negation of
a verb or auxiliary to a simple no, as in the following
examples.
Target Sentence
They won’t play with me.
I can’t sing.
He doesn’t have money.
She isn’t very old.
Impaired Imitation
They n o h o t play
with me.
I no can sing.
He no have money.
She not very old.
In a further study of sentence imitation, Menyuk [59]
found that language-impaired children could not
transform simple sentences into questions by inverting word order. During imitation, they produced
“When he will come?” instead of “When will he
come?” and “What that?” instead of “What is that?”
Although these cross-sectional studies indicate that
normal and language-impaired subjects follow the
same sequence of language acquisition, investigations
have shown that normal children differ in their order
of acquisition of certain linguistic forms [65]. Only
longitudinal studies of language acquisition in
language-impaired and normal children can determine the sequences followed by individual children.
Trantham and Pederson [84] have provided the
only longitudinal study contrasting a languageimpaired child with normal children between 11/2and
3 years of age, the time when most normal children
develop simple sentence structures beginning with
two-word utterances. The relationship between mean
sentence length and syntactic complexity (as measured by the Developmental Sentence Score [52])
found in the normal subjects differed from that
found in the language-impaired child. Between 24
and 36 months of age, the rate of growth of syntactic
and morphological complexity in the sentences spoken by the normal subjects surpassed the rate of increase in sentence length. The language-impaired
child showed a different developmental pattern; although his sentences were not reduced in length, his
utterances continued to be unmarked syntactically
and morphologically, and were unacceptable grammatically.
Subclasszjkation Needs
A major deficiency in the research on languageimpaired children has been poor control over subject
selection. Some investigators have included all children designated as “learning disabled” or “school failures” who are without frank sensory or severe
cognitive impairments. Others have selected as language impaired only children who have a normal
nonverbal IQ, are free from auditory, visual, neurological, or emotional disorders, and are significantly
Current Review: Ludlow: Children’s Language Disorders
49
delayed in language development. These latter criteria
usually eliminate over 50% of the children in classes
for the language impaired (Tallal P: personal communication, 1978). Less rigorous selection criteria
result in combined data that have little relevance to
individual children. On the other hand, when only
one well-defined group is studied, additional investigations are needed to determine whether the results
pertain to other types of children with impaired language.
Although language-impaired children differ considerably, little attention has been given to developing a system for classifying them into subgroups. In
fact, the marked diversity among language-impaired
children may be the reason that few classification
systems have been proposed. Myklebust [64] described four major types of “developmental aphasia,”
which resemble classic descriptions of acquired adult
aphasia: predominantly expressive, predominantly
receptive, mixed receptive and expressive, and central types with asymbolia. Further clinical descriptions of subgroups of language-impaired children were provided by de Ajuriaguerra et a1 [22].
However, these descriptions were not based on
quantitative test results and cannot be used by others
for subject description and selection.
Aram and Nation [3] made the first attempt at subclassification using factor analysis. They assembled a
small battery of tests assessing semantic, syntactic,
and phonological aspects of language comprehension, expression, and imitation. Factor analyses were
used to identify six patterns of language impairment
using standard scores derived from the subjects
studied. Because the tests were not previously standardized on the same population, however, others
will have difficulty identifying the same six patterns
of language performance in their subjects unless they
obtain Aram and Nation’s coefficients or derive standard scores for each test from a large pool of subjects. Work is needed to develop and standardize
comprehensive language batteries for assessing and
subgrouping language-impaired children. Wellvalidated language performance subclassification
profiles should subgroup these children, whether for
treatment or research purposes.
The prognostic importance of identifying subgroups of language-impaired children was demonstrated by Wolpaw, Nation, and Aram [90]. They
found different outcomes of preschool language impairment in the six subtypes of language-impaired
children when their subjects were examined five
years later, at 7 years of age. Some groups demonstrated marked shifts in their language behavior,
while others remained unchanged in their performance profiles. Thus, language-impaired children
must be subgrouped according to their patterns of
500
Annals of Neurology
Vol 7
No 6 June 1980
language impairment when the effects of different
treatment approaches are being investigated.
Auditory Processing Deficits
in Children’s Language Disorders
Auditory processing deficits for nonverbal and speechlike stimuli have been reported in a variety of language-impaired groups, including adult aphasics [ 14,
28, 771, reading-impaired children [4, 27, 681, and
language-impaired children [29, 57, 79-811. These
findings have been well confirmed. However, controversy surrounds the interpretation of these results. Some have implied that there might be a causal
relationship between nonverbal auditory processing
deficits and language comprehension disorders in
children. For example, after finding auditory processing deficits in language-impaired children for
both nonverbal and simulated speech signals, Tallal
and Piercy [82] concluded: “Dysphasic children are
not usually completely unable to utilize language and
they also differ individually in language ability. These
individual differences could be directly related to
differences in speed of auditory processing. The
greater the speed constraint, the fewer speech sounds
will be accurately processed and hence the greater
the language disorder.”
An alternative interpretation of such findings relates to the fact that rapid auditory processing abilities may be primarily left temporal lobe functions [77],
like language; thus, language and auditory processing
deficits may coincide in language-impaired children
simply because the two behaviors are controlled by
adjacent regions in the brain, both of which can be
affected by the same lesion or lesions.
Peronnet and Michel [66] examined the relationship between auditory evoked potentials and the presence or absence of aphasia in adults with left and
right hemisphere lesions. They reported a correspondence between hemianacousia (lack of auditory
evoked potentials in one hemisphere), dichotic
listening results, and the presence or absence of
a language disorder: “Right hemianacousia (left
temporal lesion) is usually disclosed in patients
suffering from language disturbances. In sensory
aphasia, the hemianacousia is very common, but in
motor aphasia it is rather rare. In any case, one finds
again a right ear extinction in the dichotic test. But a
right hemianacousia does not mean that there are
language disorders. We have seen patients who recover rapidly from a slight aphasia and still have abnormal AEP on the left side.”
The disassociation of an auditory processing impairment from a language disorder was recently
reported by Ludlow et a1 [58], who found severe auditory processing disorders in patients with Hunt-
ington’s disease. The patients were able to attend
to the auditory stimuli and perform the tasks but required longer interstimulus intervals than the aging
control group. Nevertheless, the patients had no
language disorder. In fact, verbal functions are usually spared in Huntington’s disease [ 131.
Although disorders of rapid auditory processing
are not the main cause of language disorders in children, they may contribute to language learning deficits in some cases. Frumkin and Rapin [32] studied
two subgroups of language-impaired children, one
impaired in speech articulation as well as language
and the other without speech articulation errors.
Only the group with abnormal speech articulation
had auditory processing deficits, compared with
normal controls. These subjects could not discriminate rapid changes in consonant-like stimuli. However, the language-impaired children without speech
impairments could identify rapid changes associated
with consonant-like stimuli but had difficulties identifying steady-state vowels. Thus, auditory processing
impairments may be associated with the occurrence
of speech articulation disorders in language-impaired
children, and not with all types of impaired language
development.
Similarly, Tallal, Stark, and Curtiss [83] reported
that the language-impaired subjects previously found
by Tallal and Piercy [80-821 to have disorders of
rapid auditory processing were impaired in speech
production in comparison with normal controls.
Since not all language-impaired children have speech
articulation disorders [3], these auditory processing
impairments may be present only in languagedisordered children who have speech articulation
impairments in addition to the usual syntactic and
morphological deficits occurring in such children.
The possible interactive effects of speech articulation impairments with the language encoding and decoding deficits of language-impaired children have
been further elucidated by the recent work of
Leonard and his associates [72]. They studied the
lexical development (expressive vocabulary) of
language-impaired children and found that subjects
avoided using words that contained sounds difficult
to produce: voiceless bilabials, palatal fricatives, and
affricates. These results imply that when disorders of
lexical expression are evident, they may reflect the
speech expression constraints of some languageimpaired children and are not due to difficulties in
learning lexical symbols per se. Whether these children also have auditory processing disorders which
may underlie their speech articulation impairments is
yet to be determined. Because of the probable interactions between development in the phonological,
syntactic, and semantic (lexical) language systems
during language acquisition, clear-cut answers con-
cerning the role of auditory processing deficits in language development will be difficult to obtain.
Cognitive Impairments Associated
with Impaired Language Development
The speculation that deficits in rapid auditory processing contribute to difficulties in developing language is only one of several hypotheses concerning
types of perceptual or cognitive deficits which affect
children impaired in learning language. Besides auditory processing deficits, language-impaired children exhibit other deficiencies when compared with
normal children of the same age: short-term memory
deficits [591, difficulties in processing rapidly occurring information presented in any modality [69],limited symbolic representation of meaning [45], and
speech production constraints [831. Studies demonstrating cognitive and perceptual deficits in languageimpaired children when compared with normal children similar in age, sex, and nonverbal I Q [9, 75,861
do not resolve the question of whether such deficits
are the consequence of delayed language development or could be the cause of difficulties in language
development. To examine this question, languageimpaired children should be compared with other
groups of developmentally impaired children who
are without language impairments to determine
whether they have similar perceptual or cognitive
difficulties.
In an attempt to study language separately from
other cognitive factors, Hermelin and O’Connor [44]
compared normal and mentally retarded children
with autistic children on tasks of attention, discrimination, perception, and encoding of motor, tactile,
visual, auditory, and verbal information. Although
the normal, mentally retarded, and autistic children
differed in their verbal abilities, all were equally capable of following motor cues. The autistic children
demonstrated rote memory skills and perception of
kinesthetic and motor cues at a level superior to their
mental age controls but were impaired in their interpretation and classification of visual and auditory
information. Bartak and colleagues [5,61 clarified the
relationship of these cognitive deficits to language
disorders in infantile autism by comparing the cognitive abilities of autistic and nonautistic languageimpaired children. Although the two groups had
similar auditory language comprehension disorders,
only the autistic group had other cognitive disorders
as evidenced by their difficulties with gesture and
imaginative play. Thus, autistic children may have
difficulties with acquiring symbols per se, while
language-impaired children only have problems with
segmenting and combining verbal symbols.
Investigators have reported that language-impaired
children have impairments in cognition when they
Current Review: Ludlow: Children’s Language Disorders 501
reach adolescence. Inhelder [45] studied these children’s abilities at the operational stage (between 5
and 7 years of age) and the figurative stage (between
9 and 11 years of age) of cognitive development.
During the operational stage, no differences were
found between language-impaired and normal children on tasks of rotation, numerical equivalence, and
sorting on the basis of color, size, and shape. However, marked differences were noted on tasks normally performed during the figurative stage involving
semantic class association and representational imagery. The language-impaired subjects violated semantic class constraints during item selection and were
deficient in solving nonverbal spatial problems.
Thus, language-impaired children may first show
cognitive deficits when more complex mental operations are required of them. Possibly, complex mental
operations, which emerge during adolescence, depend on the completion of normal language development. Whether or not language-impaired children
have cognitive deficits independent of, associated
with, or resulting from their language difficulties is
far from resolved.
The Neurological Bases
of Language Disorders in Children
Little research has been aimed at determining the
cause of language disorders in children, and few
hypotheses have been suggested. Longstanding disorders of language development which persist into
adolescence are difficult to explain in the context of
the neural plasticity demonstrated following prenatal
and postnatal lesions to the brain in animals and humans. Acquired lesions in the left hemisphere of
normally developing children produce a period of
aphasia followed by rapid and close to complete recovery [53]. Although the effects of prenatal lesions
in primates may not relate directly to the human
fetus, the neural plasticity reported by Goldman and
Galkin [39] was dramatic. They induced large cerebral lesions prenatally in monkeys, including regions
that in adult monkeys would have devastating effects
on learning behaviors. No deficits could be found in
learning behaviors throughout development, although cytoarchitectonic studies of the monkeys’
brains at puberty confirmed abnormalities in cortical
development. Neural migration toward excised regions had caused displacement of target cortical
structures, making comparisons with normal adult
brains difficult; the usual brain locations for certain
behaviors could not be assumed.
If these results apply to human brain development,
neither prenatal nor postnatal lesions could easily account for longstanding impairments in language
development. Alternatively, disordered development or lack of development of particular language-
502
Annals of Neurology
Vol 7
N o 6 June 1980
related brain regions could be a basis for language
disorders in children.
Goldman and Alexander [38] studied the brain
bases for behavior at different stages of development
in normal monkeys. Using regional cooling, they
found that different brain regions were responsible
for the same behavior at various times in development. Thus, the cortical and subcortical functioning
responsible for behavioral development underwent
considerable reorganization during maturation. If
these results pertain to human development, areas
of association cortex which are typically late to mature may not become involved in language until the
later stages of development, and any abnormality involving these regions may not become evident until
after the first year of life.
LANGUAGE LATERALIZATION. Infants have been
found to have innate speech perception mechanisms
which allow them to discriminate between speech
sounds at 1 month of age [201. Some such sounds
differ only in one feature: for example, the sound /b/
is similar to sound /p/ except that phonation begins
25 msec after the initiation of /b/ and is much later for
/p/. Human infants will categorize together all sounds
with phonation onsets between 0 and 25 msec and
discriminate these from all sounds with onset times
greater than 25 msec. This phenomenon is referred
to as categorical perception and provides evidence of
genetic programming for speech perception in infants. During language development, children begin
to assign labels to these categories and identify them
as speech sounds. Very little is known about this
developmental process since the same testing
methods cannot be used with young infants and children. Once children begin to develop language, they
attempt to label acoustic stimuli as speech sounds,
and their perception capabilities cannot be assessed
using the same simple discrimination procedures as
are used with infants.
Speech perception skills appear to develop
primarily within the left hemisphere. When speechlike stimuli are presented monaurally to infants, the
resulting auditory evoked potentials are greater in
the left than in the right hemisphere [62]. Gardiner
and Walter [36]have reported right-left asymmetries
in electroencephalographic responses to speech
stimuli in 6-month-old infants. They found left
hemisphere suppression of EEG power in a 4 Hz
centered frequency band, with similar suppression in
the right hemisphere for music. Thus, feature detector systems for speech perception may be predominantly in the left hemisphere at birth.
Evidence of hemispheric specialization in infancy
has altered previous conclusions about language
lateralization during development. Language devel-
opment is no longer believed to be a maturational
process in which both hemispheres participate and
the left eventually dominates. Woods and Teuber
[91]reported on a large number of cases of acquired
aphasia in children and found that only 6% occurred
as a result of a right hemisphere lesion. Thus, changes
in language lateralization may only be reflections of
the fact that as language develops, it does so in the
left hemisphere [481.
Anatomical evidence also indicates that the two
hemispheres may not have equal potential for language development. The top surface is greater in the
left temporal lobe than the right in nearly 60% of
newborns [89l, and the auditory “association” area
was often greater on the left than on the right in the
third trimester of fetal development [ 151. Such temporal lobe asymmetries may become greater during
maturation and differ from one individual to another
[35],but their relationship to language development
and function needs to be determined.
Although language may develop predominantly in
the left hemisphere, the right hemisphere seems to
have some language capability and contributes to
normal adult language functioning. Recent studies of
regional cerebral blood flow have demonstrated that
during speaking and listening, the right and left
hemispheres are almost equally active in normal
adults [ 5 11. The only differences were that increased
activity occurred in several separate and distinct areas
of the left hemisphere (such as Broca’s area and the
angular gyrus), while right hemisphere activation was
in one large, undifferentiated area of the temporoparietal region. Also, the supplementary motor cortex was more active on the left than on the right during speech [51]. It is not known, however, whether
the contributions of the two hemispheres differ during language performance.
The effects of hemispherectomies during childhood have indicated that the right hemisphere has
considerable language development capabilities in
the absence of an intact left hemisphere. Although
the immediate effects of left and right hemispherectomies in children are often similar [ 7 ] ,when they are
examined over ten years later as adults, individuals
who have had only a right or left hemisphere during
development provide evidence of the inherent
capabilities of each hemisphere for language development. Auditory language comprehension deficits
for syntactically complex materials have been found
in individuals who developed language with only a
right hemisphere intact [23]. Such deficits have not
been found in patients with only a left hemisphere
remaining, and left and right hemispherectomy
groups have equal phonemic and semantic abilities
when they reach maturity [24]. Thus, both hemispheres may have equal potential for acquiring the
phonemic, lexical, and semantic aspects of language
during development, but the left hemisphere is far
superior to the right in its capability of developing
the syntactic aspects of language.
The occurrence of language deficits in some cases
following lesions only in the right hemisphere [43]
suggests that the right side of the brain may contribute to normal adult language behavior. Minor but
permanent articulatory disorders accompany 4% of
right hemisphere lesions, while mild disorders involving syntactic transformations, sentence production, and lexical retrieval have been found following
parietal and parietooccipital lesions in the right
hemisphere when there is no evidence of left hemisphere damage [431.
Language recovery following left hemispherectomy in adulthood demonstrates the capacity of the
right hemisphere for some language functioning, although the previous long-term presence of an abnormally functioning left hemisphere may have altered the organization of language in the brain [12,
741. In adults with moderate to severe aphasia following a cerebrovascular accident involving the left
hemisphere, two investigators have used the Wada
test to study the speech production capacities of each
hemisphere [21, 471. Both reported worsening or
complete cessation of counting and naming in 80%
of the aphasics follo-ring right hemisphere injection
and continued speec.1 expression following anesthesia of the damaged left hemisphere.
Right hemisphere language functioning has been
studied extensively in patients who have undergone
complete cerebral commissurotomy for the relief of
intractable epilepsy. Specially fitted contact lenses
are used to assure occlusion of one visual field and
allow visual stimuli to be presented for unlimited durations during lengthy language testing of each
hemisphere “in isolation” 1931. T o assess the speech
perception and auditory comprehension capabilities
of each hemisphere, dichotic listening tasks are used
with unilateral visual presentation of the response
stimuli and subjects pointing with the homolateral
hand [931.
In the split-brain studies there have been no reports of speech expression by the right hemisphere
when disconnected from the left hemisphere [94].
Speech production occurred only during left hemisphere testing. However, the right hemisphere was
found to have good language comprehension; verbs
and nouns were easily understood in both written
and spoken form [94].The right hemisphere could
understand short sentences and phrases largely from
their vocabulary and not their syntactic structure. It
could not understand function words, identify sounds
contained in nonsense syllables, or rhyme words
[56],nor could it perform letter-to-sound matching
Current Review: Ludlow: Children’s Language Disorders 503
or pairing [94]. The right hemisphere seemed to use
word meaning primarily to understand written o r
spoken words and phrases, and was not capable
of phonetic analysis or recognizing meaningless
consonant-vowel syllables. Only the left hemisphere
could perform such tasks in split-brain patients [5 51.
Short-term memory restrictions were also found
for the right hemisphere when split-brain patients
were given a test highly sensitive to deficits in auditory comprehension [55, 941. Responses from the
right hemisphere were poorest on that part of the
token test which requires good short-term memory
but is not complex in syntactic structure [ l o , 25, 781.
Finally, the only language expression abilities found
on testing the right hemisphere were in one patient
who was able to arrange letters on a board with the
left hand to name objects presented to the left visual
field (right hemisphere) [37].
In conclusion, then, although language develops
predominantly in the left hemisphere, the right
hemisphere has the capacity, at the very least, to
develop representations of many language functions.
Only speech sound discrimination and syntactic
transformation seem t o be restricted to the left
hemisphere.
ACQUIRED LANGUAGE DISORDERS I N CHILDREN
(BETWEEN 3 AND 12 YEARS OLD). The pattern of
language performance of the right hemisphere found
in split-brain studies resembles the language performance of children with acquired aphasia following
left hemisphere lesions. Injury to the left hemisphere
in childhood produces language symptoms similar
to Broca’s aphasia [ l , 7, 911. Such children have
primarily expressive difficulties; they are nonfluent,
have speech articulation problems, make syntactic errors, and speak in a telegraphic style [ 4 2 ] .
Yeni-Komshian [92] conducted a study of recovery from acquired nonfluent aphasia in four children between the ages of 5 and 11 years following
severe head trauma inflicted on the left side. In three
cases there was destruction within the left language
area, but only for the fourth child did the neurosurgeon report “total destruction of the language area in
the left hemisphere.” O n dichotic listening tasks, the
first three children reported only from the right ear
throughout the recovery period, indicating that although the left language areas had been injured, left
hemisphere functioning continued to dominate the
right during performance of speech perception tasks.
It was only following substantial language recovery
that left ear reporting resumed in all three cases. In
the fourth patient, who had less recovery and who
continued to show marked residual speech and language deficits more than a year after the injury, reporting was predominantly from the left ear during
504 Annals of Neurology Vol 7 No 6 June 1980
recovery and following stabilization. Because the left
temporal primary auditory area was damaged in this
patient, left ear reporting cannot be interpreted as
demonstrating right hemisphere dominance for language. What is striking about the first three of these
prepubescent children is the strong tendency for
left language dominance even when brain lesions affected the left language areas.
Children’s language impairments accompanying
progressive seizure disorders present symptoms different from those just described. All reported children have exhibited fluent speech with frequent jargon and severely impaired auditory comprehension
[16, 50, 70, 731. Often there is evidence of bilateral
temporal lobe involvement, which could account for
the verbal agnosia accompanying this syndrome. It
may be that a severe language comprehension disorder in children can occur only when there is bilateral
involvement of the temporal lobes. Based on observations of acquired aphasia in children and the capacity of the right hemisphere for developing language comprehension, it is difficult to explain severe
acquired language comprehension deficits in children
without bilateral temporal lobe involvement.
A unique case of language delay was that of a child
isolated from infancy to 13% years with virtually no
language stimulation [ 181. Following discovery and
early language therapy, the girl began to acquire vocabulary with incredible speed.
. . . after her emergence (from isolation), her ability to generalize specific objects to general categories was very rapid.
She seemed to learn simultaneously the generic terms and
the names for the members of a class. Tory, the name of the
household dog, was reserved for him but all other dogs
were immediately recognized as dogs as, of course, was
Tory. One did not need to teach her, as she learned the
words for dress, socks, shoes, tie, coat, sweater, that these were
all clothes, nor that a toy which moved was not animate
[191.
But after two years of intensive therapy, the child
retained marked difficulties in language expression
although she continued to acquire additional vocabulary. H e r phonological system was immature, her
spontaneous speech was almost devoid of syntax, and
she communicated primarily using single words [IS].
Tachistoscopic, evoked potential, and dichotic
studies all indicated that language was controlled by
the right hemisphere [ 181. Although possible head
trauma and prolonged malnutrition may have contributed to this case of limited exposure to language
prior to puberty, the occurrence of postpubertal
lateralization of language in the right hemisphere
may indicate that left hemisphere dominance for language development weakens with age.
Directions for Research
Recently, clinicians have reported successes in
teaching language-impaired children to communicate
by using visual symbol systems such as American
Sign Language or Bliss symbols to represent lexical
information [8, 30,491. There have also been reports
of oral expression appearing in these children along
with symbol acquisition [33]. Although such cases
need to be substantiated through careful study, they
indicate that these children do not have an associative
verbal learning disorder or difficulty acquiring lexical
information, but rather problems with learning certain aspects of language through the auditory channel.
A reduction in size of the auditory association area
in the left hemisphere has been found in the brain of
a dyslexic subject [34, 351. Others have reported diminished left hemisphere size in some languagedisabled children [41]. Language-impaired children
are particularly impaired in syntax and morphology,
abilities which are dependent upon an intact left
hemisphere [46, 61, 631. Further, the deficits in nonverbal rapid auditory processing characteristic of
language-impaired children [80-821 indicate a failure
to develop the acoustic feature detector mechanisms
normally present in the left hemisphere at birth.
Thus, impaired language development is most likely
due to abnormal or delayed development of left
temporoparietal functioning. The strong tendency
for language to be localized in the left hemisphere
may account for the right hemisphere not becoming
dominant in such cases. Transfer of dominance to the
right hemisphere may be much less likely when the
left hemisphere is developmentally impaired but still
functioning than when it is largely destroyed following hemispherectomy or traumatic lesions.
Some evidence suggests that the left and right
hemispheres mature at different rates, with the left
hemisphere developing earlier and at a more rapid
rate than the right [17, 851. An increasing capacity of
the right hemisphere for language functioning with
age may be responsible for the relatively normal but
delayed development of right hemisphere language
functions in language-impaired children. Semantic
and lexical knowledge are more easily acquired, and
auditory comprehension skills exceed the development of expressive language skills. Thus, the
symptoms in language-impaired children may reflect
defective development of the left temporoparietal
region along with the normally late maturation of
semantic and lexical language comprehension skills
in the right hemisphere. Some evidence, although
tenuous, indicates that the role of the right hemisphere in speech perception may be equal to that of
the left in language-impaired children. Two dichotic
listening studies found a lack of left or right ear ad-
vantage in language-impaired children, while normal
children and those with impaired speech articulation
demonstrated a significant right ear advantage [67,
7 13. Research is needed to determine which areas of
the brain are active during various types of language
performance in normal and language-impaired children. Different patterns of abnormal functioning may
occur in the left and right hemispheres at various
times during development since the symptoms in
these children change with age. Although language
development eventually catches up to normal in such
children, continued left hemisphere deficits may be
responsible for their subsequent severe reading and
writing problems [90] and for their more subtle
deficits in complex language functions at 9 years of
age [881.
Dr Herbert Lansdell provided advice and suggestions during the
development of this manuscript.
Publication of this article has been subsidized by the National Institute of Neurological and communicative Disorders and Stroke.
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