Language Development and Communication Disorders

Receptive Language Development

The peripheral auditory system is mature by 26 wk gestation, and the fetus responds to and discriminates speech sounds. Anatomic asymmetry in the planum temporale , the structural brain region specialized for language processing, is present by 31 wk gestation. At birth, the full-term newborn appears to have functionally organized neural networks that are sensitive to different properties of language input. The normal newborn demonstrates preferential response to human voices over inanimate sound and recognizes the mother's voice, reacting stronger to it than to a stranger's voice. Even more remarkable is the ability of the newborn to discriminate sentences in their “native” (mother's) language from sentences in a “foreign” language. In research settings, infants of monolingual mothers showed a preference for only that language, whereas infants of bilingual mothers showed a preference for both exposed languages over any other language.

Between 4 and 6 mo, infants visually search for the source of sounds, again showing a preference for the human voice over other environmental sounds. By 6 mo, infants can passively follow the adult's line of visual regard, resulting in a “joint reference” to the same objects and events in the environment. The ability to share the same experience is critical to the development of further language, social, and cognitive skills as the infant “maps” specific meanings onto his or her experiences. By 8-9 mo, the infant can actively show, give, and point to objects. Comprehension of words often becomes apparent by 9 mo, when the infant selectively responds to his or her name and appears to comprehend the word “no.” Social games, such as “peek-a-boo,” “so big,” and waving “bye-bye” can be elicited by simply mentioning the words. At 12 mo, many children can follow a simple, 1-step request without a gesture (e.g., “Give it to me”).

Between 1 and 2 yr, comprehension of language accelerates rapidly. Toddlers can point to body parts on command, identify pictures in books when named, and respond to simple questions (e.g., “Where's your shoe?”). The 2 yr old is able to follow a 2-step command, employing unrelated tasks (e.g., “Take off your shoes, then go sit at the table”), and can point to objects described by their use (e.g., “Give me the one we drink from”). By 3 yr, children typically understand simple “wh-” question forms (e.g., who, what, where, why). By 4 yr, most children can follow adult conversation. They can listen to a short story and answer simple questions about it. A 5 yr old typically has a receptive vocabulary of more than 2000 words and can follow 3- and 4-step commands.

Expressive Language Development

Cooing noises are established by 4-6 wk of age. Over the 1st 3 mo of life, parents may distinguish their infant's different vocal sounds for pleasure, pain, fussing, tiredness, and so on. Many 3 mo old infants vocalize in a reciprocal fashion with an adult to maintain a social interaction (“vocal tennis”). By 4 mo, infants begin to make bilabial (“raspberry”) sounds, and by 5 mo, monosyllables and laughing are noticeable. Between 6 and 8 mo, polysyllabic babbling (“lalala” or “mamama”) is heard, and the infant might begin to communicate with gestures. Between 8 and 10 mo, babbling makes a phonologic shift toward the particular sound patterns of the child's native language (i.e., they produce more native sounds than nonnative sounds). At 9-10 mo, babbling becomes truncated into specific words (e.g., “mama,” “dada”) for their parents.

Over the next several months, infants learn 1 or 2 words for common objects and begin to imitate words presented by an adult. These words might appear to come and go from the child's repertoire until a stable group of 10 or more words is established. The rate of acquisition of new words is approximately 1 new word per week at 12 mo, but it accelerates to approximately 1 new word per day by 2 yr. The first words to appear are used primarily to label objects (nouns) or to ask for objects and people (requests). By 18-20 mo, toddlers should use a minimum of 20 words and produce jargon (strings of word-like sounds) with language-like inflection patterns (rising and falling speech patterns). This jargon usually contains some embedded true words. Spontaneous 2-word phrases (pivotal speech), consisting of the flexible juxtaposition of words with clear intention (e.g., “Want juice!” or “Me down!”), is characteristic of 2 yr olds and reflects the emergence of grammatical ability (syntax).

Two-word, combinational phrases do not usually emerge until children have acquired 50-100 words in their lexicon. Thereafter, the acquisition of new words accelerates rapidly. As knowledge of grammar increases, there is a proportional increase in verbs, adjectives, and other words that serve to define the relation between objects and people (predicates). By 3 yr, sentence length increases, and the child uses pronouns and simple present-tense verb forms. These 3-5 word sentences typically have a subject and verb but lack conjunctions, articles, and complex verb forms. The Sesame Street character Cookie Monster (“Me want cookie!”) typifies the “telegraphic” nature of the 3 yr old's sentences. By 4-5 yr, children should be able to carry on conversations using adult-like grammatical forms and use sentences that provide details (e.g., “I like to read my books”).

Variations of Normal

Language milestones have been found to be largely universal across languages and cultures, with some variations depending on the complexity of the grammatical structure of individual languages. In Italian (where verbs often occupy a prominent position at the beginning or end of sentences), 14 mo olds produce a greater proportion of verbs compared with English speaking infants. Within a given language, development usually follows a predictable pattern, paralleling general cognitive development. Although the sequences are predictable, the exact timing of achievement is not. There are marked variations among normal children in the rate of development of babbling, comprehension of words, production of single words, and use of combinational forms within the first 2-3 yr of life.

Two basic patterns of language learning have been identified, analytic and holistic. The analytic pattern is the most common and reflects the mastery of increasingly larger units of language form. The child's analytic skills proceed from simple to more complex and lengthy forms. Children who follow a holistic or gestalt learning pattern might start by using relatively large chunks of speech in familiar contexts. They might memorize familiar phrases or dialog from movies or stories and repeat them in an overgeneralized fashion. Their sentences often have a formulaic pattern, reflecting inadequate mastery of the use of grammar to flexibly and spontaneously combine words appropriately in the child's own unique utterance. Over time, these children gradually break down the meanings of phrases and sentences into their component parts, and they learn to analyze the linguistic units of these memorized forms. As this occurs, more original speech productions emerge, and the child is able to assemble thoughts in a more flexible manner. Both analytic and holistic learning processes are necessary for normal language development to occur.

Epidemiology

Disorders of speech and language are very common in preschool-age children. Almost 20% of 2 yr olds are thought to have delayed onset of language. By age 5 yr, approximately 6% of children are identified as having a speech impairment, 5% as having both speech and language impairment, and 8% as having language impairment. Boys are nearly twice as likely to have an identified speech or language impairment as girls.

Etiology

Normal language ability is a complex function that is widely distributed across the brain through interconnected neural networks that are synchronized for specific activities. Although clinical similarities exist between acquired aphasia in adults and childhood language disorders, unilateral focal lesions acquired in early life do not seem to have the same effects in children as in adults. Risk factors for neurologic injury are absent in the vast majority of children with language impairment.

Genetic factors appear to play a major role in influencing how children learn to talk. Language disorders cluster in families. A careful family history may identify current or past speech or language problems in up to 30% of first-degree relatives of proband children. Although children exposed to parents with language difficulty might be expected to experience poor language stimulation and inappropriate language modeling, studies of twins have shown the concordance rate for low language test score and/or a history of speech therapy to be approximately 50% in dizygotic pairs, rising to over 90% in monozygotic pairs. Despite strong evidence that language disorders have a genetic basis, consistent genetic mutations have not been identified. Instead, multiple genetic regions and epigenetic changes may result in heterogeneous genetic pathways causing language disorders. Some of these genetic pathways disrupt the timing of early prenatal neurodevelopmental events affecting migration of nerve cells from the germinal matrix to the cerebral cortex. Several single nucleotide polymorphisms (SNPs) involving noncoding regulatory genes, including CNTNAP2 (contactin-associated-protein-like-2) and KIAA0319 , are strongly associated with early language acquisition and are also believed to affect early neuronal structural development.

In addition, other environmental, hormonal, and nutritional factors may exert epigenetic influences by dysregulating gene expression and resulting in aberrant sequencing of the onset, growth, and timing of language development .

Pathogenesis

Language disorders are associated with a fundamental deficit in the brain's capacity to process complex information rapidly. Simultaneous evaluation of words (semantics), sentences (syntax), prosody (tone of voice), and social cues can overtax the child's ability to comprehend and respond appropriately in a verbal setting. Limitations in the amount of information that can be stored in verbal working memory can further limit the rate at which language information is processed. Electrophysiologic studies show abnormal latency in the early phase of auditory processing in children with language disorders. Neuroimaging studies identify an array of anatomic abnormalities in regions of the brain that are central to language processing. MRI scans in children with specific language impairment (SLI) may reveal white matter lesions and volume loss, ventricular enlargement, focal gray matter heterotopia within the right and left parietotemporal white matter, abnormal morphology of the inferior frontal gyrus, atypical patterns of asymmetry of language cortex, or increased thickness of the corpus callosum in a minority of affected children. Postmortem studies of children with language disorders found evidence of atypical symmetry in the plana temporale and cortical dysplasia in the region of the sylvian fissure. In support of a genetic mechanism affecting cerebral development, a high rate of atypical perisylvian asymmetries has also been documented in the parents of children with SLI.

Clinical Manifestations

Primary disorders of speech and language development are often found in the absence of more generalized cognitive or motor dysfunction. However, disorders of communication are also the most common comorbidities in persons with generalized cognitive disorders (intellectual disability or autism), structural anomalies of the organs of speech (e.g., velopharyngeal insufficiency from cleft palate), and neuromotor conditions affecting oral motor coordination (e.g., dysarthria from cerebral palsy or other neuromuscular disorders).

Intellectual Disability

Most children with a mild degree of intellectual disability learn to talk at a slower-than-normal rate; they follow a normal sequence of language acquisition and eventually master basic communication skills. Difficulties may be encountered with higher-level language concepts and use. Persons with moderate to severe degrees of intellectual disability can have great difficulty in acquiring basic communication skills. About half of persons with an intelligence quotient (IQ) of <50 can communicate using single words or simple phrases; the rest are typically nonverbal.

Autism Spectrum Disorder

A disordered pattern of language development is one of the core features of ASD (see Chapter 54 ). The language profile of children with ASD is often indistinguishable from that in children with SLI or SPCD. The key characteristics of ASD that distinguish it from SLI or SPCD are lack of reciprocal social relationships; limitation in the ability to develop functional, symbolic, or pretend play; hyper- or hyporeactivity to sensory input; and an obsessive need for sameness and resistance to change. Approximately 40% of children with ASD also have intellectual disability, which can limit their ability to develop functional communication skills. Language abilities can range from absent to grammatically intact, but with limited pragmatic features and odd prosody patterns. Some individuals with ASD have highly specialized, but isolated, “savant” skills, such as calendar calculations and hyperlexia (the precocious ability to recognize written words beyond expectation based on general intellectual ability). Parents report regression in language and social skills ( autistic regression ) in approximately 20–25% of children with ASD, usually between 12 and 36 mo of age. The cause of the regression is not known, but it tends to be associated with an increased risk for comorbid intellectual disability and more severe ASD ( Fig. 52.1 ).

Asperger Syndrome

Asperger syndrome is characterized by difficulties in social interaction, eccentric behaviors, and abnormally intense and circumscribed interests despite normal cognitive and verbal ability. Affected individuals may engage in long-winded, verbose monologs about their topics of special interest, with little regard to the reaction of others. Adults with Asperger syndrome generally have a more favorable prognosis of than those with “classic” autism. Prior to 2013, Asperger syndrome was classified as distinct from autism; however, DSM-5 no longer recognizes Asperger as a separate neurodevelopmental disorder. More severely affected individuals are now considered to be at the “high functioning” end of the autism spectrum (see Chapter 54 ), whereas mildly impaired individuals may be diagnosed with SPCD.