The ability to communicate at a very high level by a wide range of modalities—including spoken language, facial expression, tone of voice, and gesture—is a uniquely human ability. It is usually acquired early in life as a result of not only exposure but also the evolved readiness to learn to communicate. Disorders of communication can arise as disruptions in this process either in association with other problems or as more isolated and specific difficulty. Speech is one important part of the more general communication domain (see Figure 8.1 and Box 8.1). Communication also includes written communication and the use of symbols as in written language or manual sign, both of which can be used to convey information quite efficiently and durably (e.g., the hieroglyphics of the pharaohs are still readable today). Animals can communicate, for example, to signal territory, danger, attract a mate, and so forth, and some are very perceptive indeed, but they do not have the same capacities for spoken language or written communication that people do to express ideas, thoughts, and feelings.

These utterances are often totally new, that is, they are created without being previously heard. Speech is one mode of language; writing provides another form of expression. For individuals who have already learned to speak and write but then suffer impediments to speech, for example, following a stroke, written communication can be a substitute. The situation is more complicated when difficulties occur in the developmental period, that is, before these various forms of communication are established.

The investigations of Broca and Wernicke led to important discoveries about the brain localization of language functions as they studied aphasia in adults. In this approach (based largely on adults with brain damage), recognition of words came in Wernicke’s area in the left temporoparietal junction and then language production occurred via Broca’s area in the left inferior frontal gyrus. But with the advent of more sophisticated imaging techniques, including MRI, it is clear that this model is very much an oversimplified one (see Hagoort, 2019, for a recent and comprehensive summary).

Clinical work focused on children began in the 1900s as psychologists, speech therapists, and educators began to study similarities and differences in adults with language problems, for example, poststroke aphasia as compared to children with language problems; they also began to work on the best teaching methods. Interest in children’s language as a field of study began to increase, for example, for children who were deaf or who exhibited severe language

problems. Attempts were made to start differentiating various types of child language-speech problems. Around the same period of time, interest in child language in its own right began to increase, for example, with Piaget’s work on children’s thinking and Chomsky’s work on transformational thought (see Schoen & Paul, 2018).

In the past, the term language disorder was used, but now it has been replaced by communication disorder to emphasize that problems are not limited simply to spoken language. Table 8.1 explains some key concepts/terms used in relation to language development and disorders. It should be noted that there are some important differences as well as similarities between major diagnostic systems. In the DSM-5 approach (APA, 2013), substantial changes were made from the previous DSM-IV (APA, 2000) diagnoses of Expressive Language Disorder and Mixed Receptive-Expressive Language Disorder. The new DSM-5 diagnostic categories include the following:

The DSM-5 approach builds on DSM-IV with some important differences. For example, with language disorder, the emphasis on whether receptive or expressive skills are more impaired is no longer made. The new social pragmatic disorder category reflects an awareness that some (if not many) individuals with problems on the autism spectrum might no longer receive an ASD diagnosis, although they still need service; the relationships and distinctions between SCD and autism remain the topic of debate (Jackson & Volkmar, 2019).

In contrast to DSM-5, the American Speech Hearing Association (1993) defines a language disorder as an impairment in “comprehension and/or use of a spoken, written, and/or other symbol system. The disorder may involve (1) the form of language (phonology, morphology, and syntax), (2) the content of language (semantics), and/or (3) the function of language in communication (pragmatics), in any combination” (1993, p. 40). Some clinicians have preferred to use the term developmental language disorder (i.e., to contrast this disorder from that of adults with onset of language problems in later life, i.e., well after language has previously been acquired). This view (more like that used in DSM-IV) makes a distinction between (1) mixed receptive/expressive disorders, which impair phonology, syntax, and semantics that lead to problems in expression and understanding; (2) expressive disorders, that is, when comprehension is intact but there are major problems in the production of language; and (3) higher order problems of language involving pragmatic (social language), semantic (the meaning of language), and discourse and conversation with adequate comprehension affecting spoken language (phonology; Rapin, 1996). In all these cases, some degree of functional impairment is required.

Language disorders can exist in isolation but are frequently associated with other developmental disorders. If the focus is on specific language impairments (SLIs), there is strong evidence for neurobiological factors in syndrome pathogenesis. For example, there is increased rate of concordance in monozygotic than in dizygotic twins; similarly, the risk for family members is increased. Although much speculation has centered on the role of environmental factors, the strongest associations are with lower socioeconomic status, larger family size, later birth order, and recurrent otitis media—all factors that deprive the child of language input at a critical stage in learning (Boxes 8.2 and 8.3).

If the focus is broadened beyond isolated language problems, the association with problems in overactivity and inattention is frequent. Of course, the ability to acquire language helps the child provide an inner narrative that facilitates focus, and conversely, a lack of language ability naturally may lead to difficulties with organization and attention. The nature of the role of cognitive factors has been debated, for example, some investigators suggest that the language difficulties reflect a more general deficit in symbolic representation; speed of responding also may contribute to problems in information processing. It is also the case, of course, that some individuals will simply be at the lower end of the normal range in language abilities. Other approaches have focused more specifically on difficulties in auditory information processing particularly relative to the need for rapid processing of the kind needed for speech processing and language segmentation (i.e., hearing the individual words within the stream of speech).

Perhaps 10% to 15% of children younger than 3 years of age will be delayed in language development (Schoen & Paul, 2018). Most of these (50%-80%) will eventually acquire language skills within the normal range, but some show persistent language difficulties into adulthood. As a general rule, language problems that persist after age 4 clearly warrant clinical evaluation (Tomblin et al., 1997).

Given the differences in definition and method, it is not surprising that estimates of the prevalence of specific language disorders vary widely. Expressive problems are more common than receptive ones. Boys are several (3-5) times more likely than girls to have language disorders. Data on the epidemiology of the new SCD category are quite limited, but given the likely overlap with the older PDD-NOS concept in DSM-IV, a rate of perhaps 1% is likely. The prevalence of speech sound disorder is greatest in toddlers and decreases to 1% to 2% as children enter school and is uncommon by the end of high school (Schoen & Paul, 2018). There is a male predominance and also familial aggregation. Stuttering also occurs more commonly in males with a general population rate of around 1%. Many younger children who stutter go on, as adults, to have fluent speech. Again, familial aggregation is noted and many
who stutter as adults have problems with anxiety. Various methods (aggregation, pedigree, twin, adoption, and linkage studies) have provided clear evidence of genetic influences on language disorder. Complementary work also points to environmental input as a key factor that likely contributes to familial aggregation. Speech-language-communication problems often co-occur in association with a number of disorders (see Table 8.2).

Environmental and cultural factors are also important. Children reared in bilingual households will learn both languages without difficulty at a young age as long as parents are consistent (e.g., one parent speaks one language and the other parent does the other, or the native language is spoken only at home). But these children may be somewhat delayed in becoming fluent in them. Assessment by an experienced speech-language pathologist using standard measures of language communication or intelligence should take such issues into account (Paul & Lyons, 2018).

Neuroimaging and other neuroscience approaches have focused on differences in brain processing of language (Badcock et al., 2012). Later in life, acquired disorders, for example, aphasia after damage to Broca’s area following a stroke, have clarified some aspects of localization of language process in the brain. The association of language problems with neurologic soft signs is further suggestive of brain involvement. Functional and structural differences have been documented in children with language disorders in those regions known to be involved in language progressing. For typically developing persons, the brain is asymmetric, with language structures tending to be larger in the left hemisphere; children with language problems typically have more symmetric hemispheres. Adults with language difficulties are more likely to have an extra sulcus in Broca’s area in either brain hemisphere, although it must be emphasized that no one pattern of brain architecture has been consistently found. Onset of seizures in childhood may be associated with some language loss. Other acquired language problems can arise because of head injury or similar insults to the developing brain. Language delays can arise as a result of deafness or fluctuating hearing levels, for example, with recurrent ear infections. Exposure in utero to certain drugs or toxins may also be associated with language problems in the child. Stuttering clearly has a strong biologic component with involvement of aspects of both the central and peripheral nervous
system, with anxiety playing a prominent role as well (see Box 8.4 for a case examples of stuttering). There is also a genetic component with increased risk in first-degree relatives.