All of a sudden, it seems that everyone is talking about something called "nonverbal learning disability" or NLD. Speech-language pathologists receive referrals where NLD is listed as the diagnosis. Psychologists and teachers discuss NLD at coffee and at team meetings. For many SLPs, this is an unfamiliar diagnostic term, and its use raises several questions. Clinicians ask: What is nonverbal learning disability? What causes it? How do I recognize it? If it's nonverbal, what does it have to do with me? Is there a communication problem? How should I assess these children? What do I do about it? Unfortunately, since research has lagged behind the rapid rise in popularity of this diagnostic category, definitive answers to these questions are in short supply, but this article is an attempt to provide at least partial answers to some of them.
What Is NLD and What's It Have to Do With Me?
NLD is a subtype of learning disability that has been the subject of intense scrutiny by Byron Rourke, a neuropsychologist at the University of Windsor. He and his colleagues (see references) have identified two reliable subtypes of learning disability. They call one group Basic Phonological Processing Disorder. Children in this category fit well within our traditional views of language learning disability or specific language impairment. These are children who are characterized by poor speech and language skills and extraordinary difficulty with reading and writing, but who demonstrate relatively preserved nonverbal problem solving. Generally, their performance IQ is within normal limits, but verbal IQ scores are significantly depressed.
Rourke calls the other group Nonverbal Learning Disability. Children placed in this group display a profile of skills that is largely opposite from the first group. Verbal IQ scores, for example, are well within normal limits, whereas nonverbal IQ lags behind. These children have difficulty with nonverbal problem solving, visual-spatial-organizational skills, tactile perception, and complex psychomotor behavior but, on the surface at least, they appear to have good language skills. They talk (often excessively), they use a variety of sentence structures, they can memorize and repeat vast amounts of verbal material, and they demonstrate average to above-average abilities in single-word reading and spelling.
At first glance, it may seem that SLPs have no role to play in the management of these children. Despite their verbal fluency, however, children and adolescents with NLD exhibit substantial communication and language problems. The key to understanding their communication dysfunction is that their apparent competence in language is superficial. Whenever situations call for deep or elaborated comprehension, use of contextual information, or sophisticated social competence, children with NLD are likely to perform poorly, demonstrating just how shallow their abilities are.
According to Rourke, NLD manifests itself to some degree whenever significant amounts of white matter in the brain are destroyed or dysfunctional. Specifically, he proposes that damage to the white matter in the right cerebral hemisphere is particularly influential. As plausible as this model may be, it is far from definitive. Other authors have suggested that the symptoms seen in NLD also may have their roots in deficits in working memory (neither a specific right-hemisphere nor white-matter function) or in executive processes (generally spoken of as a frontal-lobe function). At the very least, confirmation of Rourke's hypothesis awaits imaging studies such as fMRI.
Dimensions of Language in NLD
In spite of the newfound popularity of NLD as a diagnosis, speech and language skills in this population have remained largely unexplored, at least in any systematic way. Anecdotal accounts are virtually our only sources of information at this time. Research establishing empirical bases to substantiate existing clinical accounts is sorely needed.
Language often is divided into the domains of form, content, and use. Three dimensions of language structure—phonology, morphology, and syntax—are included in the broader domain of language form. Phonology, which includes mastery of the sound system, is reported to be intact in children with NLD. The dimension of morphology, which deals with inflectional word marking, also is reported to be adequate. Likewise, syntax, including the formation of complete sentences and the use of various sentence types, is described as age-appropriate. Although none of these dimensions have been subject to detailed empirical examination, case reports and anecdotal accounts report no glaring deficits as judged by conversational partners. Thus, while evidence would be useful for validating clinical impressions, it seems likely that language structure is not an area of dysfunction for these children.
The status of language content, or semantics, is less clear. Children with NLD, for example, may exhibit large and sophisticated vocabularies. Being able to use a large number of sophisticated words, however, does not automatically ensure that children fully understand them. For example, one young adult in my research was engaged in a referential communication task where she was required to describe a certain geometric shape. She described it as "a unilateral triangle." While it's possible she could have confused the isosceles triangle on the stimulus card for an equilateral triangle, it was definitely not a single-sided shape as the word "unilateral" denotes.
Ultimately, says Rourke, "although children with NLD tend to be verbose, there is relatively little in the way of meaningful content that is conveyed in their discourse" (see Rourke & Tsatsanis, p. 37). Others have described this phenomenon as "cocktail party language."
Difficulties in comprehension become more apparent as the child grows older, and conversational interactions begin to demand the ability to employ contextual cues. In addition, the appreciation of humor, irony, idioms, or metaphor requires an adroit manipulation of literal and nonliteral meanings. This requires elaborated semantic networks that allow for a word to be connected with a variety of concepts. With only a superficial understanding of language, the child with NLD is unlikely to appreciate figurative language or abstract meaning. Bishop cites the example of a child who was told to "watch your hands" when using scissors and proceeded to stare at his fingers.
One explanation for relatively superficial semantic knowledge is the over-reliance that these children apparently place on learning through auditory and verbal means. Perhaps many of the words of the child with NLD are "fast mapped" rather than fully understood. This too is a reasonable area for systematic research.
The most deficient domain of language in children with NLD is reported to be language use or pragmatics. Pragmatics refers to the appropriate social use of language and includes the ability to generate language to accomplish a wide variety of specific social purposes (e.g., requesting objects, requesting information, commenting, greeting, etc.) as well as the ability to manage conversations successfully (e.g., initiating interactions and introducing topics, taking turns, maintaining and building on topics, recognizing and repairing conversational breakdowns, etc.).
Again, none of these areas has been the subject of empirical investigation but, in anecdotal accounts, it is the discourse skills or conversational management abilities of children with NLD that are reported to be seriously impaired. According to Rourke and Tsatsanis, "The discourse of children with NLD is often rambling, marked by minimal structure, organization and cohesion; it tends to be tangential, repetitive, and of a monotonous and straightforward nature, containing little conceptual content. Verbalizations are often loose and characterized by intrusions, embellishments, and confabulations" (pp. 37–38).
In addition, speakers with NLD often are characterized as verbose. Other examples of pragmatic difficulties that may occur include frequent use of stereotyped expressions such as "by the way" or "actually," an inability to read or use facial expressions or tone of voice, difficulties in using facial expression and gestures to express feelings, problems with appropriate speech prosody resulting in a lack of affective modulation in language, and abrupt topic shifts. At present, we are unable to say which of the above behaviors is more or less characteristic of children with NLD, or indeed whether other pragmatic language features, not listed above, might be more associated with the phenomenon. The research to establish those kinds of descriptions remains to be done.
Is This a New Phenomenon?
There's no reason to believe that NLD is a new phenomenon. It may be that this is just a new way of thinking about and categorizing children that we already see. Although Rourke's NLD syndrome is gaining considerable ground in clinical use, it is not yet listed as a diagnostic category in standard taxonomies of diseases and developmental disorders such as the International Classification of Diseases (ICD-10). This will likely not occur until a substantial body of evidence from a variety of independent sources has investigated and validated the initial descriptions.
At present, at least in terms of speech and language symptomatology, the descriptions of NLD bear considerable similarity to those associated with a variety of other conditions, such as semantic-pragmatic disorder, pragmatic language impairment, high-functioning autism, Asperger's syndrome, and others. It is possible that what is described in educational terms as nonverbal learning disability may be what we describe in speech-language terms as pragmatic language impairment.
A detailed discussion of suggestions for assessment and intervention is beyond the scope of this article, but I do have one or two suggestions to add to the clinician's arsenal.
In terms of assessment, if anecdotal accounts of the language deficits associated with NLD are correct, then pragmatic language skills present the greatest problem. Adequate assessment of pragmatics is notoriously difficult. No doubt this will always be true due to the contextual nature of pragmatic language competence. By definition, standardized measures can only assess behavior in strictly controlled situations. Because appropriate pragmatic behavior depends upon successfully adjusting to shifting social circumstances, it is difficult to build comprehensive standardized pragmatic language assessments.
In addition, many of the instruments that have been developed (e.g., the Test of Pragmatic Skills, etc.) quantify pragmatic skill in relation to developmental norms rather than focusing on qualitative abnormalities in communication. In order to evaluate pragmatic features of the sort that are reported to typify the population with NLD (e.g., verbosity, inappropriate content, etc.), it's important to assess behaviors that are difficult to elicit in test situations and that may be rare, but salient, in occurrence. Dorothy Bishop has developed such a tool. She calls it the Children's Communication Checklist (CCC; see references).
The CCC is a 70-item checklist that may be completed by parents, caregivers, or service providers. The respondent is asked to rate statements on nine dimensions of communication, five of which focus on aspects of pragmatic communication that are reported as clinically significant (e.g., inappropriate initiations, difficulties with coherence, stereotyped conversation, difficulties in using conversational context, and difficulties in establishing conversational rapport). Examples of the items include: "Talks repetitively about things that no one is interested in" and "It is sometimes hard to make sense of what he is saying because it seems illogical or disconnected."
Designed to assess "pragmatic language impairment," the CCC nonetheless evaluates exactly the types of pragmatic language errors that have been attributed to NLD. Respondents rate each of the 70 items as to whether the statement definitely applies, applies somewhat, or doesn't apply to the child in question. A pragmatic composite score is calculated from the ratings applied on the five pragmatic subscales. Bishop found that this composite score successfully discriminated between children with a diagnosis of specific language impairment and those whose communication problems were pragmatic. The CCC seems to me to be an invaluable tool in the quantification of pragmatic language impairment in the population with NLD and others.
With regard to intervention, until we have evidence that suggests otherwise, clinicians are encouraged to treat these children as they treat others with pragmatic language impairment. If, as expected in this population, conversational management emerges as an area of need, the SLP will need to develop ways to help the child with NLD acquire the relevant skills and use them appropriately. Careful scrutiny of the resources available on pragmatic language intervention should yield several ideas (see Brinton & Fujiki's book for some particularly helpful tips).
In terms of semantic deficit, it seems important to promote active processing of information rather than the rapid but superficial acquisition that may be occurring most of the time. Suggested strategies include teaching, then re-teaching; getting the child to explain things back in his own words; and requiring the use of words different from the ones used in the initial explanation. These strategies will push the child to process and hold on to the information that has been presented rather than to offer rote repetition.
Where We Stand
Whether or not nonverbal learning disability becomes accepted as a distinct condition by our own and other professions, it is an emerging diagnostic category in clinical practice. Although we do not yet have conclusive empirical evidence to substantiate clinical accounts of language and communication problems, it appears that these children have substantial difficulties with semantics and pragmatics of language. I have suggested that Bishop's Children's Communication Checklist be added to standard assessment batteries when the child is suspected of pragmatic language impairment. Until we have data that pinpoint whether or how the language deficits associated with the NLD phenomenon are distinct from semantic-pragmatic disorder or pragmatic language impairment, it seems appropriate to manage these children as if they belonged to that group.
A short article such as this one can never provide SLPs with all the information that they "need to know." Indeed, it's clear that much of what we need to know remains to be discovered. Still, this article represents a summary of what we know and hopefully prepares the practicing SLP for receiving new information as the research becomes available.