History, Definition, and Diagnosis of NLD
Samuel Kirk first used the term learning disabilities (Danforth, 2011; Mather & Morris, 2011) to describe disordered or delayed development of a range of academic skills in children. These skills were primarily reading, but also included mathematics, writing (handwriting and written expression), oral expression, and spelling (Kirk & Bateman, 1962). Johnson and Myklebust (1967) were the first to use the term nonverbal learning disabilities (NLD), or learning problems that occurred at the perceptual level of experience. Myklebust (1975) further described the characteristics of NLD as self-imperception, including a lack of recognition of parts of one’s own body and the spatial relationships between them; social imperception and facial agnosia, or an impairment in recognizing faces; difficulties understanding visual and spatial concepts such as size, height, weight, laterality and direction; perceptual speed and motor deficits; and problems with academic and life skills such as learning to print, or to dress oneself (1975). As may be gathered from this summary, early work emphasized social and perceptual deficits over academic ones.
Academic achievement in NLD is not necessarily impaired in the first years of school, a point made by Rourke (2000) in exploring reasons for a lack of research into the disorder. Rourke and his colleagues emphasized psychosocial outcomes in their studies. They explored whether a predisposition to mental illnesses was part of a larger NLD syndrome originating in lateralized, or left versus right hemisphere, cortical differences (Rourke, 1989; 2000; see also Palombo & Feigon, 1986; Palombo, 2006). A related approach (Gross-Tsur, Shalev, Manor, & Amir, 1995; Humphries, Oram Cardy, Worling, & Peets, 2004; Worling, Humphries, & Tannock, 1999) has been to investigate functional consequences of the hypothesis that NLD is related to right hemisphere deficits. In the same tradition, the work of Cornoldi, Mammarella, and their colleagues has examined visual-spatial cognition in children with NLD (e.g., Mammarella et al., 2006; Mammarella, Giofrè, Ferrara, & Cornoldi, 2013; Venneri, Cornoldi & Garuti, 2003), and in the delineation of NLD groups for clinical and research purposes (Cornoldi, Venneri, Marconato, Molin, & Montinari, 2003; Mammarella & Cornoldi, 2014).
A separate stream of research has investigated medical syndromes with known white matter disturbances, a documented underpinning of right hemisphere impairments (e.g., Bonner, Hardy, Willard, & Gururangan, 2009; McCann et al., 2008; Ris et al., 2007; Rissman, 2011; Steele et al., 2005). Right hemisphere dysfunction is connected to a general NLD syndrome through the white matter hypothesis (Rourke, 1989; 1995). Briefly, the hypothesis is that myelin, a fatty, white substance that insulates neurons and is responsible for efficient neural communication, has been damaged. Damage results in under-connected neural circuits. The theory is based on the hypothesis that white matter volume is greater in the right hemisphere than in the left, resulting in the right hemisphere’s characterization as the hemisphere most responsible for processes that are integrative in nature (Jung-Beeman, 2005; Goldberg & Costa, 1981). Therefore, difficulties with integration, as well as with visual-spatial abilities, emotion regulation, and other right hemisphere-biased processes in typically lateralized people, are observed in NLD (Rourke, 1989; 1995). Studies reviewed in the present chapter, however, did not include the medical approach to investigating NLD. None of the participants in the study described here reported histories of co-morbid medical conditions related to NLD, in which the possibility of right hemisphere differences may have been assessed medically or exists by definition as part of the medical condition involved. The results and discussion reflect an educational approach to the topic.
NLD has not been included in any of the iterations of the Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association (APA) to guide practitioners in the diagnosis of mental illnesses and developmental disorders.1 This exclusion has resulted from a mismatch between diagnostic systems that focus on symptoms, and definitions used by researchers in evaluating other aspects of these disorders (Ris & Nortz, 2008). In the DSM, the symptoms of learning disabilities are academic skill weaknesses, rather than cognitive processes or neuropsychological impairments that underlie them. In reading disability, or dyslexia, research concerning underlying impairments has converged with the academic weakness described by the label. This has not been the case, however, with NLD. As will be explored below, there is no single academic skill that is impaired in NLD.
One consequence of NLD’s exclusion from the DSM is that it has been difficult to estimate its prevalence. Some estimates have been as high as 29% of the total population with learning disabilities, which itself may be as high as 15% of school age children (Dugbartey, 2000). A more commonly cited estimate is 5% to 10% of those who seek services or accommodation for learning disorders (Davis & Broitman, 2011). A second consequence is that research has concentrated on differentiating NLD from other disorders such as dyslexia, attention-deficit/hyperactivity disorder (ADHD), mood and anxiety disorders, and forms of autism (Antshel & Khan, 2008; Davis & Broitman, 2011; Fine, Semrud-Clikeman, Bledsoe, & Musielak, 2013). This in turn has limited empirical exploration of heterogeneity in NLD. Subtyping has been recommended (Mammarella et al., 2006; Ris & Nortz, 2008), and subtypes have been proposed (Davis & Broitman, 2011; Forrest, 2004; Grodzinsky, Forbes, & Holmes Bernstein, 2010; Mamen, 2007; Palombo, 2006), but as yet these have not been pursued empirically.
In the fifth edition of the DSM (DSM-5, APA, 2013), disorders of reading, mathematics, and written expression have been contained within a single Specific Learning Disorder diagnosis, one of seven types of Neurodevelopmental Disorder. Specifiers, or statements that further describe features of the diagnosis, reflect the original educational classifications. For this reason, it seems unlikely that this shift will alter patterns of diagnosis. Practitioners have used clinical experience, case studies, and research findings to diagnose NLD (Fine et al., 2013; Mamen, 2007; Palombo, 2006; Solodow et al., 2006; Yalof, 2006) and will continue to do so. The vast majority of research in NLD has been conducted with children, and until recently a lack of studies involving adult participants has been the rule (Casey, 2012). After reviewing current findings in children, this chapter will concentrate on adding to the sparse clinical and empirical information concerning adults with NLD. A section describing language and social perception will provide the background to three research questions investigated with a sample of these adults, for which results are subsequently reported.