Introduction

Typically, arguments for the neurobiological basis of reading disability/dyslexia are drawn from two large bodies of research – one on the brain and the other on the genome. This chapter first presents a discussion of the literature on the so-called reading brain – the brain as it is engaged in reading and reading-related processes (Wolf, 2007). After this, it turns to the genome, as variability in its structure and function is thought to form the substrate, through the brain and, perhaps, other organs of the human organism (e.g., the liver by means of metabolizing Omega 3 fish oil, as discussed in Lindmark & Clough, 2007), of the neurobiological foundation of reading.

This chapter necessarily makes reference to many technical terms (e.g., specific regions of the brain, biological processes) that are likely to be unfamiliar to the nonspecialist. In order to conform to space restrictions and to maintain narrative coherence and flow, descriptions and definitions of many of these have not been provided. Helpful information about these terms should be readily available both from Internet sources and publications referenced in this chapter.

Introduction

This chapter examines the evidence concerning the nature and role of a number of cognitive processes that have been proposed as influential in dyslexia/reading disability (i.e., phonological awareness, rapid naming, short-term/working memory, low-level sensory auditory and visual processing, scotopic sensitivity, attentional factors, and motor processing). In each case the implications of the available research evidence for clinical and educational intervention will be considered. As this chapter demonstrates, this highly complex field is rendered additionally problematic by often contrasting and inconsistent research findings that have resulted in much debate and little consensus, beyond wide-spread agreement that reading disability appears to be explained by multiple deficits.

The phonological deficit hypothesis

For most of the past four decades, the phonological deficit hypothesis (Stanovich, 1988; Stanovich & Siegel, 1994) has been the dominant cognitive explanation (Vellutino et al., 2004). Studies of cognitive functioning in children with reading problems have consistently found three processes – phonological processing, short-term/working memory, and processing speed – that appear particularly significant when comparisons are made with typically achieving readers (Johnson et al., 2010). For each of these processes there appears to be a phonological component that is particularly important for reading. According to some theorists, the phonological deficit incorporates elements that map onto these three major dimensions: phonological awareness, verbal short-term memory, and slow retrieval of phonological information stored in long-term memory, as exemplified in rapid automatic naming tasks (Wagner & Torgesen, 1987). However, this grouping is controversial, and others argue that it is not helpful to conceive of verbal short-term/working memory and naming speed as core elements of phonology (Nicolson & Fawcett, 2008).

The debate about how we should understand the concept of developmental dyslexia has sometimes become oversimplified to the point that the very existence of a biologically based reading disability has been questioned. Such a position is untenable, yet it is not always understood that criticism of the scientific rigor of a given label or construct does not necessarily imply that the problems it seeks to encompass are not real or meaningful. Thus, critical concerns expressed about the value of the dyslexia construct have been incorrectly understood or reframed by some as reflecting a perception that the term serves as an “excuse” for laziness, stupidity, or poor teaching. While there remain some commentators who certainly hold such views, the great majority of critiques in the academic literature (Elliott & Gibbs, 2008; Soler, 2010; Stanovich, 1994) have sought to provide a more nuanced perspective that eschews such notions.

In 2005, the dyslexia debate gained prominence in many countries as a result of widespread coverage given to a British television program, The Dyslexia Myth (http://topdocumentaryfilms.com/dyslexia-myth/). The main assertion of this program was that there were many myths surrounding the nature of dyslexia and its treatment. Existing practice, where only a limited proportion of struggling readers were identified as having dyslexia, typically on the basis of extensive cognitive assessments, was resulting in delays in intervention for some and no intervention for other candidates who also needed help. The program's message, largely reflecting the perspective of the response to intervention movement, was misperceived by some as stating that biologically based reading difficulties were a myth (see, for example, Nicolson [2005] and a subsequent response to this by Elliott [2005]). Surprisingly, this perception flew in the face of clear statements to the contrary that were offered throughout the program. What was actually being questioned were the rigor, utility, and added value of a clinical diagnosis of dyslexia, not the existence of the very real underlying problems that those with complex reading difficulties typically encounter. Rather than focusing on expensive assessments, often more accessible to children from socioeconomically advantaged families (Sternberg & Grigorenko, 1999b), and usually undertaken after long-term failure had been established, it was recommended that intervention should be conducted as early as possible with all those who were potentially at risk of reading difficulty, irrespective of etiology.