Several studies have provided evidence for a phonological deficit in developmental dyslexia. However, recent studies provide evidence for a multimodal temporal processing deficit in dyslexia. In fact, dyslexics show both auditory and visual abnormalities, which could result from a more general problem in the perceptual selection of stimuli. Here we report the results of a behavioral study showing that children with dyslexia have both auditory and visual deficits in the automatic orienting of spatial attention. These findings suggest that a deficit of selective spatial attention may distort the development of phonological and orthographic representations that is essential for learning to read.

This is a research review. It was undertaken to establish the evidence base for developmental dyslexia in adults. It began by searching electronic data bases, exploring library holdings, and following citation trails. This process identified a large number of potentially relevant book chapters and papers published in peer-reviewed journals, which were then read critically.

The review draws attention to a range of methodological and interpretational problems in the literature, with particular respect to sampling and research design. It presents a detailed account of phonological awareness. Four explanatory theories of dyslexia are summarised and their implications for teaching practice are assessed. Three alternative perspectives on developmental reading difficulties are described. The language in these accounts reflects, where necessary, the terminology used in their sources.

Findings :

• There are many reasons why people find it difficult to learn how to read, write and spell. Some causes of reading difficulty are located within society and some are located within the individual.
• There are many definitions of dyslexia but no consensus. Some definitions are purely descriptive, while others embody causal theories. It appears that ‘dyslexia’ is not one thing but many, in so far as it serves as a conceptual clearing-house for a number of reading skills deficits and difficulties, with a number of causes.
• There is no consensus, either, as to whether dyslexia can be distinguished in practice from other possible causes of adults’ literacy difficulties. Many ‘signs of dyslexia’ are no less characteristic of non-dyslexic people with reading skills deficits. In our present state of knowledge, it does not seem to be helpful for teachers to think of some literacy learners as ‘dyslexics’ and of others as ‘ordinary poor readers’.
• Learning to read in an alphabetic system helps, and is helped by, the development of phonemic awareness.
• Reading fluency is a complex process, and research is needed for this process to be better understood.
• The most inaccurate readers are not the most likely to be dyslexic, as most scientists use the term.
• Teachers of both initial reading and adult literacy need to be well-informed about language and its acquisition.
• The teacher’s aim must be to impart declarative knowledge (or knowledge that) and to ensure that the learner transforms it into procedural knowledge (or knowledge how) in order to be able to draw upon it without conscious attention.
• Reading interventions need to address both the cognitive and the emotional needs of adult students.
• Adult literacy learners need to be taught how their writing system works.
• The research does not indicate that ‘dyslexics’ and ‘ordinary poor readers’ should be taught by different methods. However, the methods promoted as specialist interventions for dyslexic people are well suited for mainstream teaching, which is how they originated.
• Good practice in this field rests almost entirely on professional judgement and common sense, rather than on evidence from evaluation studies. The review found no experimental evidence comparing the group outcomes between dyslexic adults and the wider population of adults with reading skills deficits.
• Many people who have difficulty in learning literacy skills can be helped by a curriculum that is both structured and explicit, with methods that reinforce their learning. However, a minority of learners do not respond to structured and explicit reading intervention programmes, and ways of helping them have yet to be developed.
• Students will not become proficient without repetitive practice.
• Computer-supported instruction can make repetitive practice acceptable to adult students.
• Findings from research with middle-class groups of mother-tongue speakers may create misleading expectations about the needs and abilities of learners in adult literacy classes.

Those who master reading skills successfully and those who have difficulties doing so differ in a wide range of reading-related processes. The central deficit experienced by poor readers appears to be related to phonological processing (a complex hierarchy of functions related to processing phonemes), whereas characteristics of automatization processes seem to moderate the reading outcome for people whose phonological skills are weak. (2) There are new data addressing models of dyslexia in languages other than English. The most fascinating finding is that the model implicating phonological deficit as central to dyslexia, and the lack of ability to automatize as leading to troubled reading, appears to be universal, regardless of the specific language.

However, there is an interaction effect between the characteristics of a particular language and the developmental model of dyslexia. In phonologically more difficult languages (e.g., English), the most pronounced weakness appears to occur in phonological processing, whereas in phonologically easier languages (e.g., German), the crucial role in the manifestation of dyslexia is played by the lack of the skills needed to achieve automatization. (3) There is abundant evidence that reading (i.e., any single act of reading as well as reading as a holistic process) is “cooked” by the brain. Although no unified brain map of reading has been developed, some specific areas of the brain have been implicated in different reading-related cognitive processes by different laboratories and on different samples. (4) Indisputable evidence has been accumulated suggesting the involvement of the genome in developmental dyslexia. As of now, specific regions of the genome have been identified as being intimately involved with a number of different reading-related processes.

Today the field of developmental dyslexia is the only area of genetic studies of human abilities and disabilities in which linkages to the genome have been robustly replicated in independent laboratories. (5) Finally, evidence suggests that developmental dyslexia might be only one of the manifestations of a deep, underlying, anatomical syndrome. The comorbidity of developmental dyslexia with both internalizing and externalizing behavioral disturbances, as well as with other learning disabilities, underscores the need for wide-ranging cognitive and behavioral approaches in the remediation programs offered to dyslexic children.