The neural basis of developmental dyslexia

Until recently, many thought developmental dyslexia was a behavioral disorder that primarily affected reading. In fact, it is a partly heritable condition, the clinical manifestations of which are extremely complex including deficits in reading, working memory, sensorimotor coordination, and early sensory processing. Even though extensive research has characterized these behavioral abnormalities carefully, the biological mechanisms of the clinical manifestations still are poorly understood. Recent research into both the nature of the structural and functional abnormalities in developmental dyslexia and the functional neuroanatomy of reading have rapidly advanced our understanding of the localization of the processes responsible for the signs and symptoms of dyslexia. This paper reviews recent evidence supporting a biological basis for developmental dyslexia. This article was made possible by grant NICHD HD36461 from The Charles A. Dana Foundation and The International Dyslexia Association.     

Cerebral dominance and subtypes of developmental dyslexia

Conclusions Evidence of different syndromes of developmental dyslexia raises the question of the interaction between dyslexic types and patterns of cerebral dominance. Some of the proposed classifications of dyslexia, and most notably the one proposed by Boder (1971), strongly suggest that dyslexic subtypes, that can be identified clinically by reading-spelling patterns, may possess different or opposite cerebral dominance patterns. Thus, research of cerebral dominance in dyslexia (i.e., Orton’s hypothesis) should involve careful selection and classification of subjects. When this is done it can be shown that electrophysiological measures can identify cerebral-dominance abnormalities in at least one subtype of developmental dyslexia. This paper was presented in part at the 29th Annual Conference of The Orton Society, November 1978, in Minneapolis, Minnesota.     

Are there radiological changes in the brains of individuals with dyslexia?

Summary CT scans of a group of patients with developmental dyslexia have shown statistically a difference of mass distribution in the cerebral hemispheres from that seen in control patients studied during the same period. They have also shown an increased incidence of unusual ventricular asymmetries from that commonly occurring in normal individuals. The findings suggest there may be an increased incidence of early slight morphological changes in the brains of individuals with dyslexia but the changes are not diagnostic of dyslexia.     

Dyslexia heterogeneity: cognitive profiling of Portuguese children with dyslexia

Recent studies have emphasized that developmental dyslexia is a multiple-deficit disorder, in contrast to the traditional single-deficit view. In this context, cognitive profiling of children with dyslexia may be a relevant contribution to this unresolved discussion. The aim of this study was to profile 36 Portuguese children with dyslexia from the 2nd to 5th grade. Hierarchical cluster analysis was used to group participants according to their phonological awareness, rapid automatized naming, verbal short-term memory, vocabulary, and nonverbal intelligence abilities. The results suggested a two-cluster solution: a group with poorer performance on phoneme deletion and rapid automatized naming compared with the remaining variables (Cluster 1) and a group characterized by underperforming on the variables most related to phonological processing (phoneme deletion and digit span), but not on rapid automatized naming (Cluster 2). Overall, the results seem more consistent with a hybrid perspective, such as that proposed by Pennington and colleagues (2012), for understanding the heterogeneity of dyslexia. The importance of characterizing the profiles of individuals with dyslexia becomes clear within the context of constructing remediation programs that are specifically targeted and are more effective in terms of intervention outcome.     

Developing an ambivalence perspective on medical labelling in education: case dyslexia

There are several social actors involved in the process of constructing the social meaning of dyslexia—namely, parents, teachers, educational authorities and organisations representing dyslectics. Some of these actors emphasise the constructive social powers related to the dyslexia label, while others perceive dyslexia as diagnostic reasoning counter productive to the learning processes. In the discussion of this paradox, this article uses sociological medicalisation theory as a provider of perspectives on medical labelling as contested, and on how the labelling process is socially structured. Empirically, the article is based on four studies in Scandinavia of the construction of dyslexia in different social settings, such as individual life stories, parent stories, educational politics and the legal system. The medicalisation perspective is found most useful for the understanding of undesirable effects. To understand reported experience of medical labelling as empowering, other sociological perspectives are more useful.     

Planum temporale asymmetry: In-vivo morphometry affords a new perspective for neuro-behavioral research

High-resolution magnetic resonance (MR) imaging today allows the in vivo quantification of the surface area of the cortex covering the planum temporale and permits assessment of the direction and degree of individual left-right asymmetry of this structure. This methodologic advance is promoting new studies on the biological mechanisms of anatomic and functional lateralization and on the structural accompaniments of disorders such as developmental dyslexia. It is important to stress that studies must agree on the definition and measurement of planum asymmetry, and we review our definition and its justification in the present article.Data obtained from normal subjects supported the assumption that planum (a)symmetry underlies functional lateralization. Thus, familial sinistrality predicted for symmetry of the planum in all eight left-handers studied. The pattern of planum symmetry in the normals was similar to that found in the post mortem studies of dyslexic individuals. Insofar as hand preference and developmental dyslexia are in part genetically transmitted, we suggest that planum symmetry may represent an inherited condition as well. Further-more, even though planum symmetry is part of the anatomic substrate of developmental dyslexia, it is unlikely that it represents a form of developmental anatomic pathology.     

The double-deficit hypothesis: a comprehensive analysis of the evidence

The double-deficit hypothesis of developmental dyslexia proposes that deficits in phonological processing and naming speed represent independent sources of dysfunction in dyslexia. The present article is a review of the evidence for the double-deficit hypothesis, including a discussion of recent findings related to the hypothesis. Studies in this area have been characterized by variability in methodology--how dyslexia is defined and identified, and how dyslexia subtypes are classified. Such variability sets limitations on the extent to which conclusions may be drawn with respect to the double-deficit hypothesis. Furthermore, the literature is complicated by the persistent finding that measures of phonological processing and naming speed are significantly correlated, resulting in a statistical artifact that makes it difficult to disentangle the influence of naming speed from that of phonological processing. Longitudinal and intervention studies of the double-deficit hypothesis are needed to accumulate evidence that investigates a naming speed deficit that is independent of a phonological deficit for readers with dyslexia. The existing evidence does not support a persistent core deficit in naming speed for readers with dyslexia.     

发展性阅读障碍的神经机制及其对第二语言学习的影响

研究表明拼音文字系统的发展性阅读障碍者与以中文为代表的表意文字系统的发展性阅读障碍者在阅读过程中大脑的激活部位存在差异。关于母语阅读障碍儿童对第二语言学习的影响是近年来发展性阅读障碍研究的热点。双语发展性阅读障碍的理论假设主要有两种语言相互依赖假设和正字法依赖假设。前者认为母语的阅读障碍可以自动迁移到第二语言的学习中;后者认为母语的阅读障碍是否会迁移到第二语言的学习中,要依赖两种语言的正字法特征。我们认为这两种理论不是相互矛盾的,阅读障碍是否会同时出现在两种语言中可能取决于这两种语言是否共用了相同的有缺陷的神经系统。     

Tennessee meets the challenge of dyslexia

In 1993, the Tennessee General Assembly voted funds to establish a model unit of integrated services and research to address the full scope of issues associated with dyslexia. Dyslexia is characterized as significant difficulty in reading and spelling individual words. In the Tennessee Center for the Study and Treatment of Dyslexia, these problems are presumed to be the consequence of a phonological core deficit. When compared to typical readers, matched for age or reading level, dyslexic readers evidence average listening comprehension, a relative strength in reading comprehension, deficits in word recognition and spelling, and severe deficits in word analysis as well as in awareness and manipulation of phonemes. Integration of this information yields a diagnostic profile that may be applied in the differential diagnosis of dyslexia both in clinical and school settings. This paper presents an overview of the Tennessee Center for Dyslexia and the services it provides as well as its guidelines for interpreting the results of norm-referenced tests and criterion-referenced measures to diagnose dyslexia and plan appropriate intervention. Frith’s (1985, 1986) developmental framework for reading acquisition is integrated with the assessment data to outline an instructional plan that addresses mastery of skills within and across the hierarchical phases—logographic, alphabetic, and orthographic—of reading development.     

Coherent motion sensitivity and reading development in the transition from prereading to reading stage

Evidence suggests that sensitivity to coherent motion (CM) is related to reading, but its role in the etiology of developmental dyslexia remains unclear. In this longitudinal study, CM sensitivity was measured in 31 children at family risk for dyslexia and 31 low-risk controls. Children, diagnosed with dyslexia in third grade (mean age=8 years 3 months), demonstrated reduced CM sensitivity in kindergarten (mean age=5 years 8 months), before they had learned to read. Preschool CM thresholds in controls also uniquely predicted future literacy achievement. When reassessed in first grade, CM sensitivity in the dyslexic children was age appropriate, and CM thresholds in the controls no longer predicted literacy acquisition. These findings contribute to the debate about the developmental relations between visual processing and reading acquisition.     

Orthographic processing efficiency in developmental dyslexia: an investigation of age and treatment factors at the sublexical level

Reading fluency beyond decoding is a limitation to many children with developmental reading disorders. In the interest of remediating dysfluency, contributing factors need to be explored and understood in a developmental framework. The focus of this study is orthographic processing in developmental dyslexia, and how it may contribute to reading fluency. We investigated orthographic processing speed and accuracy by children identified with dyslexia that were enrolled in an intensive, fluency-based intervention using a timed visual search task as a tool to measure orthographic recognition. Results indicate both age and treatment effects, and delineate a link between rapid letter naming and efficient orthographic recognition. Orthographic efficiency was related to reading speed for passages, but not spelling performance. The role of orthographic learning in reading fluency and remediation is discussed.     

发展性阅读障碍眼动研究的进展

发展性阅读障碍一直是心理学家关注的重要领域。国外研究者基于认知和生物因素提出了关于发展性阅读障碍的语音缺陷、小脑缺陷、一般性大细胞功能障碍等理论,并考察了患者的眼动特征,提出了有效的诊治方法。汉语发展性阅读障碍研究主要局限在语音和正字法领域,也涉及局部脑区的功能缺陷,但还未从多角度测查其成因,如眼动。该文在理论梳理的基础上,系统探讨了发展性阅读障碍患者的眼动特征及机制。     

Genetics and Neuroscience in Dyslexia: Perspectives for Education and Remediation

ABSTRACT— Our understanding of the causes of a developmental disorder like dyslexia has received recent input from both neuroscience and genetics. The discovery of 4 candidate genes for dyslexia and the identification of neuronal networks engaged when children read and spell are the basis for introducing this knowledge into education. However, the input from educational practitioners as well as empirical knowledge from research on learning also contribute significantly to our understanding of how children acquire the basic skills for learning to read and spell. It is imperative to merge the knowledge acquired from research in the fields of neuroscience, genetics, and empirical education, as well as to understand how the learning brain and instruction interact. Doing so can be seen as a major step in attaining an optimal approach for teaching, reading, and spelling and for finding the best suited and most effective treatment concepts for dyslexic children and adolescents.     

Understanding the ‘Lexia’ in dyslexia: A multidisciplinary team approach to learning disabilities

The historical roots of the IQ-achievement discrepancy definition of learning disability are discussed as a reference point for explaining why this definition came into being and why it is inadequate for dealing with the variety of learning and developmental disabilities that present in school settings. A proposal is offered and justified for defining learning disabilities on the basis of profiles for multiple developmental domains that affect learning. In this proposal, developmental dyslexia is differentiated from other learning disabilities. Developmental dyslexia is defined as uneven development (dissociation) between word reading and higher-level processes in the functional reading system. Dyslexics may struggle with word reading because of deficits in phonological processes, orthographic-phonological connections, and/or fluency (rate, automaticity, or executive coordination). The need for both national and international classification schemes for defining specific learning and developmental disabilities for the purposes of educational services and research is emphasized. Grant P50 33812-06 from the National Institute of Child Health and Human Development supported preparation of this article.     

Practitioners’ perceptions of dyslexia and approaches towards teaching learners with dyslexia in adult literacy classes

Learners with dyslexia are likely to be over-represented in adult literacy classes because of the convergence in perceptions, causes and understanding of literacy problems and dyslexia. Given the great amount of apprehension about practitioners’ and policy makers’ understanding of dyslexia itself, it is important to carry out an exploration of the perceptions of literacy teachers, who increasingly have responsibility for teaching learners with dyslexia. This study reports such an exploration. It employed a questionnaire survey and a focus group interview to collect data on the perceptions of literacy teachers on issues around the teaching of learners with dyslexia. The data collected were analysed using the conceptual analysis strand of concept analysis. It found that their perception of dyslexia and their approaches to teaching learners with dyslexia were informed by a dominant discourse which derives from a deficit model of dyslexia and which concurs with the metaphor of dyslexia and illiteracy as a form of disease. Furthermore, participants in this research revealed that they had limited confidence in the long-term value of the tuition they provide to their learners. The study concludes by highlighting that there is a need to explore alternatives in terms of perceptions and approaches if learners with dyslexia are to succeed in literacy classes.     

Auditory Processing of Amplitude Envelope Rise Time in Adults Diagnosed With Developmental Dyslexia

Studies of basic (nonspeech) auditory processing in adults thought to have developmental dyslexia have yielded a variety of data. Yet there has been little consensus regarding the explanatory value of auditory processing in accounting for reading difficulties. Recently, however, a number of studies of basic auditory processing in children with developmental dyslexia have suggested that a reduced ability to discriminate the rate of change in amplitude envelope onsets (rise time) may be linked to phonological processing difficulties and thereby to reading difficulties. Here, we select a range of different rise-time tasks used with children, and give them to adults with developmental dyslexia, along with 2 other auditory tasks (intensity discrimination and temporal order judgment). Deficits in both rise-time perception and temporal order judgment were found to predict literacy attainment in adults with developmental dyslexia, but the data were suggestive of different causal pathways.     

Developmental dyslexia,cerebellar/vestibular brain function and possible links to exercise-based interventions: a review

The Phonological Processing Deficit (PPD) hypothesis remains the most influential theory to explain why some children fail to acquire appropriate reading skills. However, current research suggests that there may be other deficits operating, and that the phonological processing deficit may be just one manifestation of a deeper underlying anatomical syndrome that originates in the cerebellar or vestibular areas of the brain. Claims that exercise regimes or programmes of vestibular stimulation may provide a ‘cure’ for developmental dyslexia (specific reading difficulties) prompt scepticism among the scientific community and raise concerns about the exploitation of vulnerable parents. The paper provides a review of research into the causes of specific reading difficulties at the behavioural, cognitive and biological level of explanation, and considers whether or not there is any theoretical basis for the use of exercise-based intervention programmes. Following consideration of recent findings from a range of scientific disciplines, it is concluded that such ‘unconventional’ methods of intervention may draw some theoretical support from the scientific literature, although researchers are cautioned to be wary of comorbidity issues. It is also concluded that more rigorous and independent evaluations of the success (or otherwise) of exercise-based interventions are needed.     

发展性阅读障碍者的注意转换缺陷研究综述

发展性阅读障碍者的注意转换缺陷近十年来广受研究者关注.研究者发现阅读障碍者在注意转换上表现出时间延迟,并且时间延迟同时存在于多通道;阅读障碍者在注意转换的空间特点上表现出"左视野忽视"的左右空间加工不对称现象;阅读障碍者的注意转换时空缺损影响其词汇加工和阅读.在对阅读障碍者注意转换的未来研究中,应当排除无关变量对结果的干扰,同时控制被试选取、研究工具等,进一步明确注意转换缺损与阅读障碍者言语加工的关系.     

Auditory processing interventions and developmental dyslexia: a comparison of phonemic and rhythmic approaches

The purpose of this study was to compare the efficacy of two auditory processing interventions for developmental dyslexia, one based on rhythm and one based on phonetic training. Thirty-three children with dyslexia participated and were assigned to one of three groups (a) a novel rhythmic processing intervention designed to highlight auditory rhythmic information in non-speech and speech stimuli; (b) a commercially-available phoneme discrimination intervention; and (c) a no-intervention control. The intervention lasted for 6 weeks. Both interventions yielded equivalent and significant gains on measures of phonological awareness (at both rhyme and phoneme levels), with large effect sizes at the phoneme level. Both programs had medium effect sizes on literacy outcome measures, although gains were non-significant when compared to the controls. The data suggest that rhythmic training has an important role to play in developing the phonological skills that are critical for efficient literacy acquisition. It is suggested that combining both prosodic/rhythmic and phonemic cues in auditory training programs may offer advantages for children with developmental dyslexia. This may be especially true for those who appear resistant to conventional phonics training methods.