Is a cerebellar deficit the underlying cause of reading disabilities?

This study investigated whether children with dyslexia differed in their performance on reading, phonological, rapid naming, motor, and cerebellar-related tasks and automaticity measures compared to reading age (RA)-matched and chronological age (CA)-matched control groups. Participants were 51 children attending mainstream English elementary schools in Quebec. All participants completed measures of IQ, word and nonword reading fluency, elision, nonword decoding, rapid naming, bead threading, peg moving, toe tapping, postural stability, and muscle tone. Results from both group contrasts and analyses at the individual case level did not provide support for claims of motor–cerebellar involvement in either typical or atypical reading acquisition. Results were more consistent with a phonological core process account of both typical reading and reading difficulty. Phonological deficits for children with dyslexia compared to RA-matched controls were, however, only evident in group contrasts. Findings thus also have important implications for identifying at-risk readers among their same-aged peers.     

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.     

Naming speed in dyslexia and dyscalculia

In four carefully selected samples of 8- to 10-year old children with dyslexia (but age adequate arithmetic skills), dyscalculia (but age adequate reading skills), dyslexia/dyscalculia and controls a domain-general deficit in rapid automatized naming (RAN) was found for both dyslexia groups. Dyscalculic children exhibited a domain-specific deficit in rapid naming of quantities. This finding is in line with recent assumptions that dyscalculia is associated with a neurobiological deficit in the processing of numerosities. In the dyslexia/dyscalculia group, RAN deficits were additive, that is, the dyslexia/dyscalculia group exhibited the sum of the deficits found in the dyslexia only and dyscalculia only groups. This finding suggests that the cognitive bases of dyslexia and dyscalculia are independent from each other. Within the naming speed paradigm no differential impact of special demands on the executive functions inhibition and shifting was found for any of the four groups.     

Developmental dyslexia: Related to specific or general deficits?

The present study was designed to examine the question of whether developmental dyslexia in 12-year-old students at the beginning of secondary education in the Netherlands is confined to problems in the domain of reading and spelling or also is related to difficulties in other areas. In particular, hypotheses derived from theories on phonological processing, rapid automatized naming, working memory, and automatization of skills were tested. To overcome the definition and selection problems of many previous studies, we included in our study all students in the first year of secondary special education in a Dutch school district. Participants were classified as either dyslexic, garden-variety, or hyperlexic poor readers, according to the degree of discrepancy between their word recognition and listening comprehension scores. In addition, groups of normal readers were formed, matching the poor readers in either reading age or chronological age. A large test battery was administered to each student, including phonological, naming, working memory, speed of processing, and motor tests. The findings indicate that dyslexia is associated with deficits in (1) phonological recoding, word recognition (both in their native Dutch and in English as a second language), and spelling skills; and (2) naming speed for letters and digits. Dyslexia was not associated with deficits in other areas. The results suggest that developmental dyslexia, at the age of 12, might be (or might have become) a difficulty rather isolated from deficiencies in other cognitive and motor skills.     

Cognitive Endophenotypes of Dyslexia

The study investigated cognitive deficits associated with dyslexia and familial risk of dyslexia (endophenotypes) by comparing children from families with and without a history of dyslexia. Eighty-eight school-aged children were assessed on measures of phonology, language and rapid automatized naming. A series of regression analyses with family risk and dyslexia status as predictors indicated that word recall, morphology, and rapid automatized naming were associated with the deficit, whereas the two phonological measures (phoneme awareness and nonword repetition) were associated with both literacy deficits and family risk, suggesting that the phonological deficit is an endophenotype of dyslexia. Whereas the association with familial risk was similar for the two phonological measures, they differed in their relation to dyslexia status: Phoneme awareness showed a stronger association with dyslexia than risk status, whereas nonword repetition was more strongly related to the risk. The data are interpreted within the framework of multiple deficit models of dyslexia.     

Viewing a phonological deficit within a multifactorial model of dyslexia

Participants were administered multiple measures of phonological awareness, oral language, and rapid automatized naming at the beginning of kindergarten and multiple measures of word reading at the end of second grade. A structural equation model was fit to the data and latent scores were used to identify children with a deficit in phonological awareness alone or in combination with other kindergarten deficits. Children with a deficit in phonological awareness in kindergarten were found to be five times more likely to have dyslexia in second grade than children without such a deficit. This risk ratio substantially increased with the addition of deficits in both oral language and rapid naming. Whereas children with one or more kindergarten deficits were at heighten risk for dyslexia, some of these children were found to be adequate or better readers. These results are discussed within a multifactorial model of dyslexia that includes both risk and protective factors.     

Visual and language processing deficits in compensated and uncompensated college students with dyslexia

In seven experiments, we investigated whether compensated and uncompensated adults with dyslexia show different patterns of deficits in magnocellular visual processing and in language processing tasks. In four visual tasks, we failed to find evidence of magnocellular deficits in either group. However, both groups of adults with dyslexia showed deficits in component language skills, and the degree of reading impairment predicted the nature and extent of these deficits. Uncompensated readers showed deficits in orthographic and especially phonological coding and awareness and were slower on rapid naming. Compensated readers showed word and nonword performance below controls but better than the uncompensated readers. The compensated group was not significantly less accurate than controls on phonological awareness, nor significantly worse overall on rapid naming.     

Naming difficulties in children with dyslexia: application of the tip-of-the-tongue paradigm

The present study used the tip-of-the-tongue (TOT) experimental paradigm in a picture naming task to explore the source of the naming deficits of children with dyslexia. Compared with a control group of typically developing readers, the children with dyslexia showed fewer correct responses and spontaneous recalls, more don't know (DK) and TOT responses, and less accurate feeling of knowing (FOK) judgments. When they failed to retrieve a target word, the children with dyslexia did not differ from the control group in the partial semantic information they provided, but they gave less valid and more invalid partial phonological information. The children with dyslexia also benefited less from phonological cues. The phonologically related responses of the children with dyslexia elicited during the administration of the TOT procedure were related to their performance on a phonological awareness test. These findings suggest that the naming problems of children with dyslexia arise because of their difficulty in accessing the phonological word forms after the corresponding abstract lexical representation has been successfully accessed. The results are discussed in relation to the claim that two-stage models of naming can be profitably used in the early identification and treatment of reading disabilities.     

Cognitive-linguistic profiles of Chinese typical-functioning adolescent dyslexics and high-functioning dyslexics

Dyslexia is a developmental disability affecting the acquisition of reading and writing skills, and its developmental nature makes longitudinal research of great importance. This study therefore investigated the cognitive-linguistic profiles of the typical-functioning dyslexics and high-functioning dyslexics with longitudinal cohorts of Chinese-speaking adolescents diagnosed with childhood dyslexia. These two dyslexic groups of fifty students (with 25 typical-functioning dyslexics) were assessed in Grade 2 (Time 1) and in Grade 8 (Time 2), whereas 25 typically developing controls were assessed at Time 2. Students were administered measures of phonological awareness, morphological skills, visual-orthographic knowledge, rapid naming, verbal working memory, and literacy skills. Results showed that, at Time 2, both dyslexic groups performed less well than the control group on most of the measures. Deficits in rapid naming were particularly salient in both dyslexic groups. Comparing the two dyslexic groups, the typical-functioning dyslexics had more multiple deficits than the high-functioning dyslexics. Findings highlight the importance of rapid naming deficits as potential universal causes of dyslexia and the utility of targeting visual-orthographic knowledge and morphological skills in supporting the development of dyslexic adolescents.     

Protective Factors and Compensation in Resolving Dyslexia

ABSTRACT

Two explanations for resolving dyslexia were investigated, one assuming resolving underlying deficits and another assuming compensatory mechanisms based on cognitive strengths. Thirty-six Dutch gifted secondary-school students with either persistent (n = 18) or resolving (n = 18) dyslexia participated. Groups, matched on IQ, were assessed on dyslexia- and intelligence-related cognitive risk and protective factors. Findings for the risk factors showed support for both the resolving-deficit and compensatory-mechanism theories: Resolving and persistent groups were comparable on phoneme deletion and nonalphanumeric rapid automatized naming, but resolvers outperformed students with persistent dyslexia on spoonerisms and alphanumeric rapid automatized naming. For the protective factors, resolvers consistently showed more pronounced cognitive strengths in verbal areas relevant for literacy development, which is in line with the compensatory-mechanism theory. We conclude that, besides underlying deficits resolving to some extent, compensation is a plausible explanation for resolving literacy difficulties in gifted students.     

Naming speed deficits in adults with reading disabilities: a test of the double-deficit hypothesis

The present study investigated the persistent nature of naming speed deficits within the context of the double-deficit hypothesis in a university sample of adults with reading disabilities (RD). Twenty-five university students with RD were compared to 28 typically achieving readers on measures of reading skill, phonological processing, and naming speed. The results indicated that both naming speed and phonological processing deficits characterized the RD group. In a regression analysis, neither naming speed nor phonological processing were important variables in explaining comprehension when reading rate was in the model. The results of the present study are mixed at best and are consistent with earlier conclusions that support for the double-deficit hypothesis of dyslexia remains limited.     

Testing the double-deficit hypothesis in an adult sample

The double-deficit hypothesis of dyslexia posits that reading deficits are more severe in individuals with weaknesses in phonological awareness and rapid naming than in individuals with deficits in only one of these reading composite skills. In this study, the hypothesis was tested in an adult sample as a model of reading achievement. Participants were parents of children referred for evaluation of reading difficulties. Approximately half of all participants reported difficulty learning to read in childhood and a small subset demonstrated ongoing weaknesses in reading. Structural equation modeling results suggest that the double-deficit hypothesis is an accurate model for understanding adult reading achievement. Better reading achievement was associated with better phonological awareness and faster rapid automatized naming in adults. Posthoc analyses indicated that individuals with double deficits had significantly lower reading achievement than individuals with single deficits or no deficits.     

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.     

Automaticity, retrieval processes, and reading: a longitudinal study in average and impaired readers

In this longitudinal investigation, the development of word-retrieval speed and its relationship to reading was studied in 72 average and 11 severely impaired readers in the kindergarten to grade 2 period (5-8 years). Subjects received a battery of 3 reading measures and 4 continuous naming tests with varied stimulus requirements. Results indicated that the relationship of retrieval speed to reading is a function of development and the correspondence between higher- and lower-level processes in the specific retrieval and reading measures. As automaticity in retrieval developed in average readers, naming-speed/reading relationships moved from strong, general predictions to highly differentiated ones. The strongest correlations were between naming speed for graphological stimuli and lower-level reading tasks. Impaired readers performed slower than average readers on all naming measures across all years, particularly on graphological symbols. 3 dyslexic subgroups emerged: the largest was globally impaired across all naming rate and reading tasks; 2 smaller subgroups had early specific, retrieval-rate deficits and dissociated reading deficits.     

Comparison of deficits in cognitive and motor skills among children with dyslexia

There is a growing body of evidence that children with dyslexia have problems not just in reading but in a range of skills including several unrelated to reading. In an attempt to compare the severity and incidence of deficits across these varied domains, children with dyslexia (mean ages 8, 12, and 16 years), and control groups of normally achieving children matched for IQ and for age or reading age, were tested on a range of primitive (basic) skills. The children with dyslexia performed significantly worse than the same-age controls on most tasks, and significantly worse even than the reading-age controls on phoneme segmentation, picture naming speed, word tachistoscopic word recognition, speeded bead threading and some balance tasks. The overall performance of the children with dyslexia is interpreted as showing less complete automatization than normal.     

A Meta-Analytic Review of Naming-Speed Deficits in Developmental Dyslexia

ABSTRACT

This study presents a meta-analytic review of serial rapid automatized naming (RAN) deficits in individuals with dyslexia relative to typical readers (based on 216 effect sizes comprising 8335 dyslexic readers, 14,083 age-matched controls, and 921 reading-matched controls). A random-effects model analysis indicated a large impairment in speeded RAN in individuals with dyslexia compared with age-matched controls (d = 1.19) but a similar performance when compared with reading-matched controls (d = 0.13). In addition, dyslexic readers presented a deficit in discrete-naming formats (d = 0.74), although the deficit in serial RAN was notably larger; hence, adding seriality is particularly detrimental for these readers. The deficit appears to span all stimulus types (alphanumeric and nonalphanumeric), indicating that processes beyond letter processing are responsible for the delays and are independent of set size. Poor RAN is a long-term and universal symptom of dyslexia, and the transparency of the writing system does not influence its severity.     

阅读困难诊断标准与模式的“后智力—成就差异”趋势

阅读困难是学习困难研究中最受关注的一个领域,对整个学习困难研究领域具有重要影响。对阅读困难的有效诊断是阅读困难的研究和干预的基础。在阅读困难的诊断中,曾经广泛应用的智力—成就差异标准与模式在有效性、敏感性以及对干预的指导意义等方面存在严重不足,受到越来越多研究者和实践者的屏弃。目前,核心技能缺陷和干预—应答两类诊断标准和模式日益受到关注和采纳。我国迄今较少系统研究阅读困难的诊断标准与模式,不过,有关汉语阅读困难的初步研究鉴别出语音缺陷、快速命名缺陷和语素技能缺陷,为发展和应用核心技能标准和模式提供了重要基础,也为建立干预—应答模式提供了参考。确立汉语阅读困难诊断的核心技能与干预—应答标准与模式还有待系统和深入的研究。     

Picture naming and developmental reading disorders

One of the most frequently cited papers from the twenty‐five years of the Journal of Research in Reading is ‘Object‐naming deficits in developmental dyslexia’ by Maggie Snowling, Bente van Wagtendonk and Carolyn Stafford, published in 1988. Looking back at the paper some sixteen years after its publication, it is striking to note how topical some of the issues discussed by Snowling and colleagues remain. This commentary revisits some of these issues and examines how subsequent research has consolidated and extended Snowling et al.'s findings and conclusions.     

Are RAN deficits in university students with dyslexia due to defective lexical access,impaired anchoring,or slow articulation?

The purpose of this study was to examine different hypotheses in relation to RAN deficits in dyslexia. Thirty university students with dyslexia and 32 chronological-age controls were assessed on RAN Digits and Colors as well as on two versions of RAN Letters and Objects (one with five items repeated 16 times and one with 20 items repeated four times). In addition, participants were tested on discrete letter and object naming, phonological awareness, orthographic knowledge, and speed of processing, and the RAN Letters and Objects total times were partitioned into pause times and articulation times. Results showed first that the dyslexia group was slower than the control group on all RAN tasks and the differences remained significant after controlling for discrete naming time. Second, both groups were slower in the large item set condition (20 ×?4) than in the small set condition (5 ×?16). Third, the dyslexia group was slower than the control group in both the pause and the articulation times. Although none of the processing skills was sufficient on its own to eliminate group differences in RAN Letters components, phonological awareness, and orthographic processing were sufficient on their own to eliminate group differences in the RAN Objects pause time. Taken together, our findings suggest that the deficits in RAN are not due to impaired anchoring, but rather due to subtle impairments in lexical access (specific to alphanumeric RAN), serial processing, and articulation.     

Classification of Double Deficit Groups Across Time: An Analysis of Group Stability From Kindergarten to Second Grade

The Double Deficit Hypothesis of dyslexia is one approach to classifying students with reading disabilities. The theory offers four distinct groups of readers: (a) average readers, (b) students with phonological deficits, (c) students with naming speed deficits, and (d) students with double deficits: those having both (b) and (c). This study examines the stability of these groups from kindergarten to second grade. An initial sample of 214 students were tested at four time points on measures of rapid automatized naming, phonological awareness, and reading. Latent transition analyses were used to examine the stability of these groups over time. These analyses indicated moderate stability from kindergarten to second grade with the probability of movement between groups being higher in kindergarten and early first grade. The groups differed in reading achievement at each testing time, with the double deficit group obtaining the lowest scores. Implications for early assessment and intervention are discussed.