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.     

Impaired performance of children with dyslexia on a range of cerebellar tasks

It is now thought that the cerebellum is involved in the acquisition of “language dexterity” in addition to its established role in motor skill acquisition and execution. Mild cerebellar impairment, therefore, provides a possible explanation of a range of problems shown by children with dyslexia. The authors have established suggestive evidence in support of this hypothesis in tests of balance and of time estimation. In a further test of the hypothesis, a battery of clinical tests for cerebellar impairment, including tests of muscle tone and of coordination, was administered to matched groups of children with dyslexia and control children aged 10, 14, and 18 years (55 subjects in all). The children with dyslexia showed highly significant impairments on all the cerebellar tests, and significant impairment compared even with reading age controls on 11 of the 14 tasks. Deficits on the majority of tests were among the largest found in our research program. The findings, therefore, provide further intriguing evidence of cerebellar impairment in dyslexia. We speculate that the well-established phonological deficits in dyslexia may arise initially from inefficient articulatory control attributable to cerebellar impairment.     

Do the effects of computer-assisted practice differ for children with reading disabilities with and without IQ-achievement discrepancy?

This study was designed to assess whether the effects of computer-assisted practice on visual word recognition differed for children with reading disabilities (RD) with or without aptitude-achievement discrepancy. A sample of 73 Spanish children with low reading performance was selected using the discrepancy method, based on a standard score comparison (i.e., the difference between IQ and achievement standard scores). The sample was classified into three groups: (1) a group of 14 children with dyslexia (age M = 103.85 months; SD = 8.45) who received computer-based reading practice; (2) a group of 31 "garden-variety" (GV) poor readers (age M = 107.06 months; SD = 6.75) who received the same type of instruction; and (3) a group of 28 children with low reading performance (age M = 103.33 months; SD = 9.04) who did not receive computer-assisted practice. Children were pre- and posttested in word recognition, reading comprehension, phonological awareness, and visual and phonological tasks. The results indicated that both computer-assisted intervention groups showed improved word recognition compared to the control group. Nevertheless, children with dyslexia had more difficulties than GV poor readers during computer-based word reading under conditions that required extensive phonological computation, because their performance was more affected by low-frequency words and long words. In conclusion, we did not find empirical evidence in favor of the IQ-achievement discrepancy definition of reading disability, because IQ did not differentially predict treatment outcomes.     

Persistence of phonological awareness deficits in older children with dyslexia

Three groups of children with dyslexia, with mean age 8, 13 and 17 years, together with three groups of normally achieving children matched for age and IQ with the dyslexic groups, undertook tests of sound categorization and phoneme deletion. The design allowed comparison not only across chronological age but also across reading age. The children with dyslexia performed significantly worse even than their reading age controls on both tasks. Indeed, overall performance of the 17 year old children with dyslexia was closest, but inferior, to that of the 8 year old controls. Since the sound categorization task was designed to minimize working memory load, the results extend previous findings on the phonological awareness deficits in dyslexia by dissociating the deficit from memory load and by showing that it persists at least into late adolescence.     

What is the Role of Intelligence in the Identification of Specific Learning Disabilities? Issues and Clarifications

A fundamental assumption in the identification of specific learning disabilities (SLD) has been that the presence of a severe discrepancy between ability and academic achievement is a valid marker for the presence of a SLD. This assumption is based on the notion that discrepant low achievers constitute a unique group of children who are different in a number of ways from nondiscrepant low achievers. Several meta‐analytic reviews contrasting discrepant and nondiscrepant low achievers fail to reveal significant differences between these two groups on measures of phonetic analysis, pseudoword decoding, word identification, spelling, oral reading fluency and other measures of literacy development and related phonological processing skills. This paper discusses the role of intelligence in identifying children with SLD and presents data based on correlational analyses and hierarchical regression analyses showing that intelligence is not a strong predictor of reading achievement and does not predict responsiveness to remedial instruction. These data also indicate that direct measures of responsiveness to intervention (RTI) strongly predict later reading achievement in tutored children from 1st grade through 4th grade. The combined results suggest that RTI approaches to the identification of SLD may have greater utility than psychometric approaches based on IQ scores or individual profile analysis.     

An evaluation of the discrepancy definition of dyslexia.

The purpose of this study was to determine whether children with dyslexia, that is, children whose reading levels were significantly lower than would be predicted by their IQ scores, constituted a distinctive group when compared with poor readers, that is, children whose reading scores were consistent with their IQ scores. The performance of children with dyslexia, poor readers, and normally achieving readers was compared on a variety of reading, spelling, phonological processing, language, and memory tasks. Although the children with dyslexia had significantly higher IQ scores than the poor readers, these two groups did not differ in their performance on reading, spelling, phonological processing, or most of the language and memory tasks. In all cases, the performance of both reading disabled groups was significantly below that of nondisabled readers. The findings were similar whether absolute difference or regression scores were used. Reading disabled children, whether or not their reading is significantly below the level predicted by their IQ scores, experience significant problems in phonological processing, short-term and working memory, and syntactic awareness. On the basis of these data, there does not seem to be a need to differentiate between individuals with dyslexia and poor readers. Both of these groups are reading disabled and have deficits in phonological processing, verbal memory, and syntactic awareness.     

Reading disability defined as a discrepancy between listening and reading comprehension: a longitudinal study of stability, gender differences, and prevalence

The purpose of this study was to determine whether defining reading disability by a discrepancy between group-administered tests of listening and reading comprehension would produce result similar in terms of stability, gender ratio, and prevalence to IQ-achievement test discrepancy definitions. The total population of a small school district (N = 1,008) was followed from prekindergarten through Grade 7-8 for 13 years. As is often seen in epidemiological studies using IQ and individually administered reading tests to define reading disability, stability in the classification of reading disability was low. Among the participants with a consistent reading disability, the male-to-female ratio was 3.2:1, compared with 1.3:1 for the 5.1% of the sample who were nondiscrepant poor readers in both lower and upper grades. A mean 2.7% of the population was classified as reading disabled over the eight-grade span, and only 1.7% demonstrated a consistent reading disability in both the lower and the upper grades. An increase in the ratio of nondiscrepant to discrepant poor readers after Grade 5 was due mainly to late-emerging poor readers. It was concluded that defining reading comprehension disability in terms of a discrepancy between listening and reading comprehension provides a fairly accurate estimate of the stability, gender ratio, and prevalence of the disorder.     

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.     

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.     

Basic auditory processing and developmental dyslexia in Chinese

The present study explores the relationship between basic auditory processing of sound rise time, frequency, duration and intensity, phonological skills (onset-rime and tone awareness, sound blending, RAN, and phonological memory) and reading disability in Chinese. A series of psychometric, literacy, phonological, auditory, and character processing tasks were given to 73 native speakers of Mandarin with an average age of 9.7 years. Twenty-six children had developmental dyslexia, 29 were chronological age-matched controls (CA controls) and 18 were reading-matched controls (RL controls). Chinese children with dyslexia were significantly poorer than CA controls in almost all phonological tasks, in semantic radical search, and in phonological recoding proficiency. Chinese children with dyslexia also showed significant impairments in most of the basic auditory processing tasks. Regression analyses demonstrated that different auditory measures of rise time discrimination were the strongest predictors of individual differences in Chinese character reading (1 Rise task) and phonological recoding (2 Rise task) respectively, with frequency discrimination also important for nonsense syllable decoding. Our results support the hypothesis that accurate perception of the amplitude envelope of speech is critical for phonological development and consequently reading acquisition across languages.     

Developmental Outcomes for Children at High Risk of Dyslexia and Children With Developmental Language Disorder

We followed children at family risk of dyslexia and children with preschool language difficulties from age 3½, comparing them with controls (N = 234). At age 8, children were classified as having dyslexia or Developmental Language Disorder (DLD) and compared at earlier time points with controls. Children with dyslexia have specific difficulties with phonology and emergent reading skills in the preschool period, whereas children with DLD, with or without dyslexia, show a wider range of impairments including significant problems with executive and motor tasks. For children with both dyslexia and DLD, difficulties with phonology are generally more severe than those observed in children with dyslexia or DLD alone. Findings confirm that poor phonology is the major cognitive risk factor for dyslexia.     

Amplitude envelope perception, phonology and prosodic sensitivity in children with developmental dyslexia

Here we explore relations between auditory perception of amplitude envelope structure, prosodic sensitivity, and phonological awareness in a sample of 56 typically-developing children and children with developmental dyslexia. We examine whether rise time sensitivity is linked to prosodic sensitivity, and whether prosodic sensitivity is linked to phonological awareness. Prosodic sensitivity was measured by two reiterant speech tasks modelled on Kitzen (2001). The children with developmental dyslexia were significantly impaired in the reiterant speech tasks and in the phonological awareness tasks (onset and rime awareness). There were significant predictive relations between basic auditory processing of amplitude envelope structure (in particular, rise time), prosodic sensitivity, phonological awareness, reading, and spelling. The auditory processing difficulties that characterise children with developmental dyslexia appear to impair their sensitivity to phrase-level prosodic cues such as metrical structure as well as to phonology, but in this study phonological and prosodic sensitivity made largely independent contributions to reading.     

Dyslexia and the double deficit hypothesis

The double deficit hypothesis (Bowers and Wolf 1993) maintains that children with both phonological and naming-speed deficits will be poorer readers than children with just one or neither of these deficits. In the present study, we drew on this hypothesis to help understand why some children have a serious reading impairment. In addition, by adding an orthographic factor, we extended it to a triple deficit hypothesis. Participants were 90 children aged 6 to 10 years. Dyslexic children, whose reading was low for age and for expected level, garden-variety poor readers, reading-level matched younger children, and low verbal IQ good readers, were compared. The dyslexic group was significantly lower then the garden-variety poor readers and the low verbal IQ good readers on most measures, and lower than the younger group on phonological measures. Findings support the double deficit hypothesis of Bowers and Wolf, and also the triple deficit hypothesis. Most of the poorest readers, nearly all of whom qualified as dyslexic, had a double or triple deficit in phonological, naming-speed, and orthographic skills. Conclusions were that dyslexia results from an overload of deficits in skills related to reading, for which the child cannot easily compensate.     

Verbal memory and phonological processing in dyslexia

This study examines whether two frequently reported causes of dyslexia, phonological processing problems and verbal memory impairments, represent a double‐deficit or whether they are two expressions of the same deficit. Two‐hundred‐and‐sixty‐seven Dutch children aged 10–14 with dyslexia completed a list‐learning task and several phonological tasks, together with a number of reading and spelling tests. The results indicate that phonological deficits and verbal memory impairments in dyslexia stem from the same root, which seemingly reflects an inaccurate encoding of the phonological characteristics of verbal information. This phonological encoding deficit is a negative predictor for both the reading and spelling skills of dyslexic children.     

The role of speed of processing, rapid naming, and phonological awareness in reading achievement

This study investigated the role of speed of processing, rapid naming, and phonological awareness in reading achievement. Measures of response time in motor, visual, lexical, grammatical, and phonological tasks were administered to 279 children in third grade. Measures of rapid object naming, phonological awareness, and reading achievement were given in second and fourth grades. Reading group comparisons indicated that poor readers were proportionally slower than good readers across response time measures and on the rapid object naming task. These results suggest that some poor readers have a general deficit in speed of processing and that their problems in rapid object naming are in part a reflection of this deficit. Hierarchical regression analyses further showed that when considered along with IQ and phonological awareness, speed of processing explained unique variance in reading achievement. This finding suggests that a speed of processing deficit may be an "extraphonological" factor in some reading disabilities.     

Auditory Sensory Processing and Phonological Development in High IQ and Exceptional Readers,Typically Developing Readers,and Children With Dyslexia: A Longitudinal Study

Phonological difficulties characterize children with developmental dyslexia across languages, but whether impaired auditory processing underlies these phonological difficulties is debated. Here the causal question is addressed by exploring whether individual differences in sensory processing predict the development of phonological awareness in 86 English-speaking lower- and middle-class children aged 8 years in 2005 who had dyslexia, or were age-matched typically developing children, some with exceptional reading/high IQ. The predictive relations between auditory processing and phonological development are robust for this sample even when phonological awareness at Time 1 (the autoregressor) is controlled. High reading/IQ does not much impact these relations. The data suggest that basic sensory abilities are significant longitudinal predictors of growth in phonological awareness in children.     

Working memory deficits in children with specific learning disorders

This article examines working memory functioning in children with specific developmental disorders of scholastic skills as defined by ICD-10. Ninety-seven second to fourth graders with a minimum IQ of 80 are compared using a 2 x 2 factorial (dyscalculia vs. no dyscalculia; dyslexia vs. no dyslexia) design. An extensive test battery assesses the three subcomponents of working memory described by Baddeley (1986): phonological loop, visual-spatial sketchpad, and central executive. Children with dyscalculia show deficits in visual-spatial memory; children with dyslexia show deficits in phonological and central executive functioning. When controlling for the influence of the phonological loop on the performance of the central executive, however, the effect is no longer significant. Although children with both reading and arithmetic disorders are consistently outperformed by all other groups, there is no significant interaction between the factors dyscalculia and dyslexia.     

Implicit sublexical phonological processing in an acquired dyslexic patient

We report a case study of an acquired dyslexic subject, who on tasks standardly used to assess acquired dyslexia showed no evidence of having any access to sublexical phonological information. However, on a lexical decision task, he showed normal effects of spelling regularity for low-frequency words. Since this effect is typically attributed to the use of sublexical phonological information in word recognition, it appears that sublexical phonological processing is occurring for this subject. The spelling regularity effect is discussed with respect to models of written word recognition and to acquired dyslexia. It is suggested that the reason for the discrepancy in test results may be that the types of explicit tasks previously used in the neuropsychological literature on dyslexia, which require conscious awareness of phonological representations, are not sensitive to implicit processing.     

Growth in Precursor and Reading‐Related Skills: Do Low‐Achieving and IQ‐Discrepant Readers Develop Differently?

Poor readers who met low achievement and IQ‐discrepancy definitions of reading disability were compared with nonimpaired readers on their development of eight precursor and reading‐related skills to evaluate developmental differences prior to students’ identification as reading disabled. Results indicated no evidence for differences between the two groups of poor readers in the development of the eight skills, with three exceptions. Students in the IQ‐discrepant group demonstrated greater growth in letter sound knowledge, greater mean performance in visual‐motor integration at the beginning of first grade, and greater deceleration in rapid naming of letters. When compared to the nonimpaired group, low‐achieving readers demonstrated poorer performance and development in all skills, while the IQ‐discrepant readers demonstrated poorer performance and development in phonemic awareness, rapid naming of letters and objects, spelling, and word reading. The largely null results for comparisons between the two groups of poor readers challenges the validity of the two‐group classification of reading disabilities based on IQ‐discrepancy.