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.     

Developmental dyslexia: exploring how much phonological and visual attention span disorders are linked to simultaneous auditory processing deficits

The simultaneous auditory processing skills of 17 dyslexic children and 17 skilled readers were measured using a dichotic listening task. Results showed that the dyslexic children exhibited difficulties reporting syllabic material when presented simultaneously. As a measure of simultaneous visual processing, visual attention span skills were assessed in the dyslexic children. We presented the dyslexic children with a phonological short-term memory task and a phonemic awareness task to quantify their phonological skills. Visual attention spans correlated positively with individual scores obtained on the dichotic listening task while phonological skills did not correlate with either dichotic scores or visual attention span measures. Moreover, all the dyslexic children with a dichotic listening deficit showed a simultaneous visual processing deficit, and a substantial number of dyslexic children exhibited phonological processing deficits whether or not they exhibited low dichotic listening scores. These findings suggest that processing simultaneous auditory stimuli may be impaired in dyslexic children regardless of phonological processing difficulties and be linked to similar problems in the visual modality.     

Integration of the visual and auditory networks in dyslexia: a theoretical perspective

In addition to an intrinsic difficulty in reading and spelling, one of the defining characteristics of dyslexia is an enduring and pervasive difficulty in phonological coding, such that dyslexic readers find it particularly challenging to process and manipulate the constituent sounds of a language. Coexistent with this finding is the evidence that some dyslexic readers also demonstrate subtle sensory coding problems in the visual and auditory domains. Few theories have been proposed to unite these different findings within a coherent model of reading. Here the evidence for visual, auditory and phonological coding problems in dyslexia is briefly reviewed, and a hypothesis is proposed for how adequate early sensory coding may be intrinsic to phonological awareness and subsequent reading ability. In this hypothesis, a cortical network is assumed that incorporates the visual, auditory and phonological skills of reading. The visual sub‐component of the network is mediated by the dorsal visual pathway, which is responsible for the accurate spatial encoding of letters, words and text. The auditory component of the network in pre‐readers is intrinsic to the development of phonological sensitivity, and then grapheme‐phoneme assimilation as reading skills develop. In this hypothesis, some of the symptoms of dyslexia may result from subtle problems in the encoding of both visual and auditory information and their role in maintaining the synchronicity of the reading network.     

Do dyslexic and other poor readers differ in reading-related cognitive skills?

The rationale for the study was that if dyslexic and garden-variety poor readers differ in reading-related cognitive skills, there is justification for believing dyslexia to be a distinct entity. Subjects were 110 children aged 6 to 10 years, divided into groups of dyslexic poor readers varying in verbal IQ, garden-variety poor readers, and good readers. Findings suggest that there are valid grounds for believing that dyslexia is a separate entity from garden-variety poor reading, and that it is found among children at all verbal IQ levels. Poor phonological awareness and nonword reading, in relation to normal readers, were shared by dyslexic and garden-variety poor readers. Deficits unique to dyslexic poor readers were problems in both automatic visual recognition and phonological recoding of graphic stimuli. The study supports the phonological-core variable-difference model of Stanovich (1988) in that both dyslexic and garden-variety poor readers showed phonological processing deficits, but they were more extensive in dyslexics.     

Auditory and motor rhythm awareness in adults with dyslexia

Children with developmental dyslexia appear to be insensitive to basic auditory cues to speech rhythm and stress. For example, they experience difficulties in processing duration and amplitude envelope onset cues. Here we explored the sensitivity of adults with developmental dyslexia to the same cues. In addition, relations with expressive and receptive rhythm tasks, such as tempi recognition and manual tapping to a metronome, were explored. Our goal was to investigate whether the auditory deficits seen in dyslexia are specific to cues to speech rhythm and stress, or are part of a wider rhythmic awareness problem. A group of 19 undergraduate students with dyslexia were compared with 20 age‐ and ability‐matched controls. The findings confirmed a relationship between auditory rhythm sensitivity and literacy in adults, as well as showing an association with metronome inter‐tap‐interval variability.     

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.     

Phonological processing skills and deficits in adult dyslexics

This article presents 4 experiments aimed at defining the primary underlying phonological processing deficit(s) in adult dyslexia. 5 phonological processes, all involving spoken language, were studied: phoneme perception, phoneme awareness, lexical retrieval of phonology, articulatory speed, and phonetic coding in verbal short-term memory. 2 differently ascertained adult dyslexic groups, familial dyslexics (n = 15) and clinic dyslexics (n = 15), were the subjects in each experiment. These dyslexic groups were chosen because deficits that persist until adulthood and that are found in differently ascertained dyslexic groups are more likely to be primary. Each dyslexic group was compared to 2 control groups, chronological age (CA) controls who were similar in age and sex, and younger reading age (RA) controls who were similar in reading age and sex. The main finding was a clear deficit in phoneme awareness in both dyslexic groups, with each dyslexic group performing significantly worse than both CA and RA controls. Moreover, performance on the 2 phoneme awareness tasks together uniquely accounted for substantial variance in nonword reading. The clinic but not the familial dyslexics appeared to have an additional deficit in verbal short-term memory. No clear deficits were found in either dyslexic group in phoneme perception, lexical retrieval, or articulatory speed.     

Cognitive processing skills and developmental dyslexia in Chinese

The purpose of the present study was twofold: (a) to examine the extent to which Chinese dyslexic children experience deficits in phonological and orthographic processing skills and (b) to examine if Chinese dyslexia is associated with deficits in Planning, Attention, Simultaneous, and Successive (PASS) processing. A total of 27 Grade 4 children with dyslexia (DYS), 27 Grade 4 chronological age (CA) controls, and 27 Grade 2 reading age (RA) controls were tested on measures of phonological awareness, rapid naming, phonological memory, PASS, reading accuracy, and reading fluency. The results indicated that the DYS group performed significantly poorer than the CA and RA groups on both measures of phonological awareness and on a measure of orthographic processing but comparably to the RA group on a measure of rapid naming and both measures of phonological memory. In regard to the PASS processing skills, the DYS group performed worse than the CA controls on Successive and Simultaneous processing but comparably to the RA group on all PASS processing skills. Implications of these findings for early identification and intervention of reading difficulties are discussed.     

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.     

Phonemic—Morphemic dissociation in university students with dyslexia: an index of reading compensation?

A phonological deficit constitutes a primary cause of developmental dyslexia, which persists into adulthood and can explain some aspects of their reading impairment. Nevertheless, some dyslexic adults successfully manage to study at university level, although very little is currently known about how they achieve this. The present study investigated at both the individual and group levels, whether the development of another oral language skill, namely, morphological knowledge, can be preserved and dissociated from the development of phonological knowledge. Reading, phonological, and morphological abilities were measured in 20 dyslexic and 20 non-dyslexic university students. The results confirmed the persistence of deficits in phonological but not morphological abilities, thereby revealing a dissociation in the development of these two skills. Moreover, the magnitude of the dissociation correlated with reading level. The outcome supports the claim that university students with dyslexia may compensate for phonological weaknesses by drawing on morphological knowledge in reading.     

Adult developmental dyslexia in a shallow orthography: Are there subgroups?

The existence and stability of subgroups among adult dyslexic readers of a shallow orthography was explored by comparing three different cluster analyses based on previously suggested combinations of two variables. These were oral reading speed versus accuracy, word versus pseudoword reading speed, and phonological awareness versus rapid naming. The three analyses were conducted with the same group of dyslexic adults. Each analysis produced three subgroups, corresponding to ones previously suggested in the literature. However, the subgroups had only little overlap from one analysis to another. Each clustering produced somewhat different subgroup profiles in phonological processing, reading, intelligence, temporal acuity, and sensory short-term memory. However, the shared difficulties of the solutions in several language-related and sensory tasks suggest the conclusion that developmental dyslexia does not causally consist of subgroups, at least in shallow orthographies. Further, the shared sensory difficulties suggest that impaired temporal acuity and sensory short-term memory may reflect the severity of a primary disorder that dyslexic readers cannot compensate by strategies.     

Computerised screening for dyslexia in adults

Identifying dyslexia in adulthood presents particular challenges because of complicating factors such as acquisition of compensatory strategies, differing degrees of intervention and the problem of distinguishing dyslexic adults from those whose literacy difficulties have non‐cognitive causes. One of the implications is that conventional literacy measures, per se, do not provide a satisfactory basis for screening for dyslexia in adulthood as some dyslexic adults have above‐average literacy skills and some non‐dyslexic adults have very poor literacy skills. This study examined an alternative approach to dyslexia screening, using three tests that depend heavily on phonological processing, lexical access and working memory, but which are not conventional measures of literacy. Using these tests, which are computer delivered, 70 dyslexic adults from three different types of educational institution were compared with 69 non‐dyslexic adults from the same institutions. The results showed that the dyslexic and non‐dyslexic groups were significantly different on all three computer‐based tests, with an average effect size of 1.55. Adaptive versions of these tests were then created to reduce overall administration time for the suite to about 15 minutes. Analysis showed that the combined scaled scores from the adaptive versions of the three tests significantly discriminated the dyslexic from the non‐dyslexic group with an increased effect size of 2.07 and with a sensitivity rate of 90.6% and a specificity rate of 90.0%. It was concluded that this approach is a valid and useful method of identifying dyslexia in adulthood, which, given the ease of administration to large numbers of adults, has noted advantages for education and employment.     

Is dyslexia a form of specific language impairment? a comparison of dyslexic and language impaired children as adolescents

Two groups of adolescents with a childhood history of language impairment were compared with a group of developmentally dyslexic young people of the same age and nonverbal ability. The study also included two comparison groups of typically developing children, one of the same age as those in the clinical groups, and a younger comparison group of similar reading level to the dyslexic students. Tests of spoken and written language skills revealed that the adolescents with dyslexia were indistinguishable from those with resolved language impairments on spoken language tasks, and both groups performed at age-expected levels. However, both dyslexic readers and those with resolved specific language impairments showed deficits in phonological awareness. On written language tasks, a different pattern of performance was apparent. In reading and spelling, adolescents with dyslexia performed only as well as those with persistent oral language impairments and younger controls. However, their reading comprehension was better. The theoretical and educational implications of these findings are discussed.     

Phonological recoding deficit in working memory of dyslexic teenagers

The picture span performance of developmental dyslexic teenagers (mean age 14 years 1 month) was compared to the picture span performance of both RA (mean age 9 years 0 month) and chronological age match controls (mean age 14 years 1 month). Three stimulus lists were manipulated for visual and phonological similarity. Findings indicated that all three groups showed a significant phonological similarity effect but only the dyslexic group showed a significant visual similarity effect. The presence of dual visual‐verbal coding is postulated to be responsible for the ‘noisy’ encoding which others (e.g. Johnston and Anderson, 1998; Swan and Goswami, 1997) have suggested is a root cause of dyslexia. The results are discussed in terms of developmental deficits in the central executive of the working memory system.     

Persistence of phonological processing deficits in college students with dyslexia who have age-appropriate reading skills

This study investigated the phonological processing skills of university students with dyslexia. Fifty-nine students participated in this study: 28 with reading disabilities based on recent psychological assessments and a history of early and persistent reading problems; and 31 controls. The two groups did not differ on estimates of verbal and nonverbal abilities. The dyslexia group performed significantly less well on standardized measures of reading and spelling. However, the dyslexia group scores on these measures fell within the average range. The main dependent variables were subsumed under three areas of phonological processing: phonological awareness, phonological recoding in lexical access, and phonological recoding in working memory. The control group performed significantly better on all phonological processing measures, particularly those measures involving accuracy and response times. Despite age-appropriate performances on standardized reading and spelling measures, phonological processing deficits persisted in the dyslexia group. These findings support the causal role of phonological awareness in the acquisition of reading skills and indicate that differences in phonological processing skills are still evident in a sample of university students with dyslexia compared a group matched on age and education.     

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.     

What can spelling errors tell us about the causes and treatment of dyslexia?

Until recently the majority of research undertaken into dyslexia focused on English‐speaking dyslexics, who tend to make significantly more phonological than visual errors. This led to a major assumption about the possible cause of dyslexia being a lack of phonological awareness. According to the phonological deficit theory, the level of phonological consistency of a language determines not only the reading speed but also the amount and types of reading and spelling errors made by dyslexic people. This theory has been seriously challenged by the results of a number of studies in more phonologically consistent languages, such as Greek, Italian and Japanese, where morphology seemed to play a more crucial role than the phonological structure of a language per se. The 116 dyslexic people who took part in this experiment were matched on age, sex, IQ and psycho‐educational performance. A total of 58 US English‐speaking dyslexic people were compared to 58 Greek dyslexic people. Both groups met the diagnostic criteria. Results demonstrated that Greek dyslexics were found to make significantly fewer phonological errors (11.0%) than the US dyslexics (85.5%, p < .000), but comparatively more visual (66.8% to US 14.0%, P < .000) and grammatical errors (22.2% to US 0.1%, p < .000) than their English‐speaking counterparts. These data showed highly significant quantitative and qualitative spelling differences. Greek dyslexics could be accurately differentiated from the US English dyslexics based on the three types of spelling errors.     

Effects of reading and writing on cerebral laterality in good readers and children with dyslexia.

The present study evaluated the idea that the hemisphere-specific cognitive demands of reading and writing may induce task-specific maladaptive patterns of language lateralization in children with dyslexia. Situation-specific lateralization was examined in a repeated measures design under three dichotic listening conditions: baseline, concurrent reading, and concurrent writing. Twelve males with phonological dyslexia, 8 to 12 years old, were compared to 12 age-matched and 12 younger reading-matched good readers. Lateralization patterns were examined for condition-specific relationships to pseudoword decoding, word recognition, reading comprehension, spelling, and arithmetic. The results show that dyslexia is not related to incomplete lateralization or to a failure to inhibit verbal processing in the right hemisphere during reading and writing. Reading increased the lateralization of the children with dyslexia, which had a negative relation to arithmetic; writing caused a decrease in lateralization, which was linked specifically to deficits in phonological decoding and visual word recognition. The results suggest that children with dyslexia suffer from a selective linguistic vulnerability to left-hemisphere interference from the idiosyncratic attentional and processing demands of particular school tasks. Dyslexia is a much more dynamic and environmentally sensitive disorder than previously thought.     

Effectiveness of computerised spelling training in children with language impairments: a comparison of modified and unmodified speech input

This study evaluated a computerised program for training spelling in 8‐ to 13‐year‐olds with receptive language impairments. The training program involved children typing words corresponding to pictured items whose names were spoken. If the child made an error or requested help, the program gave phonological and orthographic cues to build up the word's spelling. Eleven children received this training with ordinary speech, and eleven had the same program but with speech modified to lengthen and amplify dynamic portions of the signal. Nine children were in an untrained control group. Trained children completed between 6 and 29 training sessions each of 15 minutes, at a rate of 3 to 5 sessions per week, with an average of over 1000 trials. Children were assessed before and after training. Trained children learned an average of 1.4 novel spellings per session. The trend was for children presented with modified speech to do less well than those trained with ordinary speech, regardless of whether they had auditory temporal processing impairments. Trained groups did not differ from the untrained control group in terms of gains made on standardised tests of spelling or word and nonword reading. This study confirms the difficulty of training literacy skills in children with severe language impairments. Individual words may be learned, but more general knowledge of rule‐based phonological skills is harder to acquire.