Auditory sensory deficits in developmental dyslexia: A longitudinal ERP study

Aim: Developmental dyslexia is basically defined as a learning disorder characterized by reading, writing, spelling, and word comprehension difficulties. Phonological deficits in dyslexia are well established in literature, yet, research also indicates some visuospatial difficulties. The aim of this study was to examine the visuospatial functions in Turkish children with dyslexia and to show the interrelationship of visuospatial perception, visual memory, and executive functions. Methods: The sample of this study was composed of 20 children (9 female and 11 male) with developmental dyslexia and 20 age-matched controls (11 female and 9 male). The children in dyslexia group were previously diagnosed as dyslexic according to Diagnostic and Statistical Manual of Mental Disorder-IV criteria in a private rehabilitation center. Rey-Osterreich complex figure test (ROCF), Clock Drawing Test (CDT), and Judgment of Line Orientation test (JLOT) were used to evaluate visuospatial functions of the children. Results: Comparison analyses showed that dyslexia group significantly differed from the control group in all visuospatial test scores (P < 0.05 for all). In addition, a positive correlation was present between JLOT score and ROCF direct copying score, ROCF immediate memory score, ROCF delayed memory score, and CDT score for the dyslexic group (P < 0.05 for all). Conclusion: Our findings confirm the presence of visuospatial problems in dyslexia and highlight the importance of interaction between perceptual and executive processes indicating a more fundamental cognitive deficit.

Although dyslexia can be individuated in many different ways, it has only three discernable sources: a visual deficit that affects the perception of letters, a phonological deficit that affects the perception of speech sounds, and an audio-visual deficit that disturbs the association of letters with speech sounds. However, the very nature of each of these core deficits remains debatable. The phonological deficit in dyslexia, which is generally attributed to a deficit of phonological awareness, might result from a specific mode of speech perception characterized by the use of allophonic (i.e., subphonemic) units. Here we will summarize the available evidence and present new data in support of the “allophonic theory” of dyslexia. Previous studies have shown that the dyslexia deficit in the categorical perception of phonemic features (e.g., the voicing contrast between /t/ and /d/) is due to the enhanced sensitivity to allophonic features (e.g., the difference between two variants of /d/). Another consequence of allophonic perception is that it should also give rise to an enhanced sensitivity to allophonic segments, such as those that take place within a consonant cluster. This latter prediction is validated by the data presented in this paper.

Auditory identification of frequency-modulated sweeps and reading difficulties in Chinese

ABSTRACTThis study investigates whether developmental dyslexia involves an impairment in implicit phonological representations, as distinct from orthographic representations and metaphonological skills. A group of adults with dyslexia was matched with a group with no history of speech/language/literacy impairment. Tasks varied in the demands made on (implicit) phonological representations versus metalinguistic analysis/manipulation, and controlled the contribution of phonological versus orthographic representations by including both a segmental and an equivalent suprasegmental (nonorthographic) version of each task. The findings show a dissociation between metaphonological skills and implicit phonological representations, with the dyslexic group impaired in metaphonological manipulation skills in both segmental and suprasegmental tasks, but not in implicit knowledge of phonological contrasts.

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.

Early neuroimaging studies exploring the neurobiological correlates of the phonological deficit in dyslexia were restricted to adult probands with dyslexia due to the exposure to radioactivity in the course of PET measurements. The differences in activation between normal adult readers and adults with dyslexia recorded in these studies left open the issue of whether or not these are indeed fundamental activation deficits or only a reflection of lifelong experience with poor reading and writing skills and thus should be interpreted as a sign of compensation. Development of fMRI in recent years has enabled the investigation of children with dyslexia in order to explore the neurobiological activation patterns that underlie dyslexia. On the whole, the imaging findings in children and adults with dyslexia indicate that the left-hemisphere inferior frontal differences in activation, as well as the dorsal and ventral temporal differences in activation observed in all age groups during the processing of phonological language tasks are to be regarded as a fundamental biological deficit in dyslexia. Right-hemisphere differences in activation, which in German-speaking areas are observable in adults but only rarely in children with dyslexia, might, on the other hand, be regarded as a sign of developmental compensation.

It has been suggested that auditory and visual sequential processing deficits contribute to phonological disorders in developmental dyslexia. As an alternative explanation to a phonological deficit as the proximal cause for reading disorders, the visual attention span hypothesis (VA Span) suggests that difficulties in processing visual elements simultaneously lead to dyslexia, regardless of the presence of a phonological disorder. In this study, we assessed whether deficits in processing simultaneously displayed visual or auditory elements is linked to dyslexia associated with a VA Span impairment. Sixteen children with developmental dyslexia and 16 age-matched skilled readers were assessed on visual and auditory search tasks. Participants were asked to detect a target presented simultaneously with 3, 9, or 15 distracters. In the visual modality, target detection was slower in the dyslexic children than in the control group on a “serial” search condition only: the intercepts (but not the slopes) of the search functions were higher in the dyslexic group than in the control group. In the auditory modality, although no group difference was observed, search performance was influenced by the number of distracters in the control group only. Within the dyslexic group, not only poor visual search (high reaction times and intercepts) but also low auditory search performance (d′) strongly correlated with poor irregular word reading accuracy. Moreover, both visual and auditory search performance was associated with the VA Span abilities of dyslexic participants but not with their phonological skills. The present data suggests that some visual mechanisms engaged in “serial” search contribute to reading and orthographic knowledge via VA Span skills regardless of phonological skills. The present results further open the question of the role of auditory simultaneous processing in reading as well as its link with VA Span skills.

Several studies have signaled grammatical difficulties in individuals with developmental dyslexia. These difficulties may stem from a phonological deficit, but may alternatively be explained through a domain-general deficit in statistical learning. This study investigates grammar in children with and without dyslexia, and whether phonological memory and/or statistical learning ability contribute to individual differences in grammatical performance. We administered the CELF “word structure” and “recalling sentences” subtests and measures of phonological memory (digit span, nonword repetition) and statistical learning (serial reaction time, nonadjacent dependency learning) among 8- to 11-year-old children with and without dyslexia (N= 50 per group). Consistent with previous findings, our results show subtle difficulties in grammar, as children with dyslexia achieved lower scores on the CELF (word structure:p= .0027, recalling sentences:p= .053). While the two phonological memory measures were found to contribute to individual differences in grammatical performance, no evidence for a relationship with statistical learning was found. An error analysis revealed errors in irregular morphology (e.g., plural and past tense), suggesting problems with lexical retrieval. These findings are discussed in light of theoretical accounts of the underlying deficit in dyslexia.

The very common association between developmental dyslexia and phonological deficits had led to the widespread suggestion that the core deficit in dyslexia is in phonological processing. However, causality has never been clearly established; indeed there are compelling reasons to believe that the aetiology may be primarily within the visual system. This stems from recent attempts to explain the various stages involved in decoding the letter stream in neuronal terms and anchoring the reading stages firmly in the known neuroanatomical and neurophysiological basis of the processing of visual stimuli. A central component of this framework is the role played by visuo-spatial attention in parsing the stream of letters at different spatial and temporal scales. It is proposed that a deficit in this process either from a lesion in the dorsal visual stream or in the inputs it receives from the magnocellular pathway can lead to poor reading abilities. Such impaired orthographic processing may even lead to some of the phonological impairments seen in dyslexics.

Recent research with English developmental dyslexics comparing the picture naming performance of these children to the picture naming performance of non-dyslexic (‘garden variety’) poor readers, reading age matched controls and chronological age matched controls has suggested that a selective difficulty in retrieving the phonological codes of known names on demand underlies the picture naming deficit found in developmental dyslexia (Swan & Goswami, Picture naming deficits in developmental dyslexia: the phonological representations hypothesis, Brain and Language, 56 (1997), 334–353). If the underlying causal factors in dyslexia are independent of the orthography that the child is learning to read, then a difficulty in retrieving the phonological codes of known names on demand should also be found in developmental dyslexics who are learning to read other languages. We therefore set out to replicate Swan and Goswami’s study with a group of German developmental dyslexics. We were interested to see whether a phonological deficit is characteristic of dyslexia in all orthographies, even those, such as German, in which high orthographic transparency means that dyslexic children read with considerable accuracy.

Two studies were conducted to investigate visual attention deficits in dyslexia. In Experiment 1, adults with dyslexia and age- and IQ-matched controls completed a simple cueing task; participants responded to briefly presented (20 ms) eccentric targets (3°, 6°, or 9°) with a key press. In Experiment 2, the same participants completed a saccade version of the task, and saccade amplitude, accuracy, and latency were measured. The results revealed comparable performance between the groups on the manual reaction time task. The groups also performed similarly in saccade accuracy and latency. Moreover, neither group showed a visual field asymmetry in their performance, with the exception that adults with dyslexia showed longer saccade latency for 9° targets presented to their left visual field than did controls. However, on the latter measure, the majority (78%) of those with dyslexia performed within the range of the control group. Correlational analyses revealed associations between reading and phoneme awareness in both groups, but phoneme awareness was not associated with visual attention in adult dyslexics. Together, the results are not compatible with a visual attention deficit in adult dyslexia, while they provide support for the phonological deficit hypothesis.

Phonological dyslexics (Ph-DYS) are characterized by a phonological deficit, while surface dyslexics (S-DYS) are characterized by an orthographic deficit. Four issues were addressed in this study. First, we determined the proportion of Ph-DYS and S-DYS in a population of French dyslexics by applying Castles and Coltheart's (1993) regression method to two previously unused diagnostic measures: pseudo-word and irregular-word processing time. Thirty-one dyslexics were matched to 19 average readers of the same age (10 years, CA controls) and to 19 younger children of the same reading level (8 years, RL controls). Compared to CA controls, there were more Ph-DYS than S-DYS. Compared to RL controls, there were still a high number of Ph-DYS; however, the S-DYS profile almost disappeared. Next, we examined the reliability of these subtypes across different measures of phonological and orthographic skills. Compared to RL controls, both groups of dyslexics were found to be impaired only in phonological skills, either in processing time (Ph-DYS) or in accuracy (S-DYS). Then we assessed the moment at which the two dissociated profiles emerged in the course of cognitive development. In order to do so, we examined earlier longitudinal data, collected when the children were 7 and 8 years old, and found that only the S-DYS's orthographic deficit increased with development. Last, we looked at whether the Ph-DYS and S-DYS profiles were associated with other specific cognitive deficits. Specific deficits in phonemic awareness and in phonological short-term memory were found for both Ph-DYS and S-DYS. These data suggest that developmental dyslexia could be largely accounted for by an underlying phonological impairment.

Learning to read involves cross-modal binding processes, that is, the association between visual and phonological information in the mapping of written forms (graphemes) to phonological codes. The present study examined visual-phonological binding in a memory binding task, comparing a group of children with dyslexia with a control group of typical readers, matched for age, grade, and sex. Children were required to memorize the association between 8 shapes and nonwords presented in association for 4 times, placed either in fixed or variable spatial locations across trials. The results showed that children with dyslexia have deficits in cross-modal memory binding and are not able to use spatial location as an effective cue to bind information, as it was observed for control children. In addition, children with dyslexia made more phonological errors and binding errors than the control group. A purely phonological deficit in dyslexia does not explain the overall pattern of results, and dyslexia may involve deficits in 1 or more types of processes, including the capacity to bind visual to phonological information. Thus, assessment of binding processes may have implications both for diagnosis and treatment.

Due to the fact that it is frequently difficult to identify their etiological origins, reading and writing difficulties have inconsistent terminology in the literature. This article is a review and attempts to initiate a discussion about visual dyslexia. The authors pose the question whether - in the context of new neuroimaging methods and the neurosciences broadly defined - there exist reading and writing difficulties that stem from impaired functioning of the visual system and whether they can be assigned to developmental dyslexia. If it is assumed that developmental dyslexia is linguistic in nature, these are phonological deficits that come to the fore in children entering the world of reading. These phonological processing deficits impair word decoding (word identification), making word recognition impossible, thus preventing access to higher-order linguistic processes, that is comprehending meaning from texts or building one’s own narratives.

Developmental dyslexia is a cognitive disorder characterized by difficulties in linguistic processing. Our purpose is to distinguish subtypes of developmental dyslexia by the level of speech–EEG frequency entrainment (δ: 1–4; β: 12.5–22.5; γ1: 25–35; and γ2: 35–80 Hz) in word/pseudoword auditory discrimination. Depending on the type of disabilities, dyslexics can divide into two subtypes—with less pronounced phonological deficits (NoPhoDys—visual dyslexia) and with more pronounced ones (PhoDys—phonological dyslexia). For correctly recognized stimuli, the δ-entrainment is significantly worse in dyslexic children compared to controls at a level of speech prosody and syllabic analysis. Controls and NoPhoDys show a stronger δ-entrainment in the left-hemispheric auditory cortex (AC), anterior temporal lobe (ATL), frontal, and motor cortices than PhoDys. Dyslexic subgroups concerning normolexics have a deficit of δ-entrainment in the left ATL, inferior frontal gyrus (IFG), and the right AC. PhoDys has higher δ-entrainment in the posterior part of adjacent STS regions than NoPhoDys. Insufficient low-frequency β changes over the IFG, the inferior parietal lobe of PhoDys compared to NoPhoDys correspond to their worse phonological short-term memory. Left-dominant 30 Hz-entrainment for normolexics to phonemic frequencies characterizes the right AC, adjacent regions to superior temporal sulcus of dyslexics. The pronounced 40 Hz-entrainment in PhoDys than the other groups suggest a hearing “reassembly” and a poor phonological working memory. Shifting up to higher-frequency γ-entrainment in the AC of NoPhoDys can lead to verbal memory deficits. Different patterns of cortical reorganization based on the left or right hemisphere lead to differential dyslexic profiles.