Developmental dyslexia: specific phonological deficit or general sensorimotor dysfunction?

Pediatric neuro-ophthalmology

PURPOSE OF REVIEW

This review will update the ophthalmologist on recent developments in pediatric neuro-ophthalmology.

RECENT FINDINGS

Research into the genetics of congenital strabismus syndromes has brought new insights into the development of the ocular motor system. There is also new literature on childhood ocular myasthenia gravis and childhood neurosarcoidosis. The results of three different surgical treatments for congenital nystagmus are described. Reviews on cortical visual impairment, dyslexia, Aicardi syndrome, and neuronal ceroid lipofuscinosis are presented.

SUMMARY

Pediatric neuro-ophthalmology is a diverse and challenging field. As we strive to provide excellent care to these patients, we will use the results of basic science, genetic, and neurobiological research.

Evaluation of Selected Auditory Tests in School-Age Children Suspected of Auditory Processing Disorders

OBJECTIVE

To compare the auditory function of normal-hearing children attending mainstream schools who were referred for an auditory evaluation because of listening/hearing problems (suspected auditory processing disorders [susAPD]) with that of normal-hearing control children.

DESIGN

Sixty-five children with a normal standard audiometric evaluation, ages 6-14 yr (32 of whom were referred for susAPD, with the rest age-matched control children), completed a battery of four auditory tests: a dichotic test of competing sentences; a simple discrimination of short tone pairs differing in fundamental frequency at varying interstimulus intervals (TDT); a discrimination task using consonant cluster minimal pairs of real words (CCMP), and an adaptive threshold task for detecting a brief tone presented either simultaneously with a masker (simultaneous masking) or immediately preceding it (backward masking). Regression analyses, including age as a covariate, were performed to determine the extent to which the performance of the two groups differed on each task. Age-corrected z-scores were calculated to evaluate the effectiveness of the complete battery in discriminating the groups.

RESULTS

The performance of the susAPD group was significantly poorer than the control group on all but the masking tasks, which failed to differentiate the two groups. The CCMP discriminated the groups most effectively, as it yielded the lowest number of control children with abnormal scores, and performance in both groups was independent of age. By contrast, the proportion of control children who performed poorly on the competing sentences test was unacceptably high. Together, the CCMP (verbal) and TDT (nonverbal) tasks detected impaired listening skills in 56% of the children who were referred to the clinic, compared with 6% of the control children. Performance on the two tasks was not correlated.

CONCLUSIONS

Two of the four tests evaluated, the CCMP and TDT, proved effective in differentiating the two groups of children of this study. The application of both tests increased the proportion of susAPD children who performed poorly compared with the application of each test alone, while reducing the proportion of control subjects who performed poorly. The findings highlight the importance of carrying out a complete auditory evaluation in children referred for medical attention, even if their standard audiometric evaluation is unremarkable.

The development of children at familial risk for dyslexia: birth to early school age

Children at risk for familial dyslexia (n = 107) and their controls (n = 93) have been followed from birth to school entry in the Jyvaskyla Longitudinal study of Dyslexia (JLD) on developmental factors linked to reading and dyslexia. At the point of school entry, the majority of the at-risk children displayed decoding ability that fell at least 1 SD below the mean of the control group. Measures of speech processing were the earliest indices to show both group differences in infancy and also significant predictive associations with reading acquisition. A number of measures of language, including phonological and morphological skill collected repeatedly from age three, revealed group differences and predictive correlations. Both the group differences and the predictive associations to later language and reading ability strengthened as a function of increasing age. The predictions, however, tend to be stronger and the spectrum of significant correlations wider in the at-risk group. These results are crucial to early identification and intervention of dyslexia in at-risk children.

Developmental dyslexia: ERP correlates of anomalous phonological processing during spoken word recognition

Ample evidence suggests that developmental dyslexia results from a phonological deficit that may not be reducible to a low-level auditory deficit. Yet, on-line phonological processing (in)capacities in dyslexics remain virtually unexplored, as studies have typically focused on either meta-phonological awareness tasks or, at the other extreme, basic perceptual tasks. The present study investigates event-related potential (ERP) correlates of implicit phonological processing during the recognition of spoken words in dyslexic and normally reading children (7-10 years). We examined general ERP morphology and alliteration priming effects on ERP measures in an auditory lexical decision task. Primes were words (Experiment 1) and non-words (Experiment 2). Alliteration priming effects suggested a distinct pattern of normal versus anomalous aspects of spoken word processing in dyslexic children. Whereas dyslexics showed deviant priming effects in earlier time windows encompassing the N1 and N2, later N400 priming effects were comparable to those of normal readers. The same pattern of results was also present in group comparisons of general ERP morphology. These findings suggest that dyslexics have selective processing anomalies at an earlier phonetic/phonological level, while processing at a later phonological/lexical level proceeds normally. In particular, our results indicate an anomalous contribution of phonological (word onset) information to the processing of spoken words, which may be related to time-course aspects of phonetic/phonological processing.

Current status of treatments for dyslexia: critical review

The acquisition of reading is a complex neurobiologic process. Identifying the most effective instruction and remedial intervention methods for children at risk of developing reading problems and for those who are already struggling is equally complex. This article aims to provide the clinician with a review of more current findings on the prevention and remediation of reading problems in children, along with an approach to considering the diagnosis and treatment of a child with dyslexia. The first part of the review describes interventions targeted at preventing reading difficulties in the at-risk younger child. The second part of the review discusses the efficacy of approaches to treat the older, reading-disabled child ("intervention studies"). Factors that impact the response to treatment are also discussed, as are neuroimaging studies that offer insight into how the brain responds to treatment interventions. With appropriate instruction, at-risk readers can become both accurate and fluent readers. In contrast, although intensive, evidence-based remedial interventions can markedly improve reading accuracy in older, reading-disabled children, they have been significantly less effective in closing the fluency gap. Owing to the dynamic course of language development and the changes in language demands over time, even after a child has demonstrated a substantial response to treatment interventions, his or her subsequent progress should be carefully tracked to ensure optimal progress toward the development of functional reading and written language skills.

The reliability and validity of tasks measuring perception of rapid sequences in children with dyslexia

BACKGROUND

Claims that children with reading and oral language deficits have impaired perception of sequential sounds are usually based on psychophysical measures of auditory temporal processing (ATP) designed to characterise group performance. If we are to use these measures (e.g., the Tallal, 1980, Repetition Test) as the basis for intervention in language and literacy deficits, we need to demonstrate that they can effectively quantify individual differences. Therefore, questions of standardisation, reliability and construct validity can no longer be ignored.

METHOD

We explored these issues in three studies: (i) 52 Dyslexics and Good Readers aged 8 to 11 years performed a task requiring perception of rapid sequences (PRS) based on the Tallal Repetition Test; (ii) a subgroup of the initial sample was retested on the task three to four months later, and after extended practice; (iii) a further subgroup then completed a rate of auditory processing task using a backward recognition masking paradigm.

RESULTS

With a standardised methodology, we were able to replicate previous results with the PRS task, and demonstrate moderate reliability of measurement across time and practice. However, there were large effects of exposure and practice, and the task did not seem useful for identifying absolute and continuing deficits in given individuals.

CONCLUSIONS

Our results call into question the use of this type of task as an individual measure of ATP. Neither is it certain that it is capturing what is currently understood as ATP.

In search of the auditory, phonetic, and/or phonological problems in dyslexia: context effects in speech perception

There is a growing consensus that developmental dyslexia is associated with a phonological-core deficit. One symptom of this phonological deficit is a subtle speech-perception deficit. The auditory basis of this deficit is still hotly debated. If people with dyslexia, however, do not have an auditory deficit and perceive the underlying acoustic dimensions of speech as well as people who read normally, then why do they exhibit a categorical-perception deficit? A potential answer to this conundrum lies in the possibility that people with dyslexia do not adequately handle the context-dependent variation that speech signals typically contain. A mathematical model simulating such a sensitivity deficit mimics the speech-perception deficits attributed to dyslexia. To assess the nature of the dyslexic problem, the authors examined whether children with dyslexia handle context dependencies in speech differently than do normal-reading individuals. Contrary to the initial hypothesis, children with dyslexia did not show less context sensitivity in speech perception than did normal-reading individuals at auditory, phonetic, and phonological levels of processing, nor did they reveal any categorization deficit. Instead, intrinsic properties of online phonological processes, not phonological representations per se, may be impaired in dyslexia.

Improving language and literacy is a matter of time

Developmental deficits that affect speech perception increase the risk of language and literacy problems, which can lead to lowered academic and occupational accomplishment. Normal development and disorders of speech perception have both been linked to temporospectral auditory processing speed. Understanding the role of dynamic auditory processing in speech perception and language comprehension has led to the development of neuroplasticity-based intervention strategies aimed at ameliorating language and literacy problems and their sequelae.

Motion-onset VEPs in dyslexia. Evidence for visual perceptual deficit

The magnocellular deficit theory is one of the prominent theories in dyslexia. However, recent studies have produced conflicting results. In order to assess the validity of this theory, 8 dyslexic children and 14 controls were examined with a motion-onset visual evoked potential (VEP) paradigm at three different velocities (2, 8, and 16 deg/s). VEP elicited by stationary gratings served as a control condition. Amplitudes of motion-onset VEP components (P100, P200) but not of the stationary VEP are significantly attenuated in dyslexic children. Further, there is an interaction of group and velocity for the P200 in the way that group differences are more pronounced for higher velocities than for lower velocities. These results support the hypothesis of an impairment of a specific magnocellular function in dyslexia.

P300 investigation of phoneme change detection in dyslexic adults

A specific impairment in phoneme awareness has been hypothesized as one of the current explanations for dyslexia. We examined attentional shifts towards phonological information as indexed by event-related potentials (ERPs) in normal readers and dyslexic adults. Participants performed a lexical decision task on spoken stimuli of which 80% started with a standard phoneme and 20% with a deviant phoneme. A P300 modulation was expected for deviants in control adults, indicating that the phonological change had been detected. A mild and right-lateralized P300 was observed for deviant stimuli in controls, but was absent in dyslexic adults. This result suggests that dyslexic adults fail to make shifts of attention to phonological cues in the same way that normal adult readers do.

Developmental Dyslexia and Specific Language Impairment: Same or Different?

Developmental dyslexia and specific language impairment (SLI) were for many years treated as distinct disorders but are now often regarded as different manifestations of the same underlying problem, differing only in severity or developmental stage. The merging of these categories has been motivated by the reconceptualization of dyslexia as a language disorder in which phonological processing is deficient. The authors argue that this focus underestimates the independent influence of semantic and syntactic deficits, which are widespread in SLI and which affect reading comprehension and impair attainment of fluent reading in adolescence. The authors suggest that 2 dimensions of impairment are needed to conceptualize the relationship between these disorders and to capture phenotypic features that are important for identifying neurobiologically and etiologically coherent subgroups.

Developmental dyslexia in different languages: Language-specific or universal?

Most of the research on developmental dyslexia comes from English-speaking countries. However, there is accumulating evidence that learning to read English is harder than learning to read other European orthographies (Seymour, Aro, & Erskine, 2003). These findings therefore suggest the need to determine whether the main English findings concerning dyslexia can be generalized to other European orthographies, all of which have less irregular spelling-to-sound correspondences than English. To do this, we conducted a study with German- and English-speaking children (n=149) in which we investigated a number of theoretically important marker effects of the reading process. The results clearly show that the similarities between dyslexic readers using different orthographies are far bigger than their differences. That is, dyslexics in both countries exhibit a reading speed deficit, a nonword reading deficit that is greater than their word reading deficit, and an extremely slow and serial phonological decoding mechanism. These problems were of similar size across orthographies and persisted even with respect to younger readers that were at the same reading level. Both groups showed that they could process larger orthographic units. However, the use of this information to supplement grapheme-phoneme decoding was not fully efficient for the English dyslexics.