The sensory basis of reading problems

Spatial and temporal processing difficulties in Chinese children with developmental dyslexia: An ERP study

Magnocellular (M) deficit theory indicates that individuals with developmental dyslexia (DD) have low sensitivity to stimuli with high temporal frequencies (HTF) and low spatial frequencies (LSF). However, some studies found that temporal processing and spatial processing were correlated with different reading-related skills. Chinese is a logographic language, and visual skills are particularly important for reading in Chinese. It is necessary to investigate the temporal and spatial processing abilities in the M pathway of Chinese children with DD. Using electrophysiological recordings, the present study examined the mean amplitude and latency of P1 during a grating direction judgment task in 13 children with DD and 13 age-matched normal children. Dyslexic children showed a low amplitude and long latency of P1 in the HTF condition and LSF condition compared with age-matched children. In the HTF condition, the amplitude of P1 correlated with phonological awareness, and the latency of P1 correlated with reading fluency and rapid naming of digits. The amplitude of P1 in the LSF condition correlated with reading accuracy. This result suggested that Chinese children with DD had difficulties in both temporal and spatial processing in the M pathway. However, temporal processing and spatial processing played different roles in Chinese reading.

The association between reading abilities and visual-spatial attention in Hong Kong Chinese children

A growing body of research suggests that visual-spatial attention is important for reading achievement. However, few studies have been conducted in non-alphabetic orthographies. This study extended the current research to reading development in Chinese, a logographic writing system known for its visual complexity. Eighty Hong Kong Chinese children were selected and divided into poor reader and typical reader groups, based on their performance on the measures of reading fluency, Chinese character reading, and reading comprehension. The poor and typical readers were matched on age and nonverbal intelligence. A Posner's spatial cueing task was adopted to measure the exogenous and endogenous orienting of visual-spatial attention. Although the typical readers showed the cueing effect in the central cue condition (i.e., responses to targets following valid cues were faster than those to targets following invalid cues), the poor readers did not respond differently in valid and invalid conditions, suggesting an impairment of the endogenous orienting of attention. The two groups, however, showed a similar cueing effect in the peripheral cue condition, indicating intact exogenous orienting in the poor readers. These findings generally supported a link between the orienting of covert attention and Chinese reading, providing evidence for the attentional-deficit theory of dyslexia.

Visual Attention Processes and Oculomotor Control in Autism Spectrum Disorder: A Brief Review and Future Directions

Autism spectrum disorder (ASD) is defined as persistent deficits in social communication and social interaction, and restricted, repetitive patterns of behavior, interests or activities Diagnostic and Statistical Manual of Mental Disorders (5th ed., DSM-5; American Psychiatric Association, 2013). However, individuals with ASD show clearly atypical visual patterns. So far, indications of abnormal visual attention and oculomotor control concerning stimuli independent of social function in ASD have been found. The same findings have been shown in individuals suffering of other neurodevelopmental disorders (e.g., developmental coordination disorder and developmental dyslexia [DD]). Furthermore, visual attention processes and oculomotor control are supposed to be subserved by the magnocellular visual system, which has been found, in turn, to be dysfunctional in ASD and other neurodevelopmental disabilities (i.e., DD). The purpose of this article is to briefly review the link between oculomotor control and visual attention processes and ASD, and to discuss the specificity and overlap of eye movement findings between ASD and other neurodevelopmental disorders.

Are We Yet Able to Hear the Signal Through the Noise? A Comprehensive Review of Central Auditory Processing Disorders: Issues of Research and Practice

A Central Auditory Processing Disorder (CAPD) exists when a child has apparent difficulty in processing auditory information while possessing normal hearing. CAPD has been implicated by some as the root disorder underlying learning disabilities, Attention Deficit/Hyperactivity Disorder, and Specific Language Impairment. Despite years of research there is little consensus on a definition, criteria for assessment and diagnosis, and the efficacy of remediation and management. This comprehensive review of the CAPD literature examines the prevalence and etiology, assessment methods, differential diagnosis, as wVell as methods of management and remediation. Particular attention is paid to the details of research design and psychometrics. Support for the distinct existence of CAPD would be aided by the development of a modality-specific operational definition, assessment tools that were better standardized and normed, and the use of better control conditions in research.

The phonological mistake and 5D paradigm

In the first part of this article I present a background in scientific studies on dyslexia, from cognitive science to the neuropedagogical perspective. In this investigation the analysis of mental processes is the most important thanks to comparison with genetic research. In the second part, the dyslexic condition is seen from the perspective of the neuro-motor approach, named the Praxic Motor Theory, which improves neural circuits and inter-hemispherical exchange, electrical transmission and evoked potentials.<br /> In this perspective, the dyslexia condition is a disorder related to lack of coordination, including disorganization in space-time and lateral dominance. The phonological hypothesis referring to a lack of sign-sound association in dyslexia is inappropriate, as the term phonology has been intended in English literature as a more complex process and not simply an association between phoneme and grapheme. It is related to access to the word, groups of sounds, rather than single sounds. In this sense the dyslexic reader does not make a phonological mistake in terms of association, but a kinetic-motor one, in space-time from left to right.

Intracerebral functional connectivity-guided neurofeedback as a putative rehabilitative intervention for ameliorating auditory-related dysfunctions

Electroencephalography (EEG) constitutes one of the most eligible candidates for neurofeedback applications, principally due to its excellent temporal resolution best reflecting the natural dynamics of brain processes. In addition, EEG is easy to use and provides the opportunity for mobile applications. In the present opinion article, we pinpoint the advantages of using intracerebral functional connectivity (IFC) instead of quantitative scalp EEG for interventional applications. In fact, due to the convergence of multiple signals originating from different spatial locations and electrophysiological interactions, miscellaneous scalp signals are too unspecific for therapeutic neurofeedback applications. Otherwise, IFC opens novel perspectives for influencing brain activity in specific dysfunctional small- and large-scale neuronal networks with a reasonable spatial resolution. In the present article, we propose concrete interventional IFC applications that may be used to ameliorate auditory-related dysfunctions such as developmental dyslexia.

The validity and reliability of the Arabic Infant/Toddler Sensory Profile

In this study, we report the translation process, validity, and reliability of the Arabic Infant/Toddler Sensory Profile (IT_SP). A multistep approach was implemented to ensure the accuracy and equivalency of the Arabic and original English IT_SP. Factor analysis indicated that item loadings for over 50% of the items on the Arabic version were identical to the English version; all but three items had logical loadings. Intraclass correlation coefficients (ICC) between scores on the Arabic and English versions reported by parents who were bilingual were >.90 supporting bilingual validity. Alpha coefficients for each section varied from .40 to .74, which was within the range of the English version (.17 to .86), and were thus similar. ICCs between scores for repeated assessments varied from .81 to .99 supporting test-retest reliability. The results support the validity and reliability of the Arabic IT_SP.

Late, not early mismatch responses to changes in frequency are reduced or deviant in children with dyslexia: an event-related potential study

BACKGROUND

Developmental disorders of oral and written language have been linked to deficits in the processing of auditory information. However, findings have been inconsistent, both for behavioural and electrophysiological measures.

METHODS

In this study, we examined event-related potentials (ERPs) in 20 6- to 14-year-old children with developmental dyslexia and 20 age-matched controls, divided into younger (6-11 years, n = 10) and older (11-14 years, n = 10) age bands. We focused on early (mismatch negativity; MMN) and late (late discriminative negativity; LDN) conventional mismatch responses and associated measures derived from time-frequency analysis (inter-trial coherence and event-related spectral perturbation). Responses were elicited using an auditory oddball task, whereby a stream of 1000-Hz standards was interspersed with rare large (1,200 Hz) and small (1,030 Hz) frequency deviants.

RESULTS

Conventional analyses revealed no significant differences between groups in the size of the MMN to either large or small frequency deviants. However, the younger age band of children with dyslexia showed an enhanced inter-trial coherence in the theta frequency band over the time window corresponding to the MMN to small deviants. By contrast, these same children showed a reduced-amplitude LDN for the small deviants relative to their age-matched controls, whilst the older children with dyslexia showed a shorter and less intense period of event-related desynchronization over this time window.

CONCLUSIONS

Initial detection and discrimination of auditory frequency change appears normal or even enhanced in children with dyslexia. Rather, deficits in late-stage auditory processing appear to be a feature of this population.

Neural correlates of language and non-language visuospatial processing in adolescents with reading disability

Despite anecdotal evidence of relative visuospatial processing strengths in individuals with reading disability (RD), only a few studies have assessed the presence or the extent of these putative strengths. The current study examined the cognitive and neural bases of visuospatial processing abilities in adolescents with RD relative to typically developing (TD) peers. Using both cognitive tasks and functional magnetic resonance imaging (fMRI) we contrasted printed word recognition with non-language visuospatial processing tasks. Behaviorally, lower reading skill was related to a visuospatial processing advantage (shorter latencies and equivalent accuracy) on a geometric figure processing task, similar to findings shown in two published studies. FMRI analyses revealed key group by task interactions in patterns of cortical and subcortical activation, particularly in frontostriatal networks, and in the distributions of right and left hemisphere activation on the two tasks. The results are discussed in terms of a possible neural tradeoff in visuospatial processing in RD.

I can read it in your eyes: what eye movements tell us about visuo-attentional processes in developmental dyslexia

Most studies today agree about the link between visual-attention and oculomotor control during reading: attention seems to affect saccadic programming, that is, the position where the eyes land in a word. Moreover, recent studies show that visuo-attentional processes are strictly linked to normal and impaired reading. In particular, a large body of research has found evidence of defective visuo-attentional processes in dyslexics. What do eye movements tell us about visuo-attentional deficits in developmental dyslexia? The purpose of this paper is to explore the link between oculomotor control and dyslexia, taking into account its heterogeneous manifestation and comorbidity. Clinical perspectives in the use of the eye-movements approach to better explore and understand reading impairments are discussed.

Magno and parvo stimuli affect illusory directional hearing in normal and dyslexic readers

In an experimental paradigm adapted from Hari (1995), forty observers listened via headphones to 8 binaural clicks: 4 left-ear leading followed by 4 right-ear leading with either 38 or 140 ms interstimulus intervals (ISIs). Concurrently, they viewed either foveal or peripheral visual stimuli designed to activate either the parvocellular or magnocellular pathway. They then reported the perceived location of each click-pair. Our results replicated Hari's finding that observers mistake the perceived location of short ISI click-pairs more often than long. That is, when ISIs were short, the sounds seemed to play across the inside of the head in a phenomenon called illusory directional hearing. However, when click-pairs were accompanied by peripheral visual stimuli that activated the magnocellular pathway, observers were more accurate than when there were no visual stimuli. Conversely, parvocellular-activating foveal visual stimuli produced more illusory hearing than when there were no visual stimuli. These findings suggest that activating the slow sustained parvocellular system may result in a longer processing window. Thirty dyslexic observers who repeated the experimental paradigm had an even longer processing window than control observers indicating that dyslexics may have a magnocellular system deficit.

Inflectional spelling deficits in developmental dyslexia

The goal of this study was to examine past-tense spelling deficits in developmental dyslexia and their relationship to phonological abilities, spoken morphological awareness and word specific orthographic memory. Three groups of children (28 9-year-old dyslexic, 28 chronological age-matched and 28 reading/spelling age-matched children) completed a battery of tests including spelling regularly inflected words (e.g., kissed) and matched one-morpheme words (e.g., wrist). They were also assessed on a range of tests of reading and spelling abilities and associated linguistic measures. Dyslexic children were impaired in relation to chronological age-matched controls on all measures. Furthermore, they were significantly poorer than younger reading and spelling age-matched controls at spelling inflected verbs, supporting the existence of a specific deficit in past-tense spelling in dyslexia. In addition to under-using the -ed spelling on inflected verbs, the dyslexic children were less likely to erroneously apply this spelling to one-morpheme words than younger controls. Dyslexics were also poorer than younger controls at using a consistent spelling for stems presented in isolation versus as part of an inflected word, indicating that they make less use of the morphological relations between words to support their spelling. In line with this interpretation, regression analyses revealed another qualitative difference between the spelling and reading age-matched group and the dyslexic group: while both spoken morphological awareness and orthographic word specific memory were significant predictors of the accuracy of past-tense spelling in the former group, only orthographic memory (irregular word reading and spelling) was a significant factor in the dyslexic group. Finally, we identified a subgroup of seven dyslexic children who were severely deficient in past-tense spelling. This subgroup was also significantly worse than other dyslexics and than younger controls on scores of orthographic memory. The implications of our findings for teaching and remediation strategies are discussed.

Hemispheric asymmetry profiles during beginning reading: effects of reading level and word type

We evaluated how right- and the left-temporal lobe activation of first (1(st) LR), second (2(nd)LR), and third (3(rd)LR) level readers (N = 60; Age = 6-9 years) varied with reading level, word characteristics, and cognitive abilities by using electroencephalogram measurements while the children read high-frequency/high-imageability, high-frequency/low-imageability, and nonsense words. The ANOVA showed significant interaction effects: 1(st)LR had greater right-hemispheric activation than 3(rd)LR, who had greater left-hemispheric activation; for nonsense words, 1(st)LR had lower left-hemisphere activation than that of 2(nd)LR and 3(rd)LR. The electroencephalogram (EEG) measure of hemispheric asymmetry indicated a developmental effect on lateralized activity in the temporal lobes of beginning readers during word reading.

Dyslexic participants show intact spontaneous categorization processes

We examine the performance of dyslexic participants on an unsupervised categorization task against that of matched non-dyslexic control participants. Unsupervised categorization is a cognitive process critical for conceptual development. Existing research in dyslexia has emphasized perceptual tasks and supervised categorization tasks (for which intact attentional processes are paramount), but there have been no studies on unsupervised categorization. Our investigation was based on Pothos and Chater's (Cognit. Sci., 2002; 26: 303-343) model of unsupervised categorization and the corresponding methodology for analysing results. Across all performance indices and various data-processing options, we could identify no difference between dyslexic and non-dyslexic participants.

Sensitivity to visual and auditory stimuli in children with developmental dyslexia

This study considered the extent to which 23 children with dyslexia differed from 23 reading age (RA) and 23 chronological age (CA) matched controls in their ability to make temporal judgements about auditory and visual sequences of stimuli, and in the speed of their reactions to the onsets and offsets of visual and auditory stimuli. The children with dyslexia were slower (p = 0.039) than the CA controls in their reactions to non-verbal auditory onsets (tones), were less able to recognize the first stimulus of a sequence of tones (p = 0.022), and were less accurate in identifying the initial phoneme of a sequence of three (p < 0.001). These characteristics may be manifestations of an impaired temporal processing system for rapid auditory stimuli. CA controls responded more quickly to tone onsets than to tone offsets (p = 0.025), but the dyslexic and RA groups showed no significant difference (p > 0.05) in their reaction times to onsets and offsets of these non-verbal auditory stimuli. Dyslexic readers showed impairment compared with CA controls in responding to the last of a sequence of three non-verbal visual stimuli (shapes), p = 0.02. Reaction times in the visual and auditory onset and offset tasks were richly intercorrelated in the control groups, but the dyslexic group did not show as many significant correlations in reaction times between the auditory and visual domains, or between the onset and offset RTs within each modality. These results suggest that there may be a less integrated cross-modal and intra-modal temporal system in children with dyslexia than in controls. In many of the measures in this study, the performance of the dyslexic group resembled that of the RA control group but differed from CA controls, which implies a developmental delay. The possibility that such a cognitive delay may be related to an underlying neurological disorder is discussed.

Auditory event-related potentials differ in dyslexics even when auditory psychophysical performance is normal

Developmental dyslexia is characterized by a phonological processing deficit and impaired low-level auditory processing may contribute to this problem. However, this remains controversial because not all dyslexic individuals show psychophysical deficits on auditory processing tasks; hence it has been argued that auditory processing deficits are not a causal factor in dyslexia. Because behavioral psychophysical tasks include both bottom-up processing and top-down strategies, dyslexics' successful coping strategies may positively influence their performance on auditory behavioral measures. Therefore we have studied whether dyslexics who perform adequately on auditory psychophysical tasks nevertheless show electrophysiological evidence of impaired auditory processing. We compared auditory event-related mismatch negativity (MMN) potentials to frequency modulated (FM) tones at 5, 20 and 240 Hz between dyslexic adults and controls. Groups were matched for age, cognitive ability and psychophysical FM detection thresholds. The dyslexic group showed significantly smaller MMNs in the 20 Hz FM condition in both the early (150-300 ms, P=0.010) and late (300-500 ms, P=0.049) time frames. A 2-way ANOVA showed a significant group by FM rate interaction (P=0.012). There were no significant differences between the groups in the 5 Hz or 240 Hz conditions. The magnitude of the 20 Hz FM MMN correlated with the degree of discrepancy between cognitive and literacy skills (0.66, P=0.003) in the entire group. Thus, even among compensated dyslexics with above-average cognitive abilities and adequate performance on auditory psychophysical tasks, the MMN responses of some dyslexic adults were found to be abnormal.

Temporal order judgment in dyslexia

Hari et al. (Brain 174:1373-1380, 2001) demonstrated that dyslexics showed a sluggish attention capture in both visual hemifields. Additionally, they indicated a left-right asymmetry in the perception of temporal order of two visual stimuli (they performed worse than controls only if the stimulus in the left hemifield preceded that in right hemifield). They suggested that a left-sided minineglect is associated with dyslexia. We hypothesized that if a kind of neglect syndrome is responsible for the asymmetry they found, dyslexics should not only show a left-right asymmetry in temporal order judgment of two laterally presented stimuli but also perform equally well as controls when the stimuli are vertically aligned. Our results indicated that in both tasks dyslexics performed generally worse than normal readers. The results suggest that dyslexics suffer from a more general problem of order discrimination.

A processing speed deficit in dyslexic adults? Evidence from a peg-moving task

Developmental dyslexia is diagnosed when literacy skills are not commensurate with a person's general cognitive ability and education. While the most common difficulty found in dyslexia is poor phonological processing, many dyslexics are reported to be clumsy, with poor handwriting, suggesting that there may be a motor deficit in dyslexia. To establish whether the motor difficulties described in dyslexic children persist into adulthood, we tested 18 dyslexic adults and 22 control participants on Annett's peg-moving task. The dyslexic participants performed significantly slower than control adults on the peg-moving task with their dominant hands (p=0.004). Furthermore, response times (RTs) during tasks testing component literacy skills correlated with peg-moving ability in the dominant hand in the entire group (orthographic r=0.448, p=0.005; phonological r=0.383, p=0.025). These results indicate that a motor speed deficit in dyslexia may not be simply a sign of developmental delay, but may persist into adulthood. Furthermore, motor speed may be related to the speed at which literacy information is processed.

Developmental dyslexia in a regular orthography: a single case study

This study of an adult case examined in detail with eye movement measures the reading speed problem which is characteristic for developmental dyslexia in regular orthographies. A dramatic length effect was found for low frequency words and for pseudowords, but not for high frequency words. However, even for high frequency words it was found that reading times were substantially prolonged although number of fixations did not differ. A neurocognitive assessment revealed no visual deficits (parallel processing, precedence detection, coherent motion detection) but speed impairments for certain verbal and phonological processes. We propose that the reading difficulties are phonological in nature, but these difficulties become manifest as inefficiency and not as inability.

The effect of script on poor readers' sensitivity to dynamic visual stimuli

The current research examined performance of good and poor readers of Thai on two tasks that assess sensitivity to dynamic visual displays. Readers of Thai, a complex alphabetic script that nonetheless has a regular orthography, were chosen in order to contrast patterns of performance with readers of Korean Hangul (a similarly regular language but one that has a simple visual format, see ). Thai poor readers were less sensitive than good readers on the two measures of dynamic visual processing; they had higher thresholds for detecting coherent movement and required longer ISIs to report group movement in the Ternus task. These results differ from those for poor readers of Korean Hangul that found no relationship between visual processing thresholds and reading skill. This contrast suggests that the expression of visual processing problems in dyslexia is mediated by the format properties of the writing system and points to the need to consider such factors in formulating brain-behavior relationships.

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.

Sensory processing, reading, IQ, and attention

Detection thresholds for two visual- and two auditory-processing tasks were obtained for 73 children and young adults who varied broadly in reading ability. A reading-disabled subgroup had significantly higher thresholds than a normal-reading subgroup for the auditory tasks only. When analyzed across the whole group, the auditory tasks and one of the visual tasks, coherent motion detection, were significantly related to word reading. These effects were largely independent of ADHD ratings; however, none of these measures accounted for significant variance in word reading after controlling for full-scale IQ. In contrast, phoneme awareness, rapid naming, and nonword repetition each explained substantial, significant word reading variance after controlling for IQ, suggesting more specific roles for these oral language skills in the development of word reading.

Specific reading disability (dyslexia): what have we learned in the past four decades?

We summarize some of the most important findings from research evaluating the hypothesized causes of specific reading disability ('dyslexia') over the past four decades. After outlining components of reading ability, we discuss manifest causes of reading difficulties, in terms of deficiencies in component reading skills that might lead to such difficulties. The evidence suggests that inadequate facility in word identification due, in most cases, to more basic deficits in alphabetic coding is the basic cause of difficulties in learning to read. We next discuss hypothesized deficiencies in reading-related cognitive abilities as underlying causes of deficiencies in component reading skills. The evidence in these areas suggests that, in most cases, phonological skills deficiencies associated with phonological coding deficits are the probable causes of the disorder rather than visual, semantic, or syntactic deficits, although reading difficulties in some children may be associated with general language deficits. Hypothesized deficits in general learning abilities (e.g., attention, association learning, cross-modal transfer etc.) and low-level sensory deficits have weak validity as causal factors in specific reading disability. These inferences are, by and large, supported by research evaluating the biological foundations of dyslexia. Finally, evidence is presented in support of the idea that many poor readers are impaired because of inadequate instruction or other experiential factors. This does not mean that biological factors are not relevant, because the brain and environment interact to produce the neural networks that support reading acquisition. We conclude with a discussion of the clinical implications of the research findings, focusing on the need for enhanced instruction.

On the automaticity/cerebellar deficit hypothesis of dyslexia: balancing and continuous rapid naming in dyslexic and ADHD children

The present study examined the relationship of reading disability (RD) and attention deficit hyperactivity disorder (ADHD) to balancing problems. In the cerebellar deficit hypothesis of dyslexia of Nicolson et al. [Trends Neurosci. 24 (2001) 508], balancing problems are taken as sign of a cerebellar deficit and were found to be associated with dyslexia. Four groups of 10 children each, representing all combinations of RD (absent versus present) and ADHD (absent versus present), were included. However, poor balancing (assessed both singly and together with a secondary task) was not found to be associated with RD, but with ADHD. In contrast, poor performance on continuous rapid naming tasks (digit and color naming) was found to be associated with RD and not with ADHD.

Dyslexia: nature and nurture

This paper explores the balance of genetic and environmental influences on dyslexia in generally supportive educational environments. Evidence from family studies suggests and research with identical and fraternal twins confirms the presence of strong genetic influences on dyslexia, though the way dyslexia is defined influences the degree of genetic influence. The behavioural genetic evidence is supported with molecular genetic evidence from DNA analyses suggesting regions on several different chromosomes where genes related to dyslexia are likely to be found. The behavioural and molecular genetic analyses are also applied to different component word reading skills (orthographic coding and phonological decoding) as well as to related language skills (phoneme awareness) to better understand the genetic and cognitive pathways to dyslexia.