Hemispheric, attentional, and processing speed factors in the treatment of developmental dyslexia

Aim of the study is to analyze the contributions of hemispheric, attentional, and processing speed factors to the effects of neuropsychological treatment of developmental dyslexia. Four groups of dyslexic children (M-type dyslexia) were treated over a period of four months. A first group (n = 9) underwent Bakker's Hemisphere-Specific Stimulation, with presentation of words in the right and left visual field. A second group (n = 7) received the same stimuli randomly in either visual hemifield. A third group (n = 8) received the same words presented centrally at fixation point. A fourth group (n = 6) received central stimuli with fixed presentation time (1500 ms). The children were tested before and after treatment on reading and spelling measures. All groups improved significantly after treatment on all variables. However, the group that was treated with centrally presented stimuli improved more than the other groups in spelling measures. A possible explanation is that rapid, simultaneous presentation to both hemispheres enhances interhemispheric exchange, which could produce an advantage in tasks requiring a high degree of integration between left and right hemispheric functions, such as spelling. The absence of significant differences in reading improvement may point to the role of memory functions or strategic factors characterizing all the treatment programs, possibly overweighing the effect of the other factors.     

发展性阅读障碍的视觉空间注意加工能力

鉴于阅读起始于基础视觉加工阶段, 越来越多的研究者开始关注阅读障碍者的视觉空间注意加工能力。视觉空间注意是指个体对视觉刺激的空间位置的注意, 可通过线索提示、视觉搜索和视觉注意广度等视觉任务来考察。大量国内外研究发现, 发展性阅读障碍者在视觉空间注意任务下表现出行为和神经活动方面的异常。其中的神经机制问题不仅反映在与视觉空间注意有关的顶叶区域激活异常, 还存在于脑区间功能连接异常(如顶叶区域与字形加工区的功能连接)。未来研究还需利用横断和追踪研究探讨阅读障碍与视觉空间注意能力发展关系的内在机制, 以及探究语言特性对阅读障碍者视觉空间注意缺陷的可能调节作用。     

Developmental surface dyslexia and dysgraphia: An orthographic processing impairment

This study presents a detailed investigation of a young man in his early twenties who has suffered from a severe spelling impairment since childhood, and currently has a spelling age of only 9 years and 2 months. In contrast with the developmental phonological dyslexics reported by Campbell and Butterworth (1985) and Funnell and Davison (1989), his performance on tests of phonological awareness is good. In addition, he can read and spell non-words competently and, unlike normal 9-year-old children, virtually all of his spelling errors are phonologically appropriate. Further analysis of these errors reveals that he has knowledge of many of the different ways in which a given phoneme can be written, and that he uses phoneme-to-grapheme correspondences at the end of a word that are different from those he uses earlier in a word. However, he finds it difficult to spell words that contain uncommon phoneme-to-grapheme correspondences, which is compatible with the view that he has not developed an orthographic spelling lexicon. Although his oral reading of words is prompt and generally accurate, analysis of his lexical decision performance and the way that he defines homophones indicate that he does not have fully specified lexical entries available for reading either. We suggest that he suffers from a general orthographic processing deficit, and relies instead upon the combination of sub-lexical phonology and a lexicon that contains only partial information about way in which words are spelt. This leads to reasonably competent reading, even of many irregular words, but produces very poor spelling. It is argued that qualitatively different types of developmental dyslexia do genuinely exist, but that reading impairments are likely to be much more pronounced in children who have a phonological rather than an orthographic processing deficit.     

发展性阅读障碍的听觉时间加工缺陷

发展性阅读障碍是指个体在智力正常并且不缺乏学校教育的情况下, 仍无法获得与年龄相匹配的阅读技能的一种学习障碍, 其缺陷的本质一直是研究者争论的焦点。大量研究显示, 阅读障碍者常表现出听觉时间加工损伤。在行为层面, 阅读障碍者难以辨别快速、连续呈现刺激的顺序以及刺激本身的动态时间特征。在神经层面, 阅读障碍者诱发的失匹配负波更弱且具有异常的神经同步加工。这些损伤同时存在于对言语和非言语刺激的加工中, 表明听觉时间加工缺陷非言语加工所特有。未来的研究还需阐明以下几个问题：1)阅读障碍的听觉时间加工缺陷发生在哪些时间窗口, 随年龄增长如何变化; 2)阅读障碍听觉时间加工缺陷在神经层面的时间进程是怎样的; 3)听觉时间加工缺陷是否为阅读障碍的核心缺陷。     

Speed of phonological and orthographic processing as factors in dyslexia: electrophysiological evidence

The author investigated the hypothesis that speed of processing in the phonological and orthographic systems is one of the underlying variables of word-reading effectiveness. Speed of processing was assessed using measures of behavioral reaction time and electrophysiological latencies during phonological and orthographic task performance. Participants were 20 dyslexic and 20 normal-reading, male college students. An electrophysiological component complex (N1-P2-N2), as well as 2 other components (P3 and N4), was identified in both groups on each of the experimental tasks. Significant group differences were obtained only on the phonological tasks. Speed of processing during phonological judgment tasks was significantly prolonged among the dyslexic readers compared with the controls as reflected by P2, P3, and N4 latencies and reaction time. Between-task comparisons revealed significantly prolonged P2, P3, and N4 latencies on phonological compared with orthographic tasks in both dyslexic and normal readers, indicating that phonological classification of words may demand more time than orthographic classification. However, the gap score between speed of processing on the phonological and orthographic tasks was larger among the dyslexic readers and was observed mainly in P3 latency and reaction time. The highest correlation between word-reading accuracy score and the experimental measures was obtained in the dyslexic group with P3 latency gap score and in the control group with P2 latency gap score. The author proposes that slow phonological processing may cause "asynchrony" between the processing speeds within and between phonological and orthographic systems and may lead to a lack of efficient integration among the various subprocesses activated in reading, may slow down reading rate, and may impair word-reading effectiveness.     

Auditory processing in developmental dyslexia: An exploratory study of an auditory and visual matching training program with Swedish children with developmental dyslexia

This study examined whether training using a nonverbal auditory-visual matching task had a remedial effect on reading skills in developmental dyslexia. The pretest/post-test design was used with Swedish children ( N = 41), between the ages of 7 and 12. Training comprised twice-weekly sessions of 15 minutes, over eight weeks. There was an improvement in auditory-visual matching during the training period. There were also improvements in some reading test scores, especially in reading nonsense words and in reading speed. These improvements in tasks which are thought to rely on phonological processing suggest that such reading difficulties in dyslexia may stem in part from more basic perceptual difficulties, including those required to manage the visual and auditory components of the decoding task. The utility of the concept of auditory structuring is discussed in relation to auditory and phonological processing skills when a child learns to read.     

The processing of rhythmic structures in music and prosody by children with developmental dyslexia and developmental language disorder

Rhythm perception seems to be crucial to language development. Many studies have shown that children with developmental dyslexia and developmental language disorder have difficulties in processing rhythmic structures. In this study, we investigated the relationships between prosody and musical processing in Italian children with typical and atypical development. The tasks aimed to reproduce linguistic prosodic structures through musical sequences, offering a direct comparison between the two domains without violating the specificities of each one. About 16 Typically Developing children, 16 children with a diagnosis of Developmental Dyslexia, and 16 with a diagnosis of developmental language disorder (age 10–13 years) participated in the experimental study. Three tasks were administered: an association task between a sentence and its humming version, a stress discrimination task (between couples of sounds reproducing the intonation of Italian trisyllabic words), and an association task between trisyllabic nonwords with different stress position and three‐notes musical sequences with different musical stress. Children with developmental language disorder perform significantly lower than Typically Developing children on the humming test. By contrast, children with developmental dyslexia are significantly slower than TD in associating nonwords with musical sequences. Accuracy and speed in the experimental tests correlate with metaphonological, language, and word reading scores. Theoretical and clinical implications are discussed within a multidimensional model of neurodevelopmental disorders including prosodic and rhythmic skills at word and sentence level.     

The developmental course of processing speed in children with and without learning disabilities

This study contrasted the development of processing speed in children with and without learning disabilities. We examined whether the same global mechanism presumed to be responsible for the normal developmental improvement in processing speed might also be associated with the processing speed deficiencies observed in children with learning impairments. One hundred and twenty-two children with learning disabilities in reading and/or math and 206 non-disabled community controls participated. There were no differences in relation of age to the development of processing speed for children with and without learning disabilities. We interpreted these results as suggesting that the underlying etiologies for the normal developmental change in processing speed and for the relative deficiencies in processing speed seen among children with learning disabilities were different.     

When phonology fails: orthographic neighbourhood effects in dyslexia

Both cerebral hemispheres contain phonological, orthographic and semantic representations of words, however there are between-hemisphere differences in the relative engagement and specialization of the different representations. Taking orthographic processing for example, previous studies suggest that orthographic neighbourhood size (N) has facilitatory effects in the right but not the left hemispheres. To pursue the nature of this asymmetric N effect, in particular whether there are individual differences in such specialisation, we examined N in a case of developmental dyslexia, FM. We first describe the nature of his difficulties, which are mainly severe phonological deficits. Employing the divided visual field paradigm with FM revealed a greater sensitivity in the right than in the left hemisphere to orthographic variables, with a significant inhibitory N effect in the left, but not right hemisphere. Such inhibition, to a lesser degree, was found among a group of adults with dyslexia but not among age-matched normal readers. We argue that enhanced sensitivity to orthographic cues is developed in some cases of dyslexia when a normal, phonology-based left hemisphere word recognition processing is not achieved. The interpretation presented here is cast in terms of differences between people with dyslexia and typical readers that originate in the atypical way in which orthographic representations are initially set up.     

Factors affecting developmental changes in the speed of processing

Although many studies have found developmental changes in the speed of various processes, they have potentially confounded the subject's age with his knowledge of the task domain and use of strategies. In this study, the strategies used by the subject and his domain knowledge were independently assessed by a number of tasks. Subsequently, processing rate measures were obtained for a task (the “same/different” judgment task of simultaneously presented stimuli) in which domain knowledge was manipulated independently of age while controlling for strategy usage. It was found that the usual adult superiority in speed of processing could be markedly reduced if children possessed equivalent amounts of domain knowledge and this effect was domain specific. Further, it was found that differences in knowledge affected processing rates in both knowledgeable adults and children and to about the same extent. It was concluded that some part of the typical adult superiority in processing rate was due to knowledge differences.     

Acquired and developmental spelling dyslexia

Two cases of acquired spelling dyslexia and one case of developmental spelling dyslexia are described along with accounts of their performance on various psycholinguistic tasks. It is argued that there is some evidence that spelling dyslexia may exist in developmental form but that parallels are difficult to draw because of the very different histories of child and adult cases. It is also suggested that features of surface dyslexia exist in at least a proportion of spelling dyslexic cases and that this may be influenced by level of premorbid reading skill.     

Flicker masking and developmental dyslexia

Recent studies have provided evidence that dyslexic children tend to show longer visual persistence than control children when presented with low-spatial-frequency grating stimuli. The possibility that this phenomenon might reflect an impairment of inhibitory Y-cell activity in the visual system of dyslexics has been investigated. A flicker masking technique was used to mask Y-cell activity selectively in a group of dyslexic boys and a group of age-matched controls. There were no overall differences in reaction times to the offsets of grating patterns of various spatial frequencies between the groups, and no differences between subgroups defined by age, degree of reading impairment, or any other criterion. The results show no evidence of abnormal Y-cell function in developmental dyslexia.     

Phonemic deficits in developmental dyslexia

Summary The present study explored a possible relationship between reading difficulties and speech difficulties. Dyslexic and normal readers, matched for Reading Age, were compared first on a reading task and secondly on a speaking task.In the first experiment, the two groups were asked to read nonsense words aloud. Both groups were able to read one-syllable nonwords equally well but the dyslexics had more difficulty than the normal readers when asked to read two-syllable nonwords. Moreover, they found two-syllable nonwords containing consonant clusters particularly difficult. The probability of their making an error increased with the number of consonant clusters.In the second experiment, the subjects were required to repeat real words and nonsense words of two, three, or four syllables. Both groups found nonsense words more difficult to repeat than real words. However, the relative difficulty of nonsense words over real words was greater for the dyslexic group. Their difficulty was especially marked when they had to repeat four-syllable nonsense words.Thus, in both experiments the dyslexic readers were more affected by the phonological complexity of the stimuli than the normal readers were. Hence, it was suggested that the dyslexic readers tested were subject to a general phonemic deficit which affected their ability to process both written and spoken words.     

Action representation deficits in adolescents with developmental dyslexia

Developmental dyslexia (DD), a severe and frequent disorder of reading acquisition, is characterized by a diversity of cognitive and motor deficits whose interactions still remain under debate. Although deficits in the automatization of sensorimotor control have been highlighted, internal action representation allowing prediction has never before been investigated. In this study, we considered action representation of 18 adolescents with pure DD and 18 age-matched typical readers. Participants actually and mentally performed a visually guided pointing task involving strong spatiotemporal constraints (speed/accuracy trade-off paradigm). While actual and mental movement times of typical readers were isochronous and both conformed to Fitts’ law, the movement times of dyslexics differed between conditions, and only the actual movement times conformed to Fitts’ law. Furthermore, the quality of motor imagery correlated with word reading abilities. This suggests that the process of action representation is impaired in pure DD and supports the sensorimotor perspective of DD. Theoretical implications are discussed.     

Visual processing and dyslexia

Magnocellular-pathway deficits have been hypothesized to be responsible for the problems experienced by dyslexic individuals in reading. However, research has yet to provide a detailed account of the consequences of these deficits or to identify the behavioural link between them and reading disabilities. The aim of the present study was to determine the potential consequences of the magnocellular-pathway deficits for dyslexics in a comprehensive range of visual tasks. Dyslexics and nondyslexics were compared on their ability to (i) perform vernier-acuity and orientation-acuity tasks; (ii) perceive motion by using a range of measures common in the psychophysical literature (Dmin, Dmax, and global coherence); and (iii) perceive shapes presented in random-dot stereograms at a range of disparity pedestals, thereby dissociating stereopsis from vergence control. The results indicated no significant differences in performance between the dyslexic and nondyslexic subjects in terms of the visual-acuity measures. In general, dyslexics performed relatively poorly on measures of motion perception and stereopsis, although when considered individually some of the dyslexics performed better than some of the controls. The poor performance of the dyslexics in the stereo-gram tasks was attributable to a subgroup of dyslexics who also appeared to have severe difficulty with the motion-coherence task. These data are consistent with previous evidence that some dyslexics may have deficits within the magnocellular visual pathway.     

汉语发展性阅读障碍儿童视觉同时性加工技能子成分的发展及其与阅读的关系

通过分别以高频汉字(实验1)和图形非言语材料(实验2)为刺激的两个联合视觉注意任务, 并采用基于Budensen视觉注意理论的参数估计方法, 系统地探查小学三~六年级汉语发展性阅读障碍儿童的视觉同时性加工技能缺陷的内在机制。以43名汉语发展性阅读障碍儿童和46名生理年龄匹配典型发展儿童为被试, 每类被试均被分为小学中年级组(三、四年级)和高年级组(五、六年级)。两个实验均发现不同年级组的阅读障碍儿童在知觉加工速度参数上显著小于控制组儿童。在空间注意分布权重参数上, 实验1的结果显示, 不同于控制组儿童向左侧化发展的注意分布模式, 两个年级组的阅读障碍儿童均表现为无偏的注意分布; 而实验2未发现显著组别差异。且这两种同时性加工子技能分别与不同水平的汉语阅读技能密切相关。结果表明, 汉语阅读障碍儿童在同时加工多个视觉刺激时存在持续的知觉加工速度缓慢的问题, 在同时加工言语类刺激时还表现出异常的空间注意分布模式。本研究有助于从基础认知层面揭示汉语发展性阅读障碍儿童的缺陷机理, 为进一步设计相关的提高阅读效率的干预方案提供理论依据。     

Global and local pitch perception in children with developmental dyslexia

This study investigated global versus local pitch pattern perception in children with dyslexia aged between 8 and 11 years. Children listened to two consecutive 4-tone pitch sequences while performing a same/different task. On the different trials, sequences either preserved the contour (local condition) or they violated the contour (global condition). Compared to normally developing children, dyslexics showed robust pitch perception deficits in the local but not the global condition. This finding was replicated in a simple pitch direction task, which minimizes sequencing and short term memory. Results are consistent with a left-hemisphere deficit in dyslexia because local pitch changes are supposedly processed by the left hemisphere, whereas global pitch changes are processed by the right hemisphere. The present data suggest a link between impaired pitch processing and abnormal phonological development in children with dyslexia, which makes pitch pattern processing a potent tool for early diagnosis and remediation of dyslexia.     

Working memory functioning in developmental dyslexia

Working memory impairments in dyslexia are well documented. However, research has mostly been limited to the phonological domain, a modality in which people with dyslexia have a range of problems. In this paper, 22 adult students with dyslexia and 22 age- and IQ-matched controls were presented with both verbal and visuospatial working memory tasks. Performance was compared on measures of simple span, complex span (requiring both storage and processing), and dynamic memory updating in the two domains. The dyslexic group had significantly lower spans than the controls on all the verbal tasks, both simple and complex, and also on the spatial complex span measure. Impairments remained on the complex span measures after controlling statistically for simple span performance, suggesting a central executive impairment in dyslexia. The novelty of task demands on the initial trials of the spatial updating task also proved more problematic for the dyslexic than control participants. The results are interpreted in terms of extant theories of dyslexia. The possibility of a supervisory attentional system deficit in dyslexia is also raised. It seems clear that working memory difficulties in dyslexia extend into adulthood, can affect performance in both the phonological and visuospatial modalities, and implicate central executive dysfunction, in addition to problems with storage.     

Working memory functioning in developmental dyslexia

Working memory impairments in dyslexia are well documented. However, research has mostly been limited to the phonological domain, a modality in which people with dyslexia have a range of problems. In this paper, 22 adult students with dyslexia and 22 age- and IQ-matched controls were presented with both verbal and visuospatial working memory tasks. Performance was compared on measures of simple span, complex span (requiring both storage and processing), and dynamic memory updating in the two domains. The dyslexic group had significantly lower spans than the controls on all the verbal tasks, both simple and complex, and also on the spatial complex span measure. Impairments remained on the complex span measures after controlling statistically for simple span performance, suggesting a central executive impairment in dyslexia. The novelty of task demands on the initial trials of the spatial updating task also proved more problematic for the dyslexic than control participants. The results are interpreted in terms of extant theories of dyslexia. The possibility of a supervisory attentional system deficit in dyslexia is also raised. It seems clear that working memory difficulties in dyslexia extend into adulthood, can affect performance in both the phonological and visuospatial modalities, and implicate central executive dysfunction, in addition to problems with storage.