Neural substrates of impaired categorical perception of phonemes in adult dyslexics: an fMRI study

Phonological developmental dyslexics remain impaired in phonetic categorical perception (CP) even in adulthood. We studied the brain correlates of CP in dyslexics and controls using a block design fMRI protocol and stimuli from an phonetic continuum between natural /Pa/ and /Ta/ syllables. Subjects performed a pseudo-passive listening task which does not imply voluntary categorical judgment. In the control group, categorical deviant stimuli elicited specific activations in the left angular gyrus, the right inferior frontal gyrus and the right superior cingulate cortex. These regions were not activated in the dyslexic group in which activation was observed for acoustic but not phonetic changes in stimuli. Failures to activate key regions for language perception and auditory attention in dyslexic might account for persistent deficits in phonological awareness and reading tasks.     

Reaction times and dyslexia

Five groups of children, including two groups of dyslexics (aged 15 and 11 years), were tested on simple reaction, selective choice reaction, and lexical decision tasks. In simple reactions to a pure tone, the dyslexic children responded as quickly as their chronological age controls and significantly faster than their reading age controls. In selective choice reactions to pure tones, the dyslexic children were significantly impaired compared with their chronological age controls and no faster than their reading age controls. This speed impairment obtained even though a selective choice reaction task has only one positive response. In “by-item” analyses of lexical decisions to spoken words, the dyslexic children were significantly impaired compared even with their reading age controls. The pattern of results suggests that at least two factors contribute to slowness of dyslexic children: a general deficit reflected in slower stimulus classification speed and a linguistic deficit reflected in slower lexical access speed.     

Performance of dyslexic children on speech perception tests

Several researchers who have compared the performance of dyslexic and normal-reading children on a variety of different tasks have suggested that dyslexic children may have subtle deficits in the phonemic analysis of spoken as well as written language. Thus it is of interest to know how children who have extraordinary difficulty learning to read can perform explicity auditory-phonetic tasks. Seventeen dyslexic children (10 years of age) and a group of 17 controls were administered tests of identification and discrimination of synthesized voiced stop consonants differing in place of articulation. These were tests of the type used to study categorical perception in adults, adapted for use with young children. Significant differences between dyslexics and controls were found in both kinds of tasks; the pattern of identification and discrimination differences suggests an inconsistency in the dyslexics' phonetic classification of auditory cues. A significant relationship was found between reading level and speech discrimination.     

Identifying subtypes of reading disability in the Spanish language

This study was designed to examine the dyslexic subtypes in a transparent orthography (i.e., Spanish language). The subtyping procedure used comparison with chronological-age-matched and reading-level controls on reaction times (RTs) to high frequency words and to pseudowords. Using regression-based procedures, the authors identified 20 phonological and 48 surface dyslexics from a sample of 89 dyslexic third-grade children by comparing them to chronological-age-matched controls on RTs to high frequency and pseudoword reading. However, when the dyslexic subtypes were defined by reference to reading-level controls, the same 20 phonological dyslexics were defined, but only 19 surface dyslexics were identified. Nevertheless, the results of the phonological awareness tasks and error analysis do not validate the division of the dyslexic sample into these subgroups.     

Voluntary saccadic control in dyslexia

The role of eye-movement control in dyslexia is still unclear. Recent studies, however, confirmed that dyslexics show poor saccadic control in single and sequential target tasks. In the present study we investigated whether dyslexic subjects are impaired on an antisaccade task requiring saccades against the direction of a stimulus. Altogether, 620 subjects between the ages of 7 and 17 years were classified as dyslexics (N = 506) or control subjects (N = 114) on the grounds of the discrepancy between their intellectual abilities and reading/spelling achievements. All subjects performed an overlap prosaccade and a gap antisaccade task with 100 trials to each side of stimulation in random order. Variables analysed were the overall saccadic reaction time of both tasks; and from the antisaccade task the number of errors (prosaccades), the number of corrected errors, and the number of trials in which the subjects still failed to reach the side opposite the stimulus even after two saccades. An analysis of variance was carried out taking into account the development of saccadic behaviour with age and the differences between the groups. The results confirm development of saccade control with age, especially in the voluntary component (a frontal-lobe function) for both groups, but indicate that the antisaccade task performance, as measured by the error and the correction rate, is significantly worse in the dyslexic group at ages above 8 years. Up to 50% of the dyslexics performed the antisaccade task 1.5 standard deviations below the mean of the controls.     

Language deficits in dyslexic children: speech perception, phonology, and morphology

We investigated the relationship between dyslexia and three aspects of language: speech perception, phonology, and morphology. Reading and language tasks were administered to dyslexics aged 8-9 years and to two normal reader groups (age-matched and reading-level matched). Three dyslexic groups were identified: phonological dyslexics (PD), developmentally language impaired (LI), and globally delayed (delay-type dyslexics). The LI and PD groups exhibited similar patterns of reading impairment, attributed to low phonological skills. However, only the LI group showed clear speech perception deficits, suggesting that such deficits affect only a subset of dyslexics. Results also indicated phonological impairments in children whose speech perception was normal. Both the LI and the PD groups showed inflectional morphology difficulties, with the impairment being more severe in the LI group. The delay group's reading and language skills closely matched those of younger normal readers, suggesting these children had a general delay in reading and language skills, rather than a specific phonological impairment. The results are discussed in terms of models of word recognition and dyslexia.     

Using fMRI to study recovery from acquired dysphasia

We have used functional magnetic resonance imaging (fMRI) to characterize brain activations associated with two distinct language tasks performed by a 28-year-old woman after partial recovery from dysphasia due to a left frontal hemispheric ischemic stroke. MRI showed that her ischemic lesion extended posteriorly from the left inferior frontal to the perisylvian cortex. fMRI scans of both language tasks revealed substantial differences in activation pattern relative to controls. The nature of this difference was task-specific. During performance of a verbal semantic decision task, the patient, in contrast to controls, activated a network of brain areas that excluded the inferior frontal gyrus (in either hemisphere). A second task involving rhyme judgment was designed to place a heavier cognitive load on language production processes and activated the left inferior frontal gyrus (Broca's area) strongly in normal controls. During this task, the most prominent frontal activation in the patient occurred in the right homologue of Broca's area. Subsequent analysis of this data by methods able to deal with responses of changing amplitude revealed additional, less sustained recruitment by the patient of cortex adjacent to the infarct in the region inferior to Broca's area during rhyming. These results suggest that in addition to changes in cognitive strategy, recovery from dysphasia could be mediated by both the preservation of neuronal networks in and around the infarct and the use of homologous regions in the contralateral hemisphere.     

A comparison of word recognition processes in dyslexic and normal readers at two reading-age levels

This study addressed the question of whether dyslexic children use qualitatively different word identification processes as compared to normal readers at the same stage of reading acquisition. Fifty-two dyslexic children and reading-age matched normal readers were required to pronounce words and pseudowords designed to tap several word recognition and decoding processes. Performance profiles were compared for the two reading groups at two reading ages. Although an invariant acquisition sequence was observed across reading groups, differences in level of performance between dyslexics and reading-age controls varied as a function of reading age. The performance of the more advanced dyslexics was virtually indistinguishable from normal readers on all measures. In contrast, the younger reading age dyslexics differed from normal readers on several measures of spelling-sound correspondences. However, no reading group differences were observed on measures of word recognition. The results indicated that dyslexics and normal readers at the same reading age use essentially the same processes to recognize words, but may differ in knowledge of correspondence rules.     

Automatic Activation of Word Phonology from Print in Deep Dyslexia

The performance of deep dyslexics in oral reading and other tasks suggests that they are poor at activating the phonology of words and non-words from printed stimuli. As the tasks ordinarily used to test deep dyslexics require controlled processing, it is possible that the phonology of printed words can be better activated on an automatic basis. This study investigated this possibility by testing a deep dyslexic patient on a lexical decision task with pairs of stimuli presented simultaneously. In Experiment 1, which used content words as stimuli, the deep dyslexic, like normal subjects, showed faster reaction times on trials with rhyming, similarly spelled stimuli (e.g. bribe-tribe) than on control trials (consisting of non-rhyming, dissimilarly spelled words), but slower reaction times on trials with non-rhyming, similarly spelled stimuli (e.g. couch-touch). When the experiment was repeated using function words as stimuli, the patient no longer showed a phonological effect. Therefore, the phonological activation of printed content words by deep dyslexics may be better than would be expected on the basis of their oral reading performance.     

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.     

Spanish developmental dyslexia: Prevalence, cognitive profile, and home literacy experiences

This study was designed to examine the prevalence, cognitive profile, and home literacy experiences in subtypes of Spanish developmental dyslexia. The subtyping procedure used comparison with chronological-age-matched and reading-level controls on reaction times and accuracy responses to high-frequency words and pseudowords. Using regression-based procedures, 8 phonological dyslexics and 16 surface dyslexics were identified from a sample of 35 dyslexic fourth graders by comparing them with chronological-age-matched controls on reaction times to high-frequency word and pseudoword reading. However, when the dyslexic subtypes were defined by reference to reading-level controls, 12 phonological dyslexics were defined but only 5 surface dyslexics were identified. Both dyslexic subtypes showed a deficit in phonological awareness, but children with surface dyslexia also showed a deficit in orthographical processing assessed by a homophone comprehension task. This deficit was associated with poor home literacy experiences, with the group of parents with children matched in reading age, in comparison with the group of parents with children with surface dyslexia, reporting more literacy home experiences.     

Developmental and acquired dyslexia: A comparison

Jorm (1979a) has drawn attention to similarities between developmental dyslexia and acquired deep dyslexia, an analogy which has been criticized by A. W. Ellis (1979). A series of three experiments compared the two syndromes, using the techniques applied by Patterson and Marcel (1977) to adult deep dyslexics, to study a group of 15 boys suffering from developmental dyslexia. Patterson and Marcel's patients were able to perform a lexical decision task but showed no evidence of phonemic encoding of nonwords; our dyslexic children performed this task very slowly and with reduced accuracy but showed clear evidence of phonemic coding of the nonword items. Patterson and Marcel observed that their patients could not read out orthographically regular nonwords; our dyslexic children were able to do this task, although more slowly and somewhat less accurately than their chronological age or reading age controls. Finally, Patterson and Marcel observed that highly imageable words were more likely to be read correctly than words of equal frequency but low imageability; we observed a similar effect in both our dyslexic group and in their reading age controls. This implies that the imageability effect may not be peculiar to dyslexics but may be characteristic of normal reading under certain conditions. It is concluded that developmental dyslexics differ from the patients studied by Patterson and Marcel in demonstrating a pattern of reading which, though slow, is qualitatively similar to the reading of normal readers of a younger age. As such, our results do not support Jorm's position.     

An intrahemispheric integration deficit in dyslexia

In order to investigate the hypothesis that dyslexia may result from a failure of intrahemispheric integration between auditory-verbal and visual-verbal processing, a dichotic listening task and a parallel divided visual field task were administered to a group of dyslexic boys between the ages of 8 and 11 years, and a group of normal control subjects individually matched for age and WISC intelligence. The dyslexics were on average over two years retarded in reading and spelling. Dyslexics exhibited a normal right ear advantage on dichotic listening for digits although lesser right ear advantage was related to reading retardation. In the divided visual field task, the normal controls showed a left visual field advantage for digits which it is argued resulted from a failure in fixation linked to reading habits. Within the dyslexic group greater reading deficiency was associated with relative bilateralization for visual verbal processing. The results therefore support the hypothesis.     

Morphological Knowledge in Children with Dyslexia

The phonological skills are not the only linguistic abilities which are observed to have some influence on reading achievement in dyslexics. In addition to phonological skills, morphological skills should be also taken in consideration. The aim of this study is to extend investigation the linguistic abilities of children with dyslexia to the morphological level through examination whether there is a lack of morphological knowledge in children with dyslexia for Bosnian language with transparent orthography. Testing sample included 45 children with dyslexia that are compared with chronological age and reading level controls. The dyslexic children performed significantly worse than same age controls on all forms of word and the most complex word formation tasks. Based on the examination of standardized discriminant function coefficients the variable with the highest weight in defining the first discriminant function was the suffixal formation, declination of personal pronouns, changing gender of adjectives with regard to the gender of a noun, and changing of gender of cardinal numbers with regard to the gender of a noun best differentiates groups. Results of multivariate analyses of variance also showed that chronological age and reading level groups outperformed dyslexics on all these tasks. Our results suggest that dyslexics have problems with morphological knowledge which indicate that certain actions regarding the development of morphological abilities in dyslexics should be taken in the elementary grades.     

The role of sensorimotor impairments in dyslexia: a multiple case study of dyslexic children

This study attempts to investigate the role of sensorimotor impairments in the reading disability that characterizes dyslexia. Twenty-three children with dyslexia were compared to 22 control children, matched for age and non-verbal intelligence, on tasks assessing literacy as well as phonological, visual, auditory and motor abilities. The dyslexic group as a whole were significantly impaired on phonological, but not sensorimotor, tasks. Analysis of individual data suggests that the most common impairments were on phonological and visual stress tasks and the vast majority of dyslexics had one of these two impairments. Furthermore, phonological skill was able to account for variation in literacy skill, to the exclusion of all sensorimotor factors, while neither auditory nor motor skill predicted any variance in phonological skill. Visual stress seems to account for a small proportion of dyslexics, independently of the commonly reported phonological deficit. However, there is little evidence for a causal role of auditory, motor or other visual impairments.     

概化理论预算限制下最佳样本量估计

概化理论广泛应用于各种心理测评实践中。当有预算限制时,概化理论需要考虑如何设计一个测量可靠性相对较高且可行性也相对较强的测量程序,这就要求通过某些途径估计最佳样本量。拉格朗日乘法是概化理论预算限制下最佳样本量估计较为成熟的方法。探讨了概化理论预算限制下最佳样本量估计的一些影响因素,如受总预算舍入的影响等,也提出了一些后续改善的建议,如推导出拉格朗日乘法的统一公式等     

Automaticity: a new framework for dyslexia research?

The performance of a group of 23 13-year-old dyslexic children was compared with that of same-age controls on a battery of tests of motor balance. A dual-task paradigm was used--subjects performed each test twice, once as a single task, and once as a dual task concurrently with a secondary task. Two alternative secondary tasks were used, the classic counting-backwards task and an auditory choice reaction task. Both secondary tasks were calibrated for each subject to ensure that their performance on the secondary task alone fell between pre-specified performance criteria. In all single-task conditions there was no difference between the performance of the two groups. By contrast, in 19 out of the 20 tests performed under dual-task conditions, the dyslexic group were significantly impaired, whereas the controls showed no impairment, thus resulting in significantly better performance by the control group than the dyslexic group. The sole exception was that the dyslexic children were not impaired on the easiest balance condition with the choice reaction task. Under the dual-task conditions the dyslexic children also performed worse than the controls on the secondary task. It is very hard to accommodate the findings within the traditional framework of a deficit specific to lexical skills. One plausible explanation of the results is that, unlike the controls, the dyslexic children need to invest significant conscious resources for monitoring balance, and thus their performance is adversely affected by any secondary task which serves to distract attention from the primary task. This need for "conscious compensation" suggests that for dyslexic children the skill of motor balance is poorly automatized. It is possible, therefore, that many of the reading deficits of dyslexic children are merely symptoms of a more general learning deficit--the failure to fully automatize skills.     

Developmental dyslexia and widespread activation across the cerebellar hemispheres

Developmental dyslexia is the most common learning disability in school-aged children with an estimated incidence of five to ten percent. The cause and pathophysiological substrate of this developmental disorder is unclear. Recently, a possible involvement of the cerebellum in the pathogenesis of dyslexia has been postulated. In this study, 15 dyslexic children and 7 age-matched control subjects were investigated by means of functional neuroimaging (fMRI) using a noun-verb association paradigm. Comparison of activation patterns between dyslexic and control subjects revealed distinct and significant differences in cerebral and cerebellar activation. Control subjects showed bilaterally well-defined and focal activation patterns in the frontal and parietal lobes and the posterior regions of the cerebellar hemispheres. The dyslexic children, however, presented widespread and diffuse activations on the cerebral and cerebellar level. Cerebral activations were found in frontal, parietal, temporal and occipital regions. Activations in the cerebellum were found predominantly in the cerebellar cortex, including Crus I, Crus II, hemispheric lobule VI, VII and vermal lobules I, II, III, IV and VII. This preliminary study is the first to reveal a significant difference in cerebellar functioning between dyslexic children and controls during a semantic association task. As a result, we propose a new hypothesis regarding the pathophysiological mechanisms of developmental dyslexia. Given the sites of activation in the cerebellum in the dyslexic group, a defect of the intra-cerebellar distribution of activity is suspected, suggesting a disorder of the processing or transfer of information within the cerebellar cortex.     

Unilateral implicit motor learning deficit in developmental dyslexia

It has been suggested that developmental dyslexia involves various literacy, sensory, motor skill, and processing speed deficits. Some recent studies have shown that individuals with developmental dyslexia exhibit implicit motor learning deficits, which may be related to cerebellar functioning. However, previous studies on implicit motor learning in developmental dyslexics have produced conflicting results. Findings from cerebellar lesion patients have shown that patients' implicit motor learning performance varied when different hands were used to complete tasks. This suggests that dyslexia may have different effects on implicit motor learning between the two hands if cerebellar dysfunction is involved. To specify this question, we used a one-handed version of a serial reaction time task to compare the performance of 27 Chinese children with developmental dyslexics with another 27 age-matched children without reading difficulties. All the subjects were students from two primary schools, Grades 4 to 6. The results showed that children with developmental dyslexic responded more slowly than nondyslexic children, and exhibited no implicit motor learning in the condition of left-hand response. In contrast, there was no significant difference in reaction time between two groups of children when they used the right hand to respond. This finding indicates that children with developmental dyslexia exhibited normal motor skill and implicit motor learning ability provided the right hand was used. Taken together, these results suggested that Chinese children with developmental dyslexia exhibit unilateral deficits in motor skill and implicit motor learning in the left hand. Our findings lend partial support to the cerebellar deficit theory of developmental dyslexia.     

Learning orthography in adulthood: A magnetoencephalographic study

Previous work demonstrated that there were differences between literate and comparable illiterate adult subjects. These differences were found in the performance on several tests and on patterns of activation on PET and fMRI. In the present study subjects that learned to read and to write in adulthood (being previously completely illiterate) were compared to controls, that is subjects that learned at school at the proper age. Magnetoencephalography was done while subjects were reading words. Results showed that, although the reading performance was the same in both groups while performing the task, the pattern of source distribution was different between groups. There were more late sources in right temporo‐parietal areas of late literates compared to controls and more late sources in left inferior frontal cortex in control subjects. It is concluded that learning to read in adulthood is a process supported by different brain structures from the ones used when learning occurs at the proper age. This may suggest that the same task can be similarly performed by relying on diverse functional brain anatomic networks.