Differentiating the neural response to intervention in children with developmental dyslexia

Developmental dyslexia is associated with functional abnormalities within reading areas of the brain. For some children diagnosed with dyslexia, phonologically based remediation programs appear to rehabilitate brain function in key reading areas (Shaywitz et al., Biological Psychiatry 55: 101–110, 2004; Simos et al., Neuroscience 58: 1203–1213, 2002). However, a non-trivial number of children diagnosed with dyslexia fail to respond to these interventions (Torgesen, Learning Disabilities Research & Practice 15: 55–64, 2000). A cross-sectional fMRI study investigating post-treatment effects was conducted in an effort to better understand differences in brain function between treatment responders and non-responders. Educational testing and brain activation measured after treatment suggested that the reading intervention used in the present study rehabilitated several basic level reading processes in all participants diagnosed with dyslexia. However, activation in the left inferior parietal lobe differentiated treatment responders and non-responders in comparison to non-impaired readers. Children with persistent deficits in single word decoding (treatment non-responders) demonstrated significantly less activation in the left inferior parietal lobe when compared to non-impaired readers.     

Investigating the double-deficit hypothesis of developmental dyslexia in an orthography of intermediate depth

The present study aimed to investigate the double-deficit hypothesis (DDH) in an orthography of intermediate depth. Eighty-five European Portuguese-speaking children with developmental dyslexia, aged 7 to 12, were tested on measures of phonological awareness (PA), naming speed (NS), reading, and spelling. The results indicated that PA and NS were not significantly correlated, and that NS predicts reading fluency (but not reading accuracy and spelling) beyond what is accounted for by PA. Although the majority of the children with developmental dyslexia have double deficit (62.4%), some children have a single phonological deficit (24.7%) or a single NS deficit (8.2%). Children with a double deficit were not more impaired in reading fluency, reading accuracy, and spelling than both single-deficit subtypes. In conclusion, the findings of the present study are partially consistent with the DDH and provide evidence for the multifactorial model of developmental dyslexia. Implications of the DDH for an orthography of intermediate depth are emphasized.

     

Reading development and dyslexia in a transparent orthography: a survey of Spanish children

Spanish-speaking children learn to read words printed in a relatively transparent orthography. Variation in orthographic transparency may shape the architecture of the reading system and also the manifestation of reading difficulties. We tested normally developing children and children diagnosed with reading difficulties. Reading accuracy was high across experimental conditions. However, dyslexic children read more slowly than chronological age (CA)-matched controls, although, importantly, their reading times did not differ from those for ability-matched controls. Reading times were significantly affected by frequency, orthographic neighbourhood size and word length. We also found a number of significant interaction effects. The effect of length was significantly modulated by reading ability, frequency and neighbourhood. Our findings suggest that the reading development of dyslexic children in Spanish is delayed rather than deviant. From an early age, the salient characteristic of reading development is reading speed, and the latter is influenced by specific knowledge about words.     

Semantic effects on word naming in children with developmental dyslexia

Repetition priming was used to examine whether children with dyslexia bias a lexical–semantic pathway when reading words aloud. For the dyslexic group (n = 18, age 9.4–11.8 years), but not for age‐matched controls (n = 18, age 9.2–12.4 years), reaction times when naming pictures were faster after naming the corresponding word. A reading age‐matched control group (n = 24, age 6.8–8.9 years) showed similar priming effects to the children with dyslexia. The magnitude of repetition priming was greater for children with dyslexia with poor nonword reading and slower picture naming. Assuming repetition priming of picture naming is contingent on accessing lexical phonology via semantics, the results suggest less‐skilled normal and disordered readers show a stronger bias towards a lexical– semantic pathway during word reading than skilled readers, and the severity of the phonological representations deficit modulates the strength of that bias in children with dyslexia.     

Developmental dyslexia in an orthography of intermediate depth: the case of European Portuguese

Fifteen Portuguese children with dyslexia, aged 9–11 years, were compared with reading and chronological age controls with respect to five indicators related to the phonological deficit hypothesis: the effects of lexicality, regularity, and length, implicit and explicit phonological awareness, and rapid naming. The comparison between groups indicates that Portuguese children with dyslexia have a phonological impairment which is revealed by a developmental deficit in implicit phonological awareness and irregular word reading (where younger reading level controls performed better than dyslexics) and by a developmental delay in decoding ability and explicit phonological awareness (where dyslexics matched reading level controls). These results are discussed in relation to the idea that European Portuguese is written in an orthography of intermediate depth.     

Effects of bottom-up and top-down intervention principles in emergent literacy in children at risk of developmental dyslexia: a longitudinal study

This longitudinal study focused on the effects of two different principles of intervention in children at risk of developing dyslexia from 5 to 8 years old. The children were selected on the basis of a background questionnaire given to parents and preschool teachers, with cognitive and functional magnetic resonance imaging results substantiating group differences in neuropsychological processes associated with phonology, orthography, and phoneme-grapheme correspondence (i.e., alphabetic principle). The two principles of intervention were bottom-up (BU), "from sound to meaning", and top-down (TD), "from meaning to sound." Thus, four subgroups were established: risk/BU, risk/TD, control/BU, and control/TD. Computer-based training took place for 2 months every spring, and cognitive assessments were performed each fall of the project period. Measures of preliteracy skills for reading and spelling were phonological awareness, working memory, verbal learning, and letter knowledge. Literacy skills were assessed by word reading and spelling. At project end the control group scored significantly above age norm, whereas the risk group scored within the norm. In the at-risk group, training based on the BU principle had the strongest effects on phonological awareness and working memory scores, whereas training based on the TD principle had the strongest effects on verbal learning, letter knowledge, and literacy scores. It was concluded that appropriate, specific, data-based intervention starting in preschool can mitigate literacy impairment and that interventions should contain BU training for preliteracy skills and TD training for literacy training.     

Artificial grammar learning in primary school children with and without developmental dyslexia

This paper explores implicit learning in typically developing and primary school children (9–12 years old) with developmental dyslexia using an artificial grammar learning (AGL) task. Two experiments were conducted, which differed in time of presentation and nature of the instructional set (experiment 1—implicit instructions vs experiment 2—explicit instructions). Repeated measures analysis of variance (group × grammaticality × chunk strength) showed a group effect only in experiment 1 (implicit instructions), with only the typically developing children showing evidence of AGL. There was a grammaticality effect (adherence to the rules) for both groups in the two experimental situations. We suggest that the typically developing children exhibited intact implicit learning as manifested in AGL performance, whereas children with developmental dyslexia failed to provide such evidence due to possible mediating cognitive developmental factors.     

Atypical predictive processing during visual statistical learning in children with developmental dyslexia: an event-related potential study

Previous research suggests that individuals with developmental dyslexia perform below typical readers on non-linguistic cognitive tasks involving the learning and encoding of statistical-sequential patterns. However, the neural mechanisms underlying such a deficit have not been well examined. The aim of the present study was to investigate the event-related potential (ERP) correlates of sequence processing in a sample of children diagnosed with dyslexia using a non-linguistic visual statistical learning paradigm. Whereas the response time data suggested that both typical and atypical readers learned the statistical patterns embedded in the task, the ERP data suggested otherwise. Specifically, ERPs of the typically developing children (n?=?12) showed a P300-like response indicative of learning, whereas the children diagnosed with a reading disorder (n?=?8) showed no such ERP effects. These results may be due to intact implicit motor learning in the children with dyslexia but delayed attention-dependent predictive processing. These findings are consistent with other evidence suggesting that differences in statistical learning ability might underlie some of the reading deficits observed in developmental dyslexia.     

Dutch home-based pre-reading intervention with children at familial risk of dyslexia

Children (5 and 6 years old, n = 30) at familial risk of dyslexia received a home-based intervention that focused on phoneme awareness and letter knowledge in the year prior to formal reading instruction. The children were compared to a no-training at-risk control group (n = 27), which was selected a year earlier. After training, we found a small effect on a composite score of phoneme awareness (d = 0.29) and a large effect on receptive letter knowledge (d = 0.88). In first grade, however, this did not result in beneficial effects for the experimental group in word reading and spelling. Results are compared to three former intervention studies in The Netherlands and comparable studies from Denmark and Australia.     

Amplitude envelope perception, phonology and prosodic sensitivity in children with developmental dyslexia

Here we explore relations between auditory perception of amplitude envelope structure, prosodic sensitivity, and phonological awareness in a sample of 56 typically-developing children and children with developmental dyslexia. We examine whether rise time sensitivity is linked to prosodic sensitivity, and whether prosodic sensitivity is linked to phonological awareness. Prosodic sensitivity was measured by two reiterant speech tasks modelled on Kitzen (2001). The children with developmental dyslexia were significantly impaired in the reiterant speech tasks and in the phonological awareness tasks (onset and rime awareness). There were significant predictive relations between basic auditory processing of amplitude envelope structure (in particular, rise time), prosodic sensitivity, phonological awareness, reading, and spelling. The auditory processing difficulties that characterise children with developmental dyslexia appear to impair their sensitivity to phrase-level prosodic cues such as metrical structure as well as to phonology, but in this study phonological and prosodic sensitivity made largely independent contributions to reading.     

Word length and word frequency affect eye movements in dyslexic children reading in a regular (German) orthography

We combined independently the word length and word frequency to examine if the difficulty of reading material affects eye movements in readers of German, which has high orthographic regularity, comparing the outcome with previous findings available in other languages. Sixteen carefully selected German-speaking dyslexic children (mean age, 9.5 years) and 16 age-matched controls read aloud four lists, each comprising ten unrelated words. The lists varied orthogonally in word length and word frequency: high-frequency, short; high-frequency, long; low-frequency, short; low-frequency, long. Eye movements were measured using a scanning laser ophthalmoscope (SLO). In dyslexic children, fixation durations and the number of saccades increased both with word length and word frequency. The percentage of regressions was only increased for low-frequency words. Most of these effects were qualitatively similar in the two groups, but stronger in dyslexic children, pointing to a deficient higher-level word processing, especially phonological deficit. The results indicate that reading eye movements in German children are modulated by the degree of difficulty, and orthographic regularity of the language can determine the nature of modulation. The findings suggest that, similar to Italian but unlike English readers, German children prefer indirect sub-lexical strategy of grapheme-phoneme conversion.     

Sentence comprehension in young adults with developmental dyslexia

This study investigated the effects of syntactic complexity on written sentence comprehension in compensated adults with dyslexia. Because working memory (WM) plays a key role in processing complex sentences, and individuals with dyslexia often demonstrate persistent deficits in WM, we hypothesized that individuals with dyslexia would perform more poorly on tasks designed to assess the comprehension of syntactic structures that are especially taxing on WM (e.g., passives, sentences with relative clauses). Compared to their nondyslexic peers, individuals with dyslexia were significantly less accurate and marginally slower on passive sentences. For sentences containing relative clauses, the dyslexic group was also less accurate but did not differ in response times. Covarying WM and word reading in both analyses eliminated group differences showing that syntactic deficits in adults with dyslexia are constrained by both WM and word-reading ability. These findings support previous research showing that syntactic processing deficits are characteristic of dyslexia, even among high-achieving students.     

The early manifestation of developmental dyslexia: Evidence from German children

The present study retrospectively examined early difficulties with phonological coding and phonemic segmentation of German children who after four years in school were diagnosed as dyslexic. German, in comparison to English, exhibits rather simple and straight-forward grapheme-phoneme correspondences, and the initial teaching approach was phonics oriented. Despite these favorable circumstances for the acquisition of phonological coding, the majority of the later dyslexic children had particular difficulties with the accurate reading of nonwords and of unfamiliar words after about seven months of reading instruction. However, there were enormous differences between the dyslexic children. Two of them were completely unable to blend phonemes into pronunciations, another seven were slow and error prone decoders, and three children had slow and laborious pronunciation assembly as the core problem. The majority of the later dyslexic children also exhibited phonemic segmentation deficits as tested with a nonword spelling task and a phoneme reversal task. In correspondence with findings from older German dyslexic children, the early difficulties with accurate phonological coding and phonemic segmentation were no longer found at the end of grade four. Children then suffered from very slow reading and poor spelling. In general, the difficulties of German dyslexic children emphasize the phonological impairment account of dyslexia. More specifically, these findings suggest that the assembly of letter sounds into pronunciations is particularly affected in the early phase of learning to read a consistent orthography.     

Orthographic processing is a key predictor of reading fluency in good and poor readers in a transparent orthography

We used structural equation modeling to investigate sources of individual differences in oral reading fluency in a transparent orthography, Russian. Phonological processing, orthographic processing, and rapid automatized naming were used as independent variables, each derived from a combination of two scores: phonological awareness and pseudoword repetition, spelling and orthographic choice, and rapid serial naming of letters and digits, respectively. The contribution of these to oral text-reading fluency was evaluated as a direct relationship and via two mediators, decoding accuracy and unitized reading, measured with a single-word oral reading test. The participants were “good” and “poor” readers, i.e., those with reading skills above the 90th and below the 10th percentiles (n = 1344, grades 2–6, St. Petersburg, Russia). In both groups, orthographic processing skills significantly contributed to fluency and unitized reading, but not to decoding accuracy. Phonological processing skills did not contribute directly to reading fluency in either group, while contributing to decoding accuracy and, to a lesser extent, to unitized reading. With respect to the roles of decoding accuracy and unitized reading, the results for good and poor readers diverged: in good readers, unitized reading, but not decoding accuracy, was significantly related to reading fluency. For poor readers, decoding accuracy (measured as pseudoword decoding) was related to reading fluency, but unitized reading was not. These results underscore the importance of orthographic skills for reading fluency even in an orthography with consistent phonology-to-orthography correspondences. They also point to a qualitative difference in the reading strategies of good and poor readers.     

Lexical priming of nonword spelling in the regular orthography of Italian

In pronounced contrast to English, Italian orthography contains extremely regular sound-to-spelling correspondences and therefore Italian words could, in principle, be spelled perfectly correctly using nonlexical phoneme-to-grapheme conversion rules alone. If this were so, then there should be no lexical influence upon nonword spelling. However, the present experiment reports lexical priming effects for two inconsistently spelled segments in Italian words: Italian participants were more likely to spell the nonword tece as TECIE if they had just heard the word specie rather than pece and were more likely to spell the nonword cuodo as QUODO if they had heard the word quota rather than cuoco. These results suggest that Italian, despite its regular orthography, is not spelled purely nonlexically. It is argued that a dual-route model of spelling production can be applied to Italian.     

Using computer-based readers to improve reading comprehension of students with dyslexia

Twenty-eight middle school students, diagnosed as dyslexic and attending a school using the Slingerland approach to remediation of dyslexia, used a computer-based reading system for reading literature for about one-half hour a day for a semester. The system proved to be a strong compensatory aid, enabling 70 percent of the students to read with greater comprehension, approximately one grade level or more improvement, as measured by the Gray Oral Reading Test. For 40 percent of the students, the gains were large, from two to as much as five grade levels. However, not all students benefited. Fourteen percent showed lower comprehension scores when using the system, and there is some indication that this degradation is associated with kinesthetic-motor weakness. Some students reported gains in reading speed and exhibited increased span of attention for and endurance in reading when using the system. We did not find evidence that the computer-reader technology provided a positive remediation benefit incremental to that obtained from the school’s intensive Slingerland remediation program. Our results indicate that computer-readers are important compensatory aids that can enable many people with dyslexia to perform more effectively in reading-related tasks associated with school and work.