Surface Dyslexia Research Articles

Improving Phonological Dyslexia Using Electrical Stimulation in the Articulatory System

To the Editor: Dyslexia is a disability characterized by difficulty with reading a text. This disorder includes at least two prominent subtypes; surface dyslexia (individuals cannot correctly utter the irregular words) and phonological dyslexia (individuals cannot correctly utter nonwords); the latter is more common. Phonological dyslexia is diagnosed in individuals who cannot use the alphabetic system (learning the speech sounds that are related to letters), so they cannot correctly utter nonwords. Indeed, patients have problems making connections between sounds and alphabetic symbols. This reading disorder might be related to different neuropsychological or neurobiological pathologies. Many different theories have attempted to explain this kind of dyslexia, one of which is the motor-articulatory feedback theory. According to the motor-articulatory feedback theory, awareness of the positions and movements of the articulatory system (lip, tongue, and jaw) would allow normal individuals to parse a word into its component phonemes. In phonological dyslexia, patients are not aware of these positions and movements and are unable to utter a specific word. If a patient could be made aware of positions and movements of the articulation system, this confliction might probably be improved. Nonspeech oral motor exercises attempt to facilitate range of motion, develop muscle control, and improve the awareness of articulators. These clinical exercises usually include hot, cold, and vibration stimulations to the muscles involved in speech. Although these exercises increase the strength of oral muscles, they have a poor effect on awareness of articulators. In rehabilitation engineering, using electrical stimulation for recovering sensory perception had superior results. For example, using cutaneous electrical stimulation for 3 weeks significantly improved the skin sensation in some muscles of the chronic stroke. According to the results of this effort, and many others focused on awareness recovery by electrical stimulation, bound electrical stimulations seem to have more effect on awareness of articulators in phonological dyslexia cases. Based on the abovementioned points, we hypothesize that bounded electrical stimulations could be more useful than other common nonspeech oral motor exercises for recovering the awareness of the articulatory system in phonological dyslexia. However, experimental research is necessary for validation of this process. Hossein Behbood, M.Sc. Student Mehdii Fallahnezhad, M.Sc. Student Seyyed Ali Seyyedsalehi, Ph.D. Shahriar Gharibzadeh, M.D., Ph.D. Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Islamic Republic of Iran

Eye movement correlates of acquired central dyslexia

Based on recent progress in theory and measurement techniques, the analysis of eye movements has become one of the major methodological tools in experimental reading research. Our work uses this approach to advance the understanding of impaired information processing in acquired central dyslexia of stroke patients with aphasia. Up to now there has been no research attempting to analyze both word-based viewing time measures and local fixation patterns in dyslexic readers. The goal of the study was to find out whether specific eye movement parameters reflect pathologically preferred segmental reading in contrast to lexical reading.We compared oral reading of single words of normal controls (n=11) with six aphasic participants (two cases of deep, surface and residual dyslexia each). Participants were asked to read aloud lines of target words differing in length and frequency. Segmental reading was characterized by deviant spatial distribution of saccadic landing positions with initial fixations located mainly at the beginning of the word, while lexical readers showed the normative ‘preferred landing positions’ left to the center of the words. Contrary to expectation, word length did not distinguish between segmental and lexical readers, while word frequency showed the expected effect for lexical readers only. Their mean fixation duration was already prolonged during first pass reading reflecting their attempts of immediate access to lexical information. After first pass reading, re-reading time was significantly increased in all participants with acquired central dyslexia due to their exceedingly higher monitoring demands for oral reading.

Single or dual orthographic representations for reading and spelling? A study of Italian dyslexic–dysgraphic and normal children

Italian children with surface dyslexia and dysgraphia show defective orthographic lexical processing in both reading and spelling. It is unclear whether this parallelism is due to impairment of separate orthographic input and output lexicons or to a unique defective lexicon. The main aim of the present study was to compare the single- versus dual-lexicon accounts in dyslexic/dysgraphic children (and in normal but younger children). In the first experiment, 9 Italian children with surface dyslexia and dysgraphia judged the orthographic correctness (input lexicon) of their phonologically plausible misspellings (output lexicon) and of phonologically plausible spellings experimentally introduced for words they consistently spelt correctly. The children were generally impaired in recognizing phonologically plausible misspellings. Parallel deficits in reading and spelling also emerged: Children were more impaired in judging items they consistently misspelt and more accurate in judging items they always spelt correctly. In a second experiment, younger normal children with reading/spelling ability similar to that of the dyslexic/dysgraphic children in the first experiment (but younger) were examined. The results confirmed a close parallelism between the orthographic lexical representations used for reading and spelling. Overall, findings support the hypothesis that a single orthographic lexicon is responsible for reading and spelling performance in both dyslexic/dysgraphic and normal (but younger) children.

Computational modelling of the effects of semantic dementia on visual word recognition

Rogers, Lambon Ralph, Hodges, and Patterson (2004) studied two-alternative forced-choice visual lexical decision performance in patients with semantic dementia. With item pairs where the target word was more “typical” (i.e., higher in bigram and trigram frequency) than the foil (all foils were pseudohomophones), lexical decision performance was good and was unaffected by word frequency. With item pairs where the target word was less “typical” (i.e., lower in bigram and trigram frequency) than the foil, lexical decision performance was worse and was affected by word frequency, being particularly inaccurate when the word targets were low in frequency. We show (using as materials all the monosyllabic items used by Rogers and colleagues) that the same pattern of results occurs in the lexical decision performance of the DRC (dual-route cascaded) computational model of reading when the model is lesioned by probabilistic deletion of low-frequency words from its orthographic lexicon. We consider that the PDP (parallel distributed processing) computational model of reading used by Woollams, Plaut, Lambon Ralph, and Patterson (2007) to simulate reading in semantic dementia is not capable of simulating this lexical decision result. We take this, in conjunction with previous work on computational modelling of reading aloud in surface dyslexia, phonological dyslexia, and semantic dementia using the DRC and PDP reading models, to indicate that the DRC model does a better job than the PDP model in accounting for what is known about the various forms of acquired dyslexia.

SD-squared revisited: Reply to Coltheart, Tree, and Saunders (2010).

The connectionist triangle model of reading aloud proposes that semantic activation of phonology is particularly important for correct pronunciation of low-frequency exception words. Our consideration of this issue (Woollams, Lambon Ralph, Plaut, & Patterson, 2007) reported computational simulations demonstrating that reduction and disruption of this semantic activation resulted in the marked deficit in low-frequency exception word reading that is characteristic of surface dyslexia. We then presented 100 observations of reading aloud from 51 patients with semantic dementia (SD) demonstrating a universal decline into surface dyslexia, a phenomenon we termed "SD-squared." Coltheart, Tree, and Saunders have more recently provided a simulation of the SD-squared data within the dual route cascaded (DRC) model, achieved by varying the amount of damage to components of the lexical and nonlexical pathways. Although they suggested that these simulations provide a closer fit to the SD patients' reading data than our own, we demonstrate here that this is not the case. Moreover, we argue that the connectionist triangle model account has substantially greater explanatory and predictive power than the DRC account.

Two forms of surface dyslexia: Simultaneous observations of phonemic errors and pitch-accent errors in Kanji-reading of Japanese semantic dementia patients

Two forms of surface dyslexia: Simultaneous observations of phonemic errors and pitch-accent errors in Kanji-reading of Japanese semantic dementia patients

Surface and phonological developmental dyslexia in Greek

The present study examined whether equivalents of surface and phonological subtypes of developmental dyslexia could be found among a sample of 84 poor readers aged 9–12 years in Greece. Word reading latency was used as a measure of lexical skill, and nonword reading accuracy was used as a measure of nonlexical skill. A simple regression of word reading latencies on nonword reading accuracy scores was performed for 42 developing readers. A total of 2 poor readers with accurate nonword reading plus slow word reading relative to controls (equivalents of surface dyslexia) and 2 poor readers with inaccurate nonword reading plus fast accurate word reading relative to controls (equivalents of phonological dyslexia) were identified from amongst the sample of poor readers. Further testing of these 4 cases on measures of irregular-word and nonword spelling revealed additional evidence of a dissociation between lexical and nonlexical impairments. These results support the notion that dual-route models can be used to explore individual differences among dyslexic readers in transparent orthographic systems such as Greek. An attempt is also made to interpret the results in terms of a double deficit theory of dyslexia (Wimmer, Mayringer, & Landerl, 2000; Wolf & Bowers, 1999).

Dyslexia, dysgraphia, procedural learning and the cerebellum

In this review we focus on the developmental disorders of dyslexia (a disorder of reading) and dysgraphia (a disorder of writing), considering their commonalities and differences with a view to reflecting on the theoretical implications. Interest in dysgraphia was stimulated by the distinction between phonological and surface dyslexia (Castles and Coltheart, 1993), which claimed that orthographic problems (spelling) were separable from phonological reading problems. While this distinction has received mixed support (Snowling et al., 1996; Stanovich et al., 1997) it led to a fruitful analysis not only of the underlying causes of orthographic difficulties, but also to the widespread recognition of developmental difficulties in handwriting control (Deuel, 1995; Manis et al., 1996; Sprenger-Charolles et al., 2000). The result of this theoretical and empirical progress is that there are two usages of the term dysgraphia. One takes dysgraphia to refer to errors of writing that are analogous to errors in reading (e.g., surface, phonological or deep dysgraphia corresponding to surface, phonological and deep dyslexia), the other relating to difficulties in handwriting control. Furthermore, despite these attempts at differentiation, there remains some controversy in the literature as to whether motor difficulties in handwriting should be subsumed under the label dyslexia. This review attempts to tease out the different strands of theoretical research underlying these confusions by analysing explanations of dyslexia and dysgraphia at the cognitive level and the brain level, considering both cortical and sub-cortical systems. First we outline theoretical approaches to developmental dyslexia, introducing causal explanations at the cognitive level, followed by an outline of recent developments in research into motor difficulties in handwriting. We then note the prevalence of comorbidities between developmental

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.

Reading disorders in primary progressive aphasia: A behavioral and neuroimaging study

Previous neuropsychological studies on acquired dyslexia revealed a double dissociation in reading impairments. Patients with phonological dyslexia have selective difficulty in reading pseudo-words, while those with surface dyslexia misread exception words. This double dissociation in reading abilities has often been reported in brain-damaged patients, but it has not been consistently shown in patients with neurodegenerative diseases.In this study, we investigated reading impairments and their anatomical correlates in various neurodegenerative diseases. First, we performed a behavioral analysis to characterize the reading of different word types in primary progressive aphasia (PPA). Then, we conducted a voxel-based morphometry neuroimaging study to map the brain areas in which gray matter volume correlated with the accurate reading of exception and pseudo-words.The results showed a differential pattern of exception and pseudo-word reading abilities in different clinical variants of PPA. Patients with semantic dementia, a disorder characterized by selective loss of semantic memory, revealed a pattern of surface dyslexia, while patients with logopenic/phonological progressive aphasia, defined by phonological loop deficits, showed phonological dyslexia. Neuroimaging results showed that exception word reading accuracy correlated with gray matter volume in the left anterior temporal structures, including the temporal pole, the anterior superior and middle temporal and fusiform gyri, while pseudo-word reading accuracy correlated with left temporoparietal regions, including the posterior superior and middle temporal and fusiform gyri, and the inferior parietal lobule.These results suggest that exception and pseudo-word reading not only rely upon different language mechanisms selectively damaged in PPA, but also that these processes are sustained by separate brain structures.

The role of gene DCDC2 in German dyslexics

Dyslexia is a complex reading and writing disorder with a strong genetic component. In a German case-control cohort, we studied the influence of the suspected dyslexia-associated gene DCDC2. For the first time in a German cohort, we describe association of a 2445 basepair deletion, first identified in an American study. Evidence of association for three DCDC2 single nucleotide polymorphisms (rs807724, rs793862, rs807701), previously identified in German or American cohorts, was replicated. A haplotype of these polymorphisms showed evidence for association as well. Thus, our data further corroborate association of DCDC2 with dyslexia. Analysis of functional subgroups suggests association of investigated DCDC2 variants mainly with nondysphonetic, nonsevere, but probably dyseidetic (surface) dyslexia. Based on the presumed function of DCDC2, our findings point to a role of impaired neuronal migration in the etiology of the disease.

Phonological and Surface Subtypes among University Students with Dyslexia

The prevalence of phonological and surface dyslexia subtypes among Swedish university students with dyslexia (n = 40) was examined using both the regression method, developed by Castles and Coltheart, and latent profile analysis. When an academic‐level control group was used as a reference group in a regression, eight students with phonological dyslexia and 15 students with surface dyslexia were identified. In contrast, 17 students with phonological dyslexia and two students with surface dyslexia were identified when the subtypes were defined by reference to a reading‐level control group, indicating a deviant profile among the students with phonological dyslexia and delayed development among those with surface dyslexia. The latent profile analysis was based on five phonological and four orthographic tasks. Seven profiles were obtained, of which none exhibited deficits in orthographic but not in phonological skills or vice versa. Thus, the analysis further supported the phonological deficit hypothesis of dyslexia.

The association between semantic dementia and surface dyslexia in Japanese

One theory about reading suggests that producing the correct pronunciations of written words, particularly less familiar words with an atypical spelling–sound relationship, relies in part on knowledge of the word's meaning. This hypothesis has been supported by reports of surface dyslexia in large case-series studies of English-speaking/reading patients with semantic dementia (SD), but would have increased credibility if it applied to other languages and writing systems as well. The hypothesis predicts that, of the two systems used to write Japanese, SD patients should be unimpaired at oral reading of kana because of its invariant relationship between orthography and phonology. By contrast, oral reading of kanji should be impaired in a graded fashion depending on the consistency characteristics of the kanji target words, with worst performance on words whose component characters take ‘minority’ (atypical) pronunciations, especially if the words are of lower frequency. Errors in kanji reading should primarily reflect assignment of more typical readings to the component characters in these atypical words. In the largest-ever-reported case series of Japanese patients with semantic dementia, we tested and confirmed this hypothesis.

The association between semantic dementia and surface dyslexia in Japanese

The association between semantic dementia and surface dyslexia in Japanese

Dyslexic Subtypes and Literacy Skills in L2 Opaque English

In theory, opaque orthographies should pose more difficulties for people with developmental dyslexia than transparent ones. (Frost, 2005). However, studies (Miller-Guron & Lundberg, 2000; Van der Leij & Morfidi, 2006) show that some people with dyslexia are better at reading L2 English than their L1 transparent orthography. The current study suggests that they have a form of dyslexia known as phonological dyslexia. On the basis of the dual-route model (Coltheart, 2005), it is proposed that membership of a dyslexic subtype - phonological or surface - influences success in dealing with orthographic depth. To test this, Dutch teenagers with phonological and surface dyslexia performed Dutch and English orthographic competence and spelling tasks. The results seem to indicate that people with phonological dyslexia are more successful in reading English as an L2 opaque than Dutch as an L1 transparent orthography; however, in the case of spelling, the reverse pattern is observed.

The neural basis of surface dyslexia in semantic dementia

Semantic dementia (SD) is a neurodegenerative disease characterized by atrophy of anterior temporal regions and progressive loss of semantic memory. SD patients often present with surface dyslexia, a relatively selective impairment in reading low-frequency words with exceptional or atypical spelling-to-sound correspondences. Exception words are typically 'over-regularized' in SD and pronounced as they are spelled (e.g. 'sew' is pronounced as 'sue'). This suggests that in the absence of sufficient item-specific knowledge, exception words are read by relying mainly on subword processes for regular mapping of orthography to phonology. In this study, we investigated the functional anatomy of surface dyslexia in SD using functional magnetic resonance imaging (fMRI) and studied its relationship to structural damage with voxel-based morphometry (VBM). Five SD patients and nine healthy age-matched controls were scanned while they read regular words, exception words and pseudowords in an event-related design. Vocal responses were recorded and revealed that all patients were impaired in reading low-frequency exception words, and made frequent over-regularization errors. Consistent with prior studies, fMRI data revealed that both groups activated a similar basic network of bilateral occipital, motor and premotor regions for reading single words. VBM showed that these regions were not significantly atrophied in SD. In control subjects, a region in the left intraparietal sulcus was activated for reading pseudowords and low-frequency regular words but not exception words, suggesting a role for this area in subword mapping from orthographic to phonological representations. In SD patients only, this inferior parietal region, which was not atrophied, was also activated by reading low-frequency exception words, especially on trials where over-regularization errors occurred. These results suggest that the left intraparietal sulcus is involved in subword reading processes that are differentially recruited in SD when word-specific information is lost. This loss is likely related to degeneration of the anterior temporal lobe, which was severely atrophied in SD. Consistent with this, left mid-fusiform and superior temporal regions that showed reading-related activations in controls were not activated in SD. Taken together, these results suggest that the left inferior parietal region subserves subword orthographic-to-phonological processes that are recruited for exception word reading when retrieval of exceptional, item-specific word forms is impaired by degeneration of the anterior temporal lobe.

Lexical and nonlexical processing in developmental dyslexia: A case for different resources and different impairments

In a group of adult dyslexics word reading and, especially, word spelling are predicted more by what we have called lexical learning (tapped by a paired-associate task with pictures and written nonwords) than by phonological skills. Nonword reading and spelling, instead, are not associated with this task but they are predicted by phonological tasks. Consistently, surface and phonological dyslexics show opposite profiles on lexical learning and phonological tasks. The phonological dyslexics are more impaired on the phonological tasks, while the surface dyslexics are equally or more impaired on the lexical learning tasks. Finally, orthographic lexical learning explains more variation in spelling than in reading, and subtyping based on spelling returns more interpretable results than that based on reading. These results suggest that the quality of lexical representations is crucial to adult literacy skills. This is best measured by spelling and best predicted by a task of lexical learning. We hypothesize that lexical learning taps a uniquely human capacity to form new representations by recombining the units of a restricted set.

A dual-route perspective on poor reading in a regular orthography: Evidence from phonological and orthographic lexical decisions

Impairments of the lexical and the nonlexical reading route were examined for German-speaking dyslexic readers by measuring accuracy and speed of phonological and orthographic lexical decisions. Different from English-based findings, we found little difficulty with the phonological distinction between pseudohomophones and nonwords, but a major difficulty with the orthographic distinction between words and pseudohomophones. Subtyping identified pure surface dyslexia cases but no case of pure phonological dyslexia. Dyslexic speed impairments were traced to three loci in the dual-route model: an impoverished orthographic lexicon, and slow access from orthographic to phonological lexicon entries (lexical route) and from graphemes to phonemes (nonlexical route). A review of distal cognitive deficits suggested that the orthographic lexicon is affected by phonological deficits and that the slow functioning of the lexical and the nonlexical route reflects a general visual-verbal speed impairment and not a purely visual-attentional deficit.

The left fusiform area is affected by written frequency of words

The recent neuroimaging literature gives conflicting evidence about whether the left fusiform gyrus (FG) might recognize words as unitary visual objects. The sensitivity of the left FG to word frequency might provide a neural basis for the orthographic input lexicon theorized by reading models [Patterson, K., Marshall, J. C., & Coltheart, M. (1985). Surface dyslexia: Cognitive and neuropsychological studies of phonological reading. London: Lawrence Erlbaum]. The goal of this study was to investigate the time course and neural correlates of word processing in right-handed readers engaged in an orthographic decision task. Three hundred and twenty Italian words of high and low written frequency and 320 non-derived legal pseudo-words were presented for 250ms in the central visual field. ERPs were recorded from 128 scalp sites in 10 Italian University students. Behavioural data showed a word superiority effect, with faster RTs to words than pseudo-words. Left occipito/temporal N2 (240ms) was greater to high-frequency than low-frequency words and pseudo-words. According to the swLORETA inverse solution, the underlying neural source of this effect was located in the left fusiform gyrus of the occipital lobe (X=−29, Y=−66, Z=−10, BA19) and the right superior temporal gyrus (X=51, Y=6, Z=−5, BA22), which are probably involved in word recognition and semantic representation, respectively. Later frontal ERP components, LPN (300–350) and P3 (400–500), also showed strong lexical sensitivity, thus suggesting implicit semantic processes. The results shed some light on the possible neural substrate of visual reading disabilities such as developmental surface dyslexia or pure alexia.

Developmental surface dyslexias

Individuals with surface dyslexia read via grapheme-to-phoneme conversion due to a deficit in the lexical route. A deficit in the lexical route can be caused by impairments at several different loci. In the current study we identify three subtypes of developmental surface dyslexia, each caused by impairment at a different locus on the lexical route, and each showing a different pattern of performance in various tasks. All three subtypes show the classical pattern of reading aloud, with regularizations and difficulty in reading words that have more than a single possible conversion to a phoneme string, but they differ in their performance in lexical decision and homophone comprehension. The first subtype, input surface dyslexia, results from a deficit to the orthographic input lexicon, and entails poor performance in lexical decision and comprehension tasks. The second subtype, orthographic lexicon output surface dyslexia, in which the orthographic input lexicon is accessible but its output to the phonological output lexicon and to the semantic system is impaired, allows normal lexical decision, but causes impaired comprehension of homophones. The third subtype, interlexical surface dyslexia, caused by a selective deficit in the connection between the orthographic input lexicon and the phonological output lexicon but with intact access from the orthographic input lexicon to the semantic system, allows normal performance in lexical decision and comprehension tasks. Seventeen Hebrew-speaking individuals with developmental surface dyslexia aged 10–43 participated in the study, eight of them showed the first pattern, three showed the second pattern, and six displayed the third pattern. Another result of the study pertains to the importance of the lexicality of the result of grapheme-to-phoneme conversion for each target word. Some words, when read via grapheme-to-phoneme conversion, can potentially be read as other words (such as “now” in English, which can be sounded as the word “know”), we term these words potentiophones. The results indicate that potentiophones yield the highest error rate in reading aloud for all the participants with surface dyslexia.