Subtypes Of Dyslexia Research Articles

Verbal Fluency in Children: Developmental Issues and Differential Validity in Distinguishing Children with Attention-Deficit Hyperactivity Disorder and Two Subtypes of Dyslexia

Previous research studies have shown that in adults, verbal fluency is impaired after lesion to the frontal lobes and left temporal lobe. More recently, there have been a few studies reported which indicated that in children, like adults, left hemisphere and frontal lesions result in pronounced effects on verbal fluency. The present study examined developmental differences in verbal fluency within a sample of 130 normal children, aged 6 to 12 years. Additionally, the same verbal fluency test was administered to two subgroups of children with developmental dyslexia and a group of children with attention-deficit/hyperactivity disorder (ADHD). Analysis of variance (ANOVA) revealed significant between-group differences by age in the normal children. Further, ANOVA demonstrated that the verbal fluency measure was clinically useful in differentiating the Language Disorder/Dysphonetic Dyslexic subgroup from the Visual-Spatial/Dyseidetic Dyslexic subgroup and the ADHD group, with the latter two groups performing within the average range

Verbal Fluency in Children: Developmental Issues and Differential Validity in Distinguishing Children with Attention-Deficit Hyperactivity Disorder and Two Subtypes of Dyslexia

Previous research studies have shown that in adults, verbal fluency is impaired after lesion to the frontal lobes and left temporal lobe. More recently, there have been a few studies reported which indicated that in children, like adults, left hemisphere and frontal lesions result in pronounced effects on verbal fluency. The present study examined developmental differences in verbal fluency within a sample of 130 normal children, aged 6 to 12 years. Additionally, the same verbal fluency test was administered to two subgroups of children with developmental dyslexia and a group of children with attention-deficit/hyperactivity disorder (ADHD). Analysis of variance (ANOVA) revealed significant between-group differences by age in the normal children. Further, ANOVA demonstrated that the verbal fluency measure was clinically useful in differentiating the Language Disorder/Dysphonetic Dyslexic subgroup from the Visual-Spatial/Dyseidetic Dyslexic subgroup and the ADHD group, with the latter two groups performing within the average range.

The Balance Model of Dyslexia and Remedial Training

The aim of this study was to test the validity of Bakker's (1983, 1990) theory and treatment paradigm of dyslexia. Twenty-one children (mean age = 9.9 years) categorized as P-type dyslexics (showing accurate but slow and fragmented reading) and 19 children (mean age = 9.7 years) categorized as L-type dyslexics (fast but inaccurate readers) were presented with hemisphere-specific stimulation (HSS) and hemisphere-alluding stimulation (HAS). HSS was produced by presenting words to either the left or the right visual half-field, or to the left or right hand of the participant. HAS training was achieved through the presentation of either semantically/phonetically demanding or perceptually demanding text. Participants were given either a treatment program that was specifically designed for their particular dyslexia subtype, or a program that had been deliberately chosen to be inconsistent with their subtype. Contrary to predictions, participants made gains on all of the reading measures, regardless of the type of treatment given. On the basis of these findings it is suggested that treatment gains made are due to nonspecific training effects and not to the specific nature of Bakker's remedial strategies.

Normal planum temporale asymmetry in dyslexics with a magnocellular pathway deficit.

Developmental dyslexia has been associated with both abnormal hemispheric symmetry of the planum temporale (PT) and a deficit in the magnocellular visual pathway. We examined the relationship between these two abnormalities. Using sagittal magnetic resonance images and three methods, we measured the PT in dyslexic subjects with a documented magnocellular deficit and controls. Dyslexic subjects did not deviate from normal leftward PT asymmetry, but both groups became less left-lateralized with methods that excluded sulcul tissue. Results suggest that dyslexic subjects with a magnocellular deficit do not always have abnormal symmetry of the PT. PT symmetry may instead be related to a different subtype of dyslexia. In addition, PT asymmetry in any subject group depends on the measurement method.

Varieties of Developmental Reading Disorder: Genetic and Environmental Influences

There is widespread support for the notion that subgroups of dyslexics can be identified who differ in their reading profiles: Developmental phonological dyslexia is characterized by poor nonword reading, while developmental surface dyslexia is distinguished by a particular difficulty in reading irregular words. However, there is much less agreement about how these subtypes, and particularly the surface dyslexic pattern, are to be accounted for within theoretical models of the reading system. To assist in addressing this issue, the heritability of reading deficits in dyslexic subtypes was examined using a twin sample. Subjects’ scores on (a) an exception word reading task and (b) a nonword reading task were used to create a subtype dimension, and surface and phonological dyslexic subgroups were selected from the ends of this distribution. Reading deficits were found to be significantly heritable in both subgroups. However, the genetic contribution to the group reading deficit was much greater in the phonological dyslexics than in the surface dyslexics. The finding of differential genetic etiology across subtypes suggests that there is at least partial independence in the development of the cognitive processes involved in reading exception words and nonwords. Also, the results support accounts of surface dyslexia which emphasize a strong environmental contribution.

Reading ability and processing in Duchenne muscular dystrophy and spinal muscular atrophy.

We analysed the reading abilities and processing of 21 children with Duchenne muscular dystrophy (DMD), 11 matched children suffering from spinal muscular atrophy (SMA) and 42 children receiving normal education. The principal result observed was that the DMD children exhibited a reading age which was significantly lower than the SMA children compared with their chronological age. These learning disabilities were not related to a deficit in non-verbal performance intelligence, but psycholinguistic evaluation showed a deficit in verbal intelligence, especially in the Similarities and Arithmetic WISC-R subtests, in phonological abilities, oral word repetition, and in digit span score. The results for the DMD children were heterogeneous, and ranged from normal to greater or lesser involvement. In an attempt to clarify the nature of this reading impairment in DMD children, the three groups (DMD, SMA, and normal control children) were tested by reading aloud a list of single words and non-words. The DMD children were significantly impaired in reading non-words, suggesting reading disability similar to dysphonetic dyslexia, the most frequent subtype of developmental dyslexia. These results are discussed in the light of psychometric data available for our DMD population and in the light of previous studies. The practical consequences of diagnosis on rehabilitation are very important. The precise description of the cognitive deficits seen in DMD is of value for future clinical and genetic studies.

Converging evidence for phonological and surface subtypes of reading disability.

Using regression-based procedures introduced by A. Castles and M. Coltheart (1993), the authors identified 17 phonological and 15 surface dyslexics from a sample of 68 reading-disabled 3rd-grade children by comparing them to chronological-age (CA) controls on exception word and pseudoword reading. However, when the dyslexic subtypes were defined by reference to reading-level (RL) controls, 17 phonological dyslexics were defined but only 1 surface dyslexic. When the CA-defined subtypes were compared to RL controls, the phonological dyslexics displayed superior exception word reading but displayed deficits in pseudoword naming, phonological sensitivity, working memory, and syntactic processing. The surface dyslexics, in contrast, displayed a cognitive profile remarkably similar to that of the RL controls.

Subtypes of developmental dyslexia and lexical acquisition

Although much has been learned about the nature and etiology of impairments in sublexical translation skills, less is known about the difficulties of children who are poor at recognising words as whole orthographic units. In the research described here, an attempt was made to look closely at the process these poor readers go through when trying to acquire new lexical information. Groups of poor readers were required to learn the pronunciations of a set of “irregular” nonsense words over a series of training sessions. There was an imperfect correspondence between the orthographic and phonological forms of these items, so grapheme-phoneme conversion rules could not be used (e. g., macht was pronounced “mot”). The results indicated that this learning task distinguishes between poor readers with a specific lexical deficit and those with a different type of reading difficulty. Ways in which this kind of task might usefully be employed in future research in this area are discussed.

Family patterns of developmental dyslexia, part II: behavioral phenotypes.

The motor control of bimanual coordination and motor speech was compared between first degree relatives from families with at least 2 dyslexic family members, and families where probands were the only affected family members. Half of affected relatives had motor coordination deficits; and they came from families in which probands also showed impaired motor coordination. By contrast, affected relatives without motor deficits came from dyslexia families where probands did not have motor deficits. Motor coordination deficits were more common and more severe among affected offspring in families where both parents were affected than among affected offspring in families where only one parent was affected. However, motor coordination deficits were also more common and more severe in affected parents when both parents were affected than among affected parents in families where only one parent was affected. We conclude that impaired temporal resolution in motor action identifies a behavioral phenotype in some subtypes of developmental dyslexia. The observed pattern of transmission for motor deficits and reading impairment in about half of dyslexia families was most congruent with a genetic model of dyslexia in which 2 codominant major genes cosegregate in dyslexia pedigrees where the proband is also motorically impaired.

Dichotic listening performance under high and low lexical work load in subtypes of developmental dyslexia

This study examined dichotic listening performance in different subtypes of developmental dyslexia under high and low verbal work load conditions. Free recall tests of digits and words were administered to 320 dyslexic children from grade 3 to grade 10 and their matched controls. Results indicate significant differences within subtypes. Surface dyslexics manifested extreme ear neglect or total performance collapse but only under high verbal work load conditions. Phonological dyslexia was distinguished by poor total performance both under high and low work load levels. Visuo-motor dyslexics, however, did not differ in any measure from their controls. These results lend support to the contention that the main neuropsychological factor impeding reading acquisition varies according to dyslexia subtype.

Is there a visual dyslexia

Traditionally, it has been speculated that weaknesses in the visual processing of cognitive aspects of the written word could lead to reading problems, and if so, such a condition would constitute a subtype of developmental dyslexia. This putative subtype has been referred to as visual dyslexia. In this article, the role of cognitive deficits that are visual in nature as a potential etiological factor of developmental dyslexia is examined. Following a brief history of the study of dyslexia, a critique of studies of visual dyslexia is presented. Subsequently, the nature of the visual processes involved in word- recognition is examined. Finally, three research studies that assessed the contribution of visual memory to word-recognition are presented. It is concluded that, even though defects in the physiological aspects of visual processing can lead to reading difficulties, at present little convincing evidence is available to conclude that a subtype of dyslexia caused by cognitive deficits associated with visual processing of information exists.

Dyslexic subtypes and severity levels: are there gender differences?

The prevalence of dyslexia among 100 children participating in a longitudinal study was examined. At age 10 years, The Dyslexia Screener (TDS) test, a direct assessment of coding skills used in reading and spelling, was administered. The incidence of suspected dyslexia of borderline or worse severity among boys and girls was not significantly different, nor did males and females differ significantly in terms of TDS-suspected dyslexic types of severity levels. Results challenge the widely held belief of an increased incidence of reading disability among males and, in conjunction with findings from other recent studies, underscore the need for establishing objective and reliable screening procedures in addition to teacher referral in identifying children in need of special services. Possible factors mediating previous estimates of incidence and the implications of these findings are discussed.

Validation of a Clinical Method for the Diagnosis of Two Subtypes of Dyslexia

Children with dyslexia were identified and subtyped by two testing methods, word attack and analysis of spelling errors. A phonologically impaired group (n = 54) and an orthographically impaired group (n = 20) were selected from a mid-elementary-school-level referred population for an intervention program. The subtype diagnostic methods were validated by a double dissociation between the groups on a variety of independent measures of phonological and orthographic processing. Phonologically impaired children with dyslexia showed poorer higher-order phonics processing skills, such as sound integration, than did orthographically impaired children with dyslexia. The groups did not differ on lower-order phonics processing skills, such as rhyming or segmentation. Orthographically impaired children showed poorer recognition of nonwords and slower reading speed than did phonologically impaired children. These subtype diagnostic methods can provide clinically important information about dyslexic children's mental processing strengths and weaknesses.

Dichotic listening performance in subtypes of developmental dyslexia and a left temporal lobe brain tumor contrast group

This study examined dichotic listening performance in three subtypes of developmental dyslexia and in children with left temporal lobe brain tumors (clinical contrast group). Each child was administered a free-recall CV syllable dichotic paradigm (30 pairs). Analysis of variance and Tukey-HSD pairwise follow-up comparison indicated that the dichotic listening performance of the left temporal lobe brain tumor contrast group (strong LEA/right ear suppression) was significantly different from those of the visual-spatial/dyseidetic (strong REA/left ear depression) and mixed (moderate REA/bilateral ear suppression) dyslexic subtypes. The language disorder/dysphonetic dyslexic subtype demonstrated a REA with right ear depression. Closer inspection of the individual performances of the language disorder/dysphonetic dyslexic subtype revealed a bimodal distribution with 12 subjects demonstrating a strong LEA/right ear suppression and 8 subjects exhibiting a strong REA/left ear depression. These results lend support for the contention that the dyslexic population is heterogeneous in nature with each subgroup exhibiting (1) a distinct neuropsychological test profile and reading pattern and (2) a pattern of performance on the dichotic listening task which is consistent with what would be expected based upon the pattern of dysfunction exhibited on neuropsychological evaluation.

Neurological aspects of dyslexia: comment on the balance model.

The Balance Model rests on a long history of research that suggests that different subtypes of dyslexia exist. Based on the notion that there are two subtypes of dyslexia, Bakker has articulated a developmental neuropsychological model whereby a procedure known as hemisphere-specific stimulation may be beneficial in treatment. This article reviews Bakker's model and provides a critical examination as to why validating research has not been conducted. While Bakker's Balance Model may hold promise for scientific inquiry, validation of treatment effects are needed prior to employing these procedures in clinical practice. Further, important conceptual issues remain to be addressed.

Electrophysiological Correlates of Dyslexic Subtypes

The construct validity of Boder's typology of dyslexia was investigated using quantified EEG. Thirty-nine children, ranging in age from 7-0 to 10-11, were recorded during a contextual reading task and at rest. During reading, children with dyslexia were expected to show increased theta and beta amplitude compared to nondisabled readers. These differences were expected in regions of presumed strength for each subtype as a sign of overengagement in task. Children with phonological deficits (dysphonetic dyslexia) were expected to adopt visuospatial processing strategies (right occipital-parietal activation), those with orthographic deficits (dyseidetic dyslexia) to emphasize phonetic strategies (left temporal-parietal activation). Results supported beta frequency differences in anticipated regions by subtype during the reading task. However, the direction of difference hypothesis was not supported. Decreased amplitudes in both groups with dyslexia compared to normally achieving readers suggest reconceptualization of the theoretical base for the Boder subtyping system.

Dyslexics and normal beginning readers read by different strategies: a comparison of strategy distributions in dyslexic and normal readers1

Research on subtypes of developmental dyslexia often implies that dyslexics fall into discrete groups with different reading strategies and underlying deficits. Recently this assumption has been questioned (Stanovich 1989). However, the distributions of reading strategies in groups of dyslexic and normal readers have never been compared. With this aim, the present study compared the individual reading strategies in a group of 26 severely impaired developmental dyslexics with strategies in a reading‐level‐matched group of 26 younger, normal readers. It was found that reading skills and strategies were distributed over a continuum in both groups. The dyslexic subjects were specifically impaired in phonological processing, however, and half of them read by means of more whole‐word oriented strategies than any of the normal controls. These findings contest current subtype theory and clinical practice (e.g. Boder & Jarrico 1982).

Hemisphere-Specific Treatment of Dyslexia Subtypes: A Field Experiment

Evidence is discussed to show that so-called L- and P-type dyslexia result from deviations in the development of hemispheric subservience in learning to read. Investigations into the validity of the L/P classification are reviewed, as are laboratory experiments on the effects of so-called hemisphere-specific stimulation (HSS). In the present field experiment, 28 L-dyslexic children (mean chronological and reading age 10.6 and 7.5 years, respectively) received HSS of the right hemisphere by the presentation of words to the fingers of the left hand, and 26 P-dyslexic children (mean chronological and reading age 9.4 and 7.2 years, respectively) received HSS of the left hemisphere by the presentation of words to the fingers of the right hand. Control L and P subjects were treated according to the discretion of the remedial teacher. The results underscore the findings of previous laboratory experiments in that (a) HSS-treated L-dyslexics, relative to controls, tended to show larger improvement of accuracy in text reading; and (b) HSS-treated P-dyslexics, relative to controls, showed larger improvement of fluency in word reading.

Boder's Subtypes of Dyslexia

The subtyping of dyslexic children proposed by Boder (1971, 1973) have been validated by quantitative neurophysiological techniques at the Gunderson Medical Foundation, LaCrosse, WI.

Improving the reading comprehension of children with dysphonetic and dyseidetic dyslexia using story grammar.

Five 8- to 10-year-old children with dysphonetic and dyseidetic dyslexia were given instruction in reading comprehension using a story grammar strategy in which story instruction was differentially designed to match the simultaneous or sequential mental processing strengths of each dyslexia subtype. A multiple baseline, single subject experimental design and statistical analyses indicated that the experimental treatments yielded statistically and clinically significant improvements in the proportion of qualitatively important story elements recalled by the subjects, when compared to baseline traditional remedial instruction. The results suggested that students with dyslexia can increase their reading comprehension with training in metacognitive strategies. The question of whether the results were attributable to the subtype-matched methods per se or to strategy training in general, as well as a number of methodological issues, is being explored in subsequent research.