On subtypes of developmental dyslexia: evidence from processing time and accuracy scores.

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.

Cortical and behavioral correlates of alexia in primary progressive aphasia and Alzheimer's disease.

Two ways of subtyping in dyslexia will be examined, namely visual/auditory (or ‘dyseidetic’/‘dysphonetic’) and phonological/surface. The conventional view is that phonological dyslexics have difficulty with non-words but are relatively stronger at real words, whereas the surface dyslexic can manage non-words but has difficulty with irregular words. When errors were classified into ‘visual’ and ‘auditory’, it was found in the case of 68 dyslexic children that after a 2-year period of tuition there was a change in the ratio of ‘visual’ errors to ‘auditory’ errors—the proportion of ‘auditory’ errors decreasing markedly. Also, when suitable regular words, non-words and irregular words were given to 58 dyslexic children and to 58 younger children matched for reading age, in neither group did the pattern of results give any significant support for classifying dyslexic children into ‘phonological dyslexics’ or ‘surface dyslexics’. A more economical hypothesis, which explains both sets of results, is that the observed changes reflect the instruction which the children had received. The alternative hypothesis, namely that there is some kind of ‘cognitive substrate’ which remains unchanged whatever the kind of teaching, was not supported by the data. Copyright © 1999 John Wiley & Sons, Ltd

The current study aimed to investigate in a group of nine Greek children with dyslexia (mean age 9.9 years) whether the surface and phonological dyslexia subtypes could be identified. A simple regression was conducted using printed word naming latencies and nonword reading accuracy for 33 typically developing readers. Ninety per cent confidence intervals were established and dyslexic children with datapoints lying outside the confidence intervals were identified. Using this regression-based method three children with the characteristic of phonological dyslexia (poor nonword reading), two with surface dyslexia (slow word naming latencies) and four with a mixed profile (poor nonword reading accuracy and slow word naming latencies) were identified. The children were also assessed in spelling to dictation, phonological ability, rapid naming, visual memory and multi-character processing (letter report). Results revealed that the phonological dyslexia subtype children had difficulties in tasks of phonological ability, and the surface subtype children had difficulties in tasks of multi-character simultaneous processing ability. Dyslexic children with a mixed profile showed deficits in both phonological abilities and multi-character processing. In addition, one child with a mixed profile showed a rapid naming deficit and another showed a difficulty in visual memory for abstract designs. Overall the results confirm that the surface and phonological subtypes of developmental dyslexia can be found in Greek-speaking children. They also indicate that different subtypes are associated with different underlying disorders.

We reviewed five studies that relied on the same methodologies to determine the prevalence of Phonological, Surface and Double-Deficit-Subtypes in developmental dyslexia. The proportion of these subtypes was found to vary according to the method (classical method or regression method), the measure (accuracy or processing time), the dyslexics’ language (English or French) and their chronological age. Only two results appeared consistently across the studies. First, with the classical method, and as compared to chronological age controls, most of the dyslexics appeared to suffer from a double deficit. Second, with the regression method, and as compared to reading level controls, the surface profile, though not the phonological profile, almost disappeared, thus suggesting that only the latter corresponds to a developmental deviance. In addition, in the sole study in which both accuracy and processing time were taken into account, in the comparison with reading level controls, only the phonological skills of both the phonological and the surface dyslexics were found to be impaired, either in accuracy or in processing time. These results are more in line with the hypothesis that a phonological deficit is at the core of developmental dyslexia, than with the idea that a clear dissociation exists between surface and phonological profiles.

A computational exploration of double dissociations: modes of processing instead of components of processing

Sensitivity to voicing similarity in printed stimuli: effect of a training programme in dyslexic children

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).

Varieties of Developmental Reading Disorder: Genetic and Environmental Influences

It has been suggested that auditory and visual sequential processing deficits contribute to phonological disorders in developmental dyslexia. As an alternative explanation to a phonological deficit as the proximal cause for reading disorders, the visual attention span hypothesis (VA Span) suggests that difficulties in processing visual elements simultaneously lead to dyslexia, regardless of the presence of a phonological disorder. In this study, we assessed whether deficits in processing simultaneously displayed visual or auditory elements is linked to dyslexia associated with a VA Span impairment. Sixteen children with developmental dyslexia and 16 age-matched skilled readers were assessed on visual and auditory search tasks. Participants were asked to detect a target presented simultaneously with 3, 9, or 15 distracters. In the visual modality, target detection was slower in the dyslexic children than in the control group on a “serial” search condition only: the intercepts (but not the slopes) of the search functions were higher in the dyslexic group than in the control group. In the auditory modality, although no group difference was observed, search performance was influenced by the number of distracters in the control group only. Within the dyslexic group, not only poor visual search (high reaction times and intercepts) but also low auditory search performance (d′) strongly correlated with poor irregular word reading accuracy. Moreover, both visual and auditory search performance was associated with the VA Span abilities of dyslexic participants but not with their phonological skills. The present data suggests that some visual mechanisms engaged in “serial” search contribute to reading and orthographic knowledge via VA Span skills regardless of phonological skills. The present results further open the question of the role of auditory simultaneous processing in reading as well as its link with VA Span skills.

Cerebellar symmetry in dyslexics

Impaired activation of the phonological lexicon: Effects upon oral reading

Neuropsychological and developmental differences in reading have long informed visual word recognition theories. For instance, identification of whole-word readers (i.e., phonological dyslexics, Chinese-style readers) and part-word readers (i.e., surface dyslexics, Phoenician-style readers) has constrained visual word recognition theories. The influence of variability in normal readers’ cognitive abilities on visual word recognition is yet to be explored. Differences in visual and attentional processes, long- and short-term memory, verbal and nonverbal cognitive ability, and auditory and phonological processing could influence lexical processing, which should constrain such theories. We describe the Warwick Oral Reading Differences project, which seeks to relate these factors to the strength of lexical effects on the response times typically observed in normal adult naming experiments (i.e., word frequency, length, neighborhood size, regularity, and consistency) to further constrain the interpretation of these effects and, thus, model development. Findings from the project are presented.

Reading and related skills in Grades 6, 7, 8 and 9: French normative data from EVALEC

The present paper presents data from seven developmental dyslexics who exhibit the profile of abilities which can be described as “phonological” dyslexia. Three of the cases, all children, were of low reading age; four cases, one of which was an adult, had reading ages above ten years. Tests of reading, spelling and auditory processing revealed a range of phonological deficits amongst the dyslexics when they were compared with normal readers matched for RA. However, there were individual differences, and some cases were more prototypical than others. Variability within the dyslexic sample highlights difficulties for their classification as phonological dyslexics. It is argued that a more useful approach is to consider their difficulties within a developmental framework in which phonological deficits hinder and may alter the course of literacy development.