Remediating the core deficits of developmental reading disability: a double-deficit perspective

The double-deficit hypothesis (Wolf, 1997; Wolf & Bowers, 1999, this issue) contends that deficits in phonological awareness and deficits in visual naming speed represent two independent causal impediments to reading acquisition for children with developmental reading disabilities (RD). One hundred and sixty-six children with severe RD from 7 to 13 years of age were classified into three deficit subgroups according to a double-deficit framework. A total of 140 children with RD, 84% of the sample, were classified; 54% demonstrated a double deficit (DD), 22% a phonological deficit only (PHON), and 24% a visual-naming speed deficit only (VNS). Diagnostic test profiles highlighted the joint contributions of the two core deficits in depressing written language acquisition. The children in the DD group were more globally impaired than those in the other subgroups, and the VNS group children were the highest achieving and most selectively impaired readers. Following 35 hours of word identification training, sizable gains and significant generalization of training effects were achieved by all subgroups. A metacognitive phonics program resulted in greater generalized effects across the domain of real English words, and a phonological training program produced superior outcomes within the phonological processing domain. The greatest non-word reading gains were achieved by children with only phonological deficits.     

The double-deficit hypothesis: a comprehensive analysis of the evidence

The double-deficit hypothesis of developmental dyslexia proposes that deficits in phonological processing and naming speed represent independent sources of dysfunction in dyslexia. The present article is a review of the evidence for the double-deficit hypothesis, including a discussion of recent findings related to the hypothesis. Studies in this area have been characterized by variability in methodology--how dyslexia is defined and identified, and how dyslexia subtypes are classified. Such variability sets limitations on the extent to which conclusions may be drawn with respect to the double-deficit hypothesis. Furthermore, the literature is complicated by the persistent finding that measures of phonological processing and naming speed are significantly correlated, resulting in a statistical artifact that makes it difficult to disentangle the influence of naming speed from that of phonological processing. Longitudinal and intervention studies of the double-deficit hypothesis are needed to accumulate evidence that investigates a naming speed deficit that is independent of a phonological deficit for readers with dyslexia. The existing evidence does not support a persistent core deficit in naming speed for readers with dyslexia.     

The digit naming speed test: Its power and incremental validity in identifying children with specific reading disabilities

This paper presents two studies, both of which address the question of whether a test that measures the automaticity with which digits can be named could be useful as part of a diagnostic battery to assess reading disabilities. In the first study, the Digit Naming Speed Test significantly differentiated elementary-school boys who were disabled readers from age-matched boys reading at appropriate grade levels, correctly classifying 83.3% of the children. In the second study, the Digit Naming Speed Test accounted for a significant portion of the word recognition variance of nondisabled readers over and above that portion accounted for by general intelligence as measured by the WISC-R. Taken together, these studies indicate that the Digit Naming Speed Test has the potential to contribute significantly to the diagnostic process.     

Relationship of rapid automatized naming and phonological awareness in early reading development: implications for the double-deficit hypothesis

It is widely accepted that deficits in phonological awareness skills are related to reading difficulties. Recently, another source of reading difficulty has been identified that involves naming speed, and combined impairments in phonological skills and naming speed will produce more severe reading deficits than single deficits in either of these cognitive skills. The purpose of this study was to investigate the consequences of grouping children based on the presence or absence of deficits in these skills. We demonstrate that the greater severity of reading impairment found in children with a double deficit could be due in part to a statistical artifact caused by grouping children based on their performance on two correlated continuous variables. This artifact also makes it difficult to establish the relative impact of deficits in naming speed on reading ability independent of deficits in phonological awareness.     

Naming speed and effortful and automatic inhibition in children with arithmetic learning disabilities

We report a two-year longitudinal study aimed at investigating the rate of access to numerical and non-numerical information in long-term memory and the functioning of automatic and effortful cognitive inhibition processes in children with arithmetical learning disabilities (ALDs). Twelve children with ALDs, of age 9.3 years, and twelve gender–age-matched controls were involved in the study. Rate of access was measured through digit- and letter-naming tasks, automatic cognitive inhibition was measured using a negative priming paradigm, and effortful cognitive inhibition was measured rating intrusion errors in a working memory task. Children with ALDs suffered from a deficit in the speed of activating both numerical and non-numerical information from long-term memory and in effortful inhibition mechanisms. No evidence for dysfunction of the automatic inhibition processes was found.     

Testing the double-deficit hypothesis in an adult sample

The double-deficit hypothesis of dyslexia posits that reading deficits are more severe in individuals with weaknesses in phonological awareness and rapid naming than in individuals with deficits in only one of these reading composite skills. In this study, the hypothesis was tested in an adult sample as a model of reading achievement. Participants were parents of children referred for evaluation of reading difficulties. Approximately half of all participants reported difficulty learning to read in childhood and a small subset demonstrated ongoing weaknesses in reading. Structural equation modeling results suggest that the double-deficit hypothesis is an accurate model for understanding adult reading achievement. Better reading achievement was associated with better phonological awareness and faster rapid automatized naming in adults. Posthoc analyses indicated that individuals with double deficits had significantly lower reading achievement than individuals with single deficits or no deficits.     

Depression and learning disabilities in children: a test of an hypothesis

Performance-Verbal IQ discrepancy scores are compared for 27 depressed and 15 nondepressed children all of whom experienced learning difficulties. Brumbach (1985) reported a significant association between depression and Performance IQ deficits for children with learning difficulties. In contrast to Brumbach's finding, no difference was observed in Performance IQ deficit between depressed and nondepressed children in the current study. Moreover, only 10% of depressed children showed such a deficit. This result differed significantly from Brumbach's findings (34%). Implications of these results are discussed within the context of nascent interest in the relationship between depression and learning disabilities.     

Evaluation of the double-deficit hypothesis subtype classification of readers in Spanish

The double-deficit hypothesis acknowledges both phonological processing deficits and serial naming speed deficits as two dimensions associated with reading disabilities. The purpose of this study was to examine these two dimensions of reading as they were related to the reading skills of 29 Spanish average readers and poor readers (mean age 9 years 7 months) who met the criteria for either single phonological deficit (PD), double deficit (DD), or no deficit. DD children were the slowest readers and had the weakest orthography processing skills. No significant differences were found between PD and DD groups on word and pseudoword reading. Word reading and reading comprehension skills were average or above average in the three studied groups. As in previous studies in transparent orthographies, word reading was not a salient problem for Spanish poor readers, whereas for the DD group, reading speed and orthographic recognition skills were significantly affected.     

The locus of so-called IQ test results in reading disabilities

It would appear the question of relevance of IQ in the assessment and remediation of children with RD is not quite the relevant question to ask, if only traditional intelligence tests are the focus. From the psychoeducational point of view of refining diagnosis, and from the administrative perspective of accountability, it would be helpful to accept a threshold of something like an IQ of 85 as the lower bound in defining learning or reading disabilities. A discrepancy from this threshold as derived from regression analysis or other more refined analyses and taking into account varying reliabilities, intercorrelations, and standard errors of measurement of different measuring instruments may constitute a learning or reading disability. How discrepant the aptitude-achievement should be to constitute a "significant" difference is a function of, among other factors, the material and human resources available to any particular school system. Leong (1987) has made suggestions for essentially a two-stage assessment leading to more refined diagnosis with the use of well-standardized group tests and teachers' estimates for the first stage (assessment) and more refined individual tests to diagnose those showing discrepant aptitude-learning performance in the border-zone. The rationale is that all those children requiring special services are so served and those in the uncertainty region must be carefully diagnosed so as to minimize so-called "misfits" in accordance with signal detection principles. It should be noted that the diagnosis of learning or reading disabilities can never be exact, even with the use of reliable and valid test instruments, and the "fuzzy set" approach should apply to the process (Horvath, Kass, & Ferrell, 1980).(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurodevelopmental characteristics of children with learning impairments classified according to the double-deficit hypothesis

The double-deficit model has been examined primarily in relation to reading. We investigated whether children classified according to the double-deficit model would exhibit differences in other neuropsychological domains. Children referred for learning problems (N = 188), ages 7 to 11, were classified by double-deficit subtype. Only three of the four groups predicted by the model could be identified. There were no group differences in IQ or attention problems. The three groups showed different neuropsychological profiles, involving functional domains other than reading and language. Differences also emerged in nonverbal low-level information processing. The double-deficit group was generally most severely affected. The double-deficit groupings identify children with different neuropsychological profiles and variation in the efficiency of basic online information processing, extending beyond the oral and written language domain.     

Investigating the effects of a game-based approach in teaching word recognition and spelling to students with reading disabilities and attention deficits

The purpose of this small-scale exploratory study was to examine the effects of using a game-based instructional approach to teach word recognition and spelling to Grade 6 students with reading disabilities (RD) and attention deficit disorders. Treatment and comparison groups were formed. The students were placed in either a traditional spelling group or an alternate game group. Different measures of phonological awareness, phonological memory and rapid naming as well as the word recognition and spelling subtests were administered to six students with RD and attention deficits. The study results indicate that students in the game-based approach outperformed students in the traditional, text-based spelling programs. In addition, the remediation of specific deficit subskills was possible through a game-based approach. Rapid naming, word recognition and spelling subtest results all improved through this method, with rapid naming improving the most. The study provides evidence for marked improvement in engaging behavior as well as literacy skills through alternate instructional methodologies.     

Evaluation of the double-deficit hypothesis in college students referred for learning difficulties

The present study explored the double-deficit hypothesis (DDH) in a sample of 146 college students with and without reading disabilities (RD). The results indicated that although both phonological awareness (PA) and visual naming speed (VNS) contributed to performance on measures of decoding and comprehension, their relative contribution was influenced both by the nature of the stimulus (word vs. nonword vs. text) and by the conditions of the task (timed vs. untimed). Similar results were obtained using an individual differences approach, or when between-group comparisons were made of individuals with deficits in PA or VNS. The relative representation of DDH subgroups in groups of adults with RD varied based on the classification criteria used to define RD. These results support the DDH, extend its applicability to adults, and have implications for diagnostic decision making.     

Adults with reading disabilities: converting a meta-analysis to practice

This article reviews the results of a meta-analysis of the experimental published literature that compares the academic, cognitive, and behavioral performance of adults with reading disabilities (RD) with average achieving adult readers. The meta-analysis shows that deficits independent of the classification measures emerged for adults with RD on measures of vocabulary, math, spelling, and specific cognitive process related to naming speed, phonological processing, and verbal memory. The results also showed that adults with high verbal IQs (scores > 100) but low word recognition standard scores (< 90) yielded greater deficits related to their average reading counterparts when compared to studies that included adults with RD with verbal IQ and reading scores in the same low range. Implications of the findings related to assessment and intervention are discussed.     

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.

     

Why the timing deficit hypothesis does not explain reading disability in adults

It has been proposed that the phonological coredeficit that is linked to reading failure hasas its underlying cause a deficit in temporalprocessing. In a multivariate investigationdesigned to examine the temporal processingdeficit hypothesis, thirty reading-disabled(RD) adults, thirty-two normally achievingadults and thirty-one normally achievingchildren (reading-level controls) wereadministered a comprehensive battery thatincluded a wide range of timing tasks, inaddition to reading and phonological measures. Although adults with RD displayed overallperformance that was below that of normallyachieving adults on most of the timing tasks,their performance was not differentiallyinfluenced by rate of stimulus presentation. Although the RD adults displayed the typicalpattern of impaired phonological awareness andpseudoword reading relative to reading-levelmatched children, the reading-disabled adultsoutperformed the children on the timing tasks. Finally, with the exception of continuousnaming, the timing tasks shared little variancewith phonological sensitivity and contributedlittle unique variance to word reading. Although these findings undermine the timingdeficit hypothesis, they do provide evidencefor the involvement of naming deficits inreading disability.     

Dyslexia in adults: Evidence for deficits in non-word reading and in the phonological representation of lexical items

Difficulties in reading and language skills which persist from childhood into adult life are the concerns of this article. The aims were twofold: (1) to find measures of adult reading processes that validate adults’ retrospective reports of difficulties in learning to read during the school years, and (2) to search for indications of basic deficits in phonological processing that may point toward underlying causes of reading difficulties. Adults who reported a history of difficulties in learning to read (n=102) were distinctly disabled in phonological coding in reading, compared to adults without similar histories (n=56). They were less disabled in the comprehension of written passages, and the comprehension disability was explained by the phonological difficulties. A number of indications were found that adults with poor phonological coding skills in reading (i.e., dyslexia) have basic deficits in phonological representations of spoken words, even when semantic word knowledge, phonemic awareness, educational level, and daily reading habits are taken into account. It is suggested that dyslexics possess less distinct phonological representations of spoken words. This research was supported by a grant from the Danish Research Council to the first author.