RD,ADHD, and their comorbidity from a dual route perspective

In order to achieve further insight into the comorbidity of reading disorder (RD) and attention deficit/hyperactivity disorder (ADHD), lexical processing and rapid naming were studied in RD and ADHD. The Dual Route Cascaded model postulates that lexical processing contains two parallel processes: lexical route processing and sublexical route processing. An orthographic decision task and a phonological decision task were used to measure lexical and sublexical route processing, respectively. In addition, a rapid naming task was used to compare 27 children with RD, 18 children with ADHD, 20 children with ADHD+RD, and 29 controls. RD and ADHD shared impairments in accuracy of orthographic and phonological decision making as well as in rapid naming, which suggest that RD and ADHD may be overlapping disorders that share deficits in both lexical route and sublexical route processing. RD was dissociated from ADHD by being slower in both orthographical and phonological decision making that indicates unique deficits in RD on lexical and sublexical speed.     

RD, ADHD, and their comorbidity from a dual route perspective

In order to achieve further insight into the comorbidity of reading disorder (RD) and attention deficit/hyperactivity disorder (ADHD), lexical processing and rapid naming were studied in RD and ADHD. The Dual Route Cascaded model postulates that lexical processing contains two parallel processes: lexical route processing and sublexical route processing. An orthographic decision task and a phonological decision task were used to measure lexical and sublexical route processing, respectively. In addition, a rapid naming task was used to compare 27 children with RD, 18 children with ADHD, 20 children with ADHD+RD, and 29 controls. RD and ADHD shared impairments in accuracy of orthographic and phonological decision making as well as in rapid naming, which suggest that RD and ADHD may be overlapping disorders that share deficits in both lexical route and sublexical route processing. RD was dissociated from ADHD by being slower in both orthographical and phonological decision making that indicates unique deficits in RD on lexical and sublexical speed.     

Separate brain potential characteristics in children with reading disability and attention deficit disorder: color and letter relevance effects

This experiment was on event-related potential (ERP) indicants of the selective neural processing of black vs. white and letter vs. nonletter stimuli in boys (8-12 years of age) with and without a reading disability (RD) and/or attentional deficit disorder (ADD). Selective neural processing was measured by the increase or difference in ERP amplitude in response to stimuli that were relevant as compared to irrelevant to the color or letter attention task. The 52 children that participated in the study constituted four groups: 25 normal reading children (17 without ADD and 8 with ADD), and 27 RD children (11 without ADD and 16 with ADD). ERPs were recorded over the left and right occipital, central, and frontal regions. Selective neural processing due to stimulus relevance was reduced in boys with RD as compared to normal readers. This reduced selectivity was indicated by a predominantly symmetrical reduction in the magnitude of a positive difference potential over the central regions, between 300 and 360 msec, and then by a left greater than right hemisphere reduction in the magnitude of a positive difference potential over the occipital regions, at about 400 msec. Task relevance increased the within-subject and condition variability of this occipital positive component and this effect was greater for boys without than with RD, particularly over the left hemisphere. Selective neural processing due to stimulus relevance was greater in boys with ADD as compared to those without ADD. This was indicated by an increase in the magnitude of a positive difference potential between 320 and 400 msec over the central and frontal regions and a slow, late, negative difference potential between 600 and 800 msec over the central and occipital regions. These ADD effects tended to be greater over the right than left hemisphere. The unique polarity, scalp distribution, and time course of the effects of RD as compared to ADD on ERPs to relevant stimuli clearly indicated these two disorders, in part, involve different underlying brain deficits.     

Naming Speed Performance and Stimulant Effects Indicate Effortful, Semantic Processing Deficits in Attention-Deficit/Hyperactivity Disorder

This study investigated rapid automatized naming and effects of stimulant medication in school-age children with attention-deficit/hyperactivity disorder (ADHD) with and without concurrent reading disorder (RD). Two ADHD groups (67 ADHD only; 21 ADHD + RD) and a control group of 27 healthy age-matched peers were compared on four variables: color naming speed, letter naming speed, phonologic decoding, and arithmetic computation. Discriminant function analysis (DFA) was conducted to predict group membership. The four variables loaded onto two discriminant functions with good specificity: phonologic decoding, letter naming speed, and arithmetic defined the first function; color naming speed defined the second function. Both ADHD groups were significantly slower in color naming than controls, but did not differ from one another. DFA correctly classified 96% of the control group, 91% of ADHD + RD, and 82% of ADHD only. A subset of children in the ADHD groups participated subsequently in an acute, randomized, placebo-controlled, crossover trial with three single doses (10, 25, 20 mg) of methylphenidate. Methylphenidate selectively improved color-naming speed but had no effect on the speed of naming letters or digits. These findings challenge the tenet that naming speed deficits are specific to RD and implicate naming speed deficits associated with effortful semantic processing in ADHD, which are improved but not normalized by stimulant medication.     

Short-term memory deficits in reading disabled children,in the absence of opportunity for rehearsal strategies

Two groups of reading-disabled (RD) children were compared with controls (age- and IQ-matched competent readers), on a serial running memory task. The unknown (to the subject) length of the serial lists coupled with high rates of presentation, made it impossible for the children to use systematic rehearsal strategies in this task. Both groups of RD children performed reliably worse than their controls. From the data, it is argued that the short-term memory deficits exhibited by the RD children should not be attributed to an inability to rehearse, nor to an inability to encode (recognize) items, but rather to an inability to encode serial items in the form of serial phonological patterns.     

The influence of working memory on reading growth in subgroups of children with reading disabilities

This 3-year longitudinal study determined whether (a) subgroups of children with reading disabilities (RD) (children with RD only, children with both reading and arithmetic deficits, and low verbal IQ readers) and skilled readers varied in working memory (WM) and short-term memory (STM) growth and (b) whether growth in an executive system and/or a phonological storage system mediated growth in reading performance. A battery of memory and reading measures was administered to 84 children (11-17 years of age) across three testing waves spaced 1 year apart. The results showed that skilled readers yielded higher WM growth estimates than did the RD groups. No significant differentiation among subgroups of children with RD on growth measures emerged. Hierarchical linear modeling showed that WM (controlled attention), rather than STM (phonological loop), was related to growth in reading comprehension and reading fluency. The results support the notion that deficient growth in the executive component of WM underlies RD.     

A comparison of 13-year-old boys with attention deficit and/or reading disorder on neuropsychological measures

This study compared 13 year-old-boys with attention deficit disorder (ADD) and/or reading disability (RD), and controls with neither disorder on a battery of verbal and nonverbal neuropsychological measures. The aim was to examine whether ADD was associated with a qualitatively distinct pattern of deficits compared with RD. None of the measures differentiated the boys with ADD-only from the controls; the only deficit associated with ADD was slightly lower IQ. RD, on the other hand, was associated with deficits in memory and verbal skills.The Dunedin Multidisciplinary Health and Development Research Unit is supported by the Medical Research Council of New Zealand and involves several Departments of the University of Otago. Much of the data are gathered by voluntary workers from the Dunedin community.The authors are indebted to the many people who contributions make this ongoing study possible. We wish to acknowledge the advice and help of Dr. P. A. Silva, director of the Dunedin Unit, in preparing this report.     

Effortful processing deficits in children with reading and/or attention disorders

Three groups of educationally troublesome boys were contrasted with adequate students on several tasks tapping effortful processing. The nonhyperactive reading disabled (RD) group differed both from controls and two attention deficit disorder (ADD) groups, one with and one without hyperactivity (H), on aspects of a memory task involving acoustic and semantic associations. All three clinical groups differed from controls in memory for low-imagery as opposed to high-imagery words and in computational efficiency. A stepwise regression analysis to predict reading grade level showed age and WISC-R IQ to account for 38% of the variance with an additional 28% explained by the effortful task variables (multiple R = .83). It is theorized here that attentional disorder impedes automatization of number facts; and, inasmuch as RD children receive adverse attention ratings, even if not considered hyperactive, they, as well as ADD and H/ADD boys, exhibit this deficiency.     

Direct assessment of the cognitive correlates of attention deficit disorders with and without hyperactivity

The cognitive functioning of children identified as attention deficit disorder with hyperactivity (ADD/H) was compared to that of children identified as attention deficit disorder without hyperactivity (ADD/WO). Based on information on symptoms supplied by teachers, 20 ADD/H and 15 ADD/ WO children were selected according to DSM-III criteria from a large elementaryschool learning disabilities and behavior disorders population. For comparison purposes, 16 normal children from regular classrooms were also selected. Children from all three groups were evaluated with a battery of cognitive tests. Intelligence test scores differentiated the two ADD groups, with the ADD/H children obtaining significantly lower Full Scale IQ scores than both ADD/WO and control children. In addition, ADD/H children obtained significantly lower Verbal IQ scores than ADD/WO children. Both ADD groups performed more poorly than controls on Spelling and Reading Achievement, and the ADD/WO group performed more poorly on Math Achievement. The two ADD groups took longer to complete six Stroop and rapid naming tasks than the control groups but did not differ among themselves. The ADD/WO group made more errors on a visual matching task than the controls, but neither ADD group differed from controls on the accuracy of the Stroop tasks, rapid naming tasks, measures of receptive and expressive language, visual-motor integration, or sustained visual attention. The differences between the two ADD groups were fewer than expected on the basis of previous research and are more global than specific.The assistance of John Junginger, Jason Walker, and Cynthia Jones at various stages of the project is gratefully acknowledged. Particular thanks are extended to the teachers and staff of Clarke County schools.     

Basic number processing in children with specific learning disorders: Comorbidity of reading and mathematics disorders

As well as being the hallmark of mathematics disorders, deficits in number processing have also been reported for individuals with reading disorders. The aim of the present study was to investigate separately the components of numerical processing affected in reading and mathematical disorders within the framework of the Triple Code Model. Children with reading disorders (RD), mathematics disorders (MD), comorbid deficits (RD + MD), and typically developing children (TD) were tested on verbal, visual-verbal, and nonverbal number tasks. As expected, children with MD were impaired across a broad range of numerical tasks. In contrast, children with RD were impaired in (visual-)verbal number tasks but showed age-appropriate performance in nonverbal number skills, suggesting their impairments were domain specific and related to their reading difficulties. The comorbid group showed an additive profile of the impairments of the two single-deficit groups. Performance in speeded verbal number tasks was related to rapid automatized naming, a measure of visual-verbal access in the RD but not in the MD group. The results indicate that deficits in number skills are due to different underlying cognitive deficits in children with RD compared to children with MD: a phonological deficit in RD and a deficit in processing numerosities in MD.     

Time Perception: Does It Distinguish ADHD and RD Children in a Clinical Sample?

This study used a double-dissociation design to evaluate whether children with ADHD demonstrated specific deficits relative to children with Reading Disorders. Recent theory suggests that ADHD children have deficits in time perception and working memory, whereas RD children have deficits in phonological decoding. The performance of 113 clinic-referred children aged 6-11 was examined using measures of working memory, phonological processing, and time perception. Respondents completed two time production tasks in which they were to judge when 30-s had elapsed, and another in which they were asked to estimate the duration of the Conners' CPT (CCPT). Time Perception and phonological processing variables were submitted to a 2 x 2 ANCOVA (ADHD vs. RD), covarying for age, SES, IQ, and working memory. Children with ADHD were more likely to overestimate the time taken for the CCPT than children without ADHD, but no group differences were found on the 30-s estimation tasks. Children with RD did not display deficits in time estimation, but showed deficits in auditory phonological processing. The lack of interaction effects supported an "etiological subtype" over the "phenocopy" model of ADHD and RD. No group differences were detected using the CCPT. Although our previous studies did not find an order effect for the Conners' CPT in a 1-hr battery, a fatigue effect was evident with a 1.5-hr battery. The implications for Barkley's behavioral inhibition theories (R. Barkley, 1997) are discussed.     

Co-occurring disorders: a possible key to visual perceptual deficits in children with developmental coordination disorder?

A study was conducted to examine how visual perceptual functioning in children with DCD may be influenced by co-occurring learning problems such as reading disabilities (RD) and/or attention deficit hyperactivity disorder (ADHD). Participants included seven groups of children: 27 children with DCD only, 11 with ADHD only, 14 with RD only, 63 with DCD and at least one other disorder (i.e., DCD + ADHD, DCD + RD, DCD + ADHD + RD), and 73 typically developing controls. Visual perceptual skills were assessed using the Test of Visual Perceptual Skills (TVPS) and the Rey Osterreith Complex Figure (ROCF; copy and delayed recall). Children with DCD and at least one other disorder were found to have impairments on the TVPS compared to children with DCD only, ADHD only, and typically developing controls, particularly on subtests assessing visual memory. On the ROCF, children with DCD and at least one other disorder scored significantly lower than children with ADHD only or RD only. Children with DCD plus one other disorder were then subdivided into three groups: DCD + ADHD, DCD + RD, and DCD + ADHD + RD and compared to children with DCD only, ADHD only, and RD only. Results indicated that children with DCD + ADHD + RD had significant impairments on the TVPS compared to children with DCD only and children with ADHD only. On the ROCF, children with DCD + ADHD + RD scored significantly lower than all of the groups, except the DCD+RD group. These findings suggest that DCD on its own is not associated with visual perceptual problems; rather, it is the presence of co-occurring disorders that is a possible key to visual perceptual deficits in children with DCD. The number of co-occurring disorders present with DCD is associated with the severity of the visual perceptual dysfunction. Deficits in visual memory skills appear to be a specific area of difficulty for children with DCD and co-occurring RD and/or ADHD.     

前摄抑制对儿童注意缺陷多动障碍(ADHD)和阅读障碍的言语工作记忆的影响

ADHD和阅读障碍儿童在言语工作记忆上的缺陷得到了大量研究的证实,但是二者机制并不相同,前摄抑制对工作记忆容量产生了不利的影响,主要影响的也是中央执行功能。研究将最近探测任务和n-back任务相结合,直接比较被试在最近负探测和非最近负探测条件下记忆成绩的差异,以考察前摄抑制对两种障碍言语工作记忆的影响,被试是60名障碍儿童(阅读障碍和ADHD)和17名正常儿童,年龄均在7至12岁之间。结果发现,受前摄抑制的影响,正常被试和障碍被试成绩均明显下降,具体而言,ADHD和ADHD伴随阅读障碍组成绩大幅下滑(26.44%,28.44%),程度明显高于正常儿童和阅读障碍儿童(14.62%,15.84%),后两者差异并不明显,这说明前摄抑制是影响工作记忆容量的重要因素,并且ADHD儿童更加容易受到前摄抑制的影响,这是导致其工作记忆成绩缺损的重要原因,而阅读障碍儿童能够像正常儿童一样,在一定程度上处理前摄抑制,ADHD和阅读障碍组在言语工作记忆缺损机制上存在差异。     

阅读障碍与注意缺陷多动障碍儿童的语言加工和反应抑制

阅读障碍与注意缺陷多动障碍(ADHD)高度共病,以往研究结果显示两种障碍在语言加工、执行功能等领域的缺陷既相似又不同。本研究采用语音意识测验、快速命名测验、语素意识测验和停止信号任务,以及阅读广度测验,分别考察四组被试（阅读障碍组、ADHD组、双重障碍组、正常控制组）的基础语言加工、反应抑制和言语工作记忆能力,结果发现：阅读障碍组和双重障碍组在语言加工任务上的成绩均显著差于ADHD组和正常组;ADHD组和双重障碍组在停止信号任务上的成绩显著差于阅读障碍组和正常组;所有障碍组在阅读广度测验上的成绩显著差于正常组。表明阅读障碍的特异性缺陷体现在语言加工过程上,而注意缺陷多动障碍的特异性缺陷体现在反应抑制上。这对于今后单一障碍的研究及临床诊断和干预具有重要的参考价值。     

Comorbidity of ADHD and reading disability among clinic-referred children

Of a consecutive series of 115 boys diagnosed in a university outpatient clinic as ADHD, 39% also demonstrated a specific reading disability. Pure ADHD patients were compared with mixed ADHD + RD and normal controls on a battery of cognitive and attentional measures. The aim was to determine whether a distinct pattern of deficits would distinguish the groups. Both ADHD subgroups performed significantly worse than controls on measures of sequential memory and attentional tasks involving impulse control andplanful organization. Only ADHD+RD boys differed from controls on measures or rapid word naming and vocabulary. The reuslts are discussed within the framework of an automatic versus effortful information-processing model.     

Memory Functioning in Children with Reading Disabilities and/or Attention Deficit/Hyperactivity Disorder: A Clinical Investigation of their Working Memory and Long-Term Memory Functioning

We examined memory functioning in children with reading disabilities (RD), Attention deficit/hyperactivity disorder (ADHD), and RD/ADHD using a clinic sample with a clinical instrument: the Children's Memory Scale, enhancing its generalizability. Participants included 23 children with RD, 30 with ADHD, 30 with RD/ADHD, and 30 controls. Children with RD presented with reduced verbal short-term memory (STM) but intact visual STM, central executive (CE), and long-term memory (LTM) functioning. Their deficit in STM appeared specific to tasks requiring phonetic coding of material. Children with ADHD displayed intact CE and LTM functioning but reduced visual-spatial STM, especially when off stimulant medication. Children with RD/ADHD had deficits consistent with both disorders.     

How Distinctive are ADHD and RD? Results of a Double Dissociation Study

The nature of the comorbidity between Attention-Deficit/Hyperactivity Disorder (ADHD) and Reading Disability (RD) was examined using a double dissociation design. Children were between 8 and 12 years of age and entered into four groups: ADHD only (n = 24), ADHD+RD (n = 29), RD only (n = 41) and normal controls (n = 26). In total, 120 children participated in the study; 38 girls and 82 boys. Both ADHD and RD were associated with impairments in inhibition and lexical decision, although inhibition and lexical decision were more severely impaired in RD than in ADHD. Visuospatial working memory deficits were specific to children with only ADHD. It is concluded that there was overlap on lexical decision and to a lesser extent on inhibition between ADHD and RD. In ADHD, impairments were dependent on IQ, which suggest that the overlap in lexical decision and inhibition is different in origin for ADHD and RD. The ADHD only group was specifically characterized by deficits in visuospatial working memory. Hence, no double dissociation between ADHD and RD was found on executive functioning and lexical decision.     

Processing Speed Deficits in Attention Deficit/Hyperactivity Disorder and Reading Disability

The goal of the current study was to test whether deficits in processing speed (PS) may be a shared cognitive risk factor in reading disability (RD) and Attention Deficit/Hyperactivity Disorder (ADHD), which are known to be comorbid. Literature on ADHD and RD suggests that deficits on tasks with a speeded component are seen in both of these disorders individually. The current study examined a wide range of speeded tasks in RD, ADHD, comorbid RD+ADHD, and a control group to test whether RD and ADHD have similar profiles of PS deficits, and whether these deficits are shared by the two disorders. The results suggest that a general PS deficit exists in both clinical groups compared to controls, although children with RD demonstrate greater PS deficits than children with ADHD. Two tests (underadditivity and partial correlations) were conducted to test whether these PS deficits are shared. Since we found that PS deficits were underadditive in the comorbid group and that partialling PS reduced the correlation between RD and ADHD, it appears that PS is a shared cognitive risk factor that may help explain the comorbidity of these two disorders.     

Paired associate learning in Chinese children with dyslexia

A total of 82 Chinese 11- and 12-year-olds with and without dyslexia were tested on four paired associate learning (PAL) tasks, phonological awareness, morphological awareness, rapid naming, and verbal short-term memory in three different experiments. Experiment 1 demonstrated that children with dyslexia were significantly poorer in visual-verbal PAL than nondyslexic children but that these groups did not differ in visual-visual PAL performance. In Experiment 2, children with dyslexia had more difficulties in transferring rules to new stimuli in a rule-based visual-verbal PAL task as compared with children without dyslexia. Long-term retention of PAL was not impaired in dyslexic children across either experiment. In Experiment 3, rates of visual-verbal PAL deficits among children with dyslexia were all at or above 39%, the highest among all cognitive deficits tested. Moreover, rule-based visual-verbal PAL, in addition to morphological awareness and rapid naming ability, uniquely distinguished children with and without dyslexia even with other metalinguistic skills statistically controlled. Results underscore the importance of visual-verbal PAL for understanding reading impairment in Chinese children.     

Language Abilities in Children with Attention Deficit Hyperactivity Disorder, Reading Disabilities, and Normal Controls

Research has demonstrated a high prevalence of language impairments (LI) and reading disabilities (RD) in children with attention deficit hyperactivity disorder (ADHD). Since RD is also associated with LI, it is unclear whether the language impairments are specific to ADHD or associated with comorbid RD. The language abilities of ADHD children with and without RD were investigated in a task requiring recall of a lengthy narrative, and in tests assessing knowledge of the semantic aspects of language. The study was conducted with 50 boys—14 ADHD, 14 ADHD + RD, 8 RD, and 14 normal controls, aged 7 to 11. Children with ADHD (ADHD-only, ADHD + RD) exhibited difficulties in organizing and monitoring their story retelling. Children with RD (RD-only, ADHD + RD) demonstrated deficits in receptive and expressive semantic language abilities on the language processing tests. The comorbid group (ADHD + RD) exhibited the deficits of both ADHD and RD children. The deficiencies of ADHD children are consistent with higher-order executive function deficits while the deficits of RD children are consistent with deficits in the basic semantics of language processing.