Reaction time variability associated with reading skills in poor readers with ADHD

Intraindividual Variability in Attention-Deficit/Hyperactivity Disorder: An Ex-Gaussian Approach

Higher intraindividual variability (IIV) of response times is consistently noted in children with attention-deficit/hyperactivity disorder (ADHD). The current study investigated whether an ex-Gaussian estimate of IIV in children ages 6-13 years-old could differentiate between children with and without ADHD. Children completed a computerized go/no-go task to estimate trial-by-trial IIV and a continuous performance test (CPT) to estimate inattention and hyperactivity/impulsivity. Parents completed questionnaires assessing inattention and hyperactive/impulsive behaviors. IIV, commission errors, and attention problems as rated by parents were significantly greater in the ADHD group. Groups did not differ on errors of omission, but IIV was predictive of omission errors and parent ratings of inattention and hyperactivity/impulsivity. IIV predicted group membership (ADHD vs Control) whereas errors of omission did not. However, IIV did not improve diagnostic accuracy when parent ratings were used, such that parent ratings were superior at determining diagnosis. Current results support the use of IIV, based on the ex-Gaussian approach, as an objective measure of attention problems over omission errors on sustained attention CPT-type tasks. Additionally, while parent ratings of attention impairment remain the best predictor of ADHD diagnostic status, IIV may be helpful in determining when further assessment is required in the absence of those ratings.

An Objective Assessment of Effect of Stimulants on Attention in Individuals With ADHD

INTRODUCTION

Currently, assessing ADHD treatment response to stimulants relies on rating scales and subjective questionnaires and sometimes a CPT. Such tools fall short of objective, quantifiable measurement of effect, especially in natural settings and can result in inconsistent treatment.

METHOD

We report results from two studies using a novel proof-of-concept approach. A preliminary trial of 10 individuals used a high-fidelity eye tracker; a second study of 100 individuals used webcams at the participants' homes.

RESULTS

Both studies evaluated stimulant effect using reading behavior analysis, being an ADHD symptom that stimulants affect and a major symptom patients want to improve. Both showed a significant change in reading behavior related to medication state, suggesting a clear, objective measure of stimulant effect.

CONCLUSION

Using ubiquitous hardware, investigators created a user-friendly treatment assessment platform where individuals can collect their own objective data within minutes in any setting where they have access to a web camera and computer.

Executive functions underlie word reading and reading fluency in Chinese children with attention deficit/hyperactivity disorder, reading disabilities, and comorbid attention deficit/hyperactivity disorder and reading disabilities

The current study examined the executive function (EF) deficits and their roles in reading in one hundred and four Cantonese-speaking children with typical development, reading disabilities (RD), ADHD, and comorbid ADHD and RD (ADHD + RD). Children's EF and reading skills were measured. Analysis of variance results showed that all children with disorders manifested deficits in verbal and visuospatial short-term and working memory and behavioral inhibition. Moreover, children with ADHD and ADHD + RD also exhibited deficits in inhibition (IC and BI) and cognitive flexibility. These findings demonstrated that the EF deficits in Chinese children with RD, ADHD, and ADHD + RD are similar to those in their counterparts using alphabetic languages. However, children with ADHD + RD displayed more severe deficits in visuospatial working memory compared to children with RD and ADHD, which was inconsistent with that observed in children using alphabetic languages. Regression analysis results showed that verbal short-term memory was a significant predictor for both word reading and reading fluency in children with RD and ADHD + RD. Moreover, behavioral inhibition significantly predicted reading fluency in children with ADHD. These findings also agreed with previous studies. Collectively, the results of the current study showed that the EF deficits and their roles in reading found in Chinese children with RD, ADHD, and ADHD + RD are mainly consistent with children using alphabetic languages. However, more studies are still needed to confirm these findings, especially comparing the severity of working memory among these three disorders.

The N400 in readers with dyslexia: A systematic review and meta-analysis

This systematic review and meta-analysis aimed to assess whether (i) significant differences exist in the N400 response to lexico-semantic tasks between typically developing (TD) readers and readers with dyslexia, and (ii) whether these differences are moderated by the modality of task presentation (visual vs. auditory), the type of task, age, or opaque orthography (shallow and transparent alphabets vs Chinese morpho-syllabary). Twenty studies were included in the meta-analysis, and the analysis did not demonstrate strong evidence of publication bias. An overall effect size of Hedge's g = 0.66, p < .001, was found between typically developing readers and readers with dyslexia. All moderators were found to be significant; larger effects were associated with visual modality (g = 0.692, p < .001), semantically incongruent sentence tasks (g = 0.948, p < .001), pseudowords/characters tasks (g = 0.971, p < .001), and orthography [Chinese (g = 1.015, p < .001) vs. alphabets (g = 0.539, p < .001)]. Analysis of reaction time showed Hedge's g = 1.613, p < .001. Results suggest that the N400 reliably differentiated between typically developing readers and readers with dyslexia. Implications for future research and practice are discussed.

Examining reaction time variability on the stop-signal task in the ABCD study

OBJECTIVE

Reaction time variability (RTV) has been estimated using Gaussian, ex-Gaussian, and diffusion model (DM) indices. Rarely have studies examined interrelationships among these performance indices in childhood, and the use of reaction time (RT) computational models has been slow to take hold in the developmental psychopathology literature. Here, we extend prior work in adults by examining the interrelationships among different model parameters in the ABCD sample and demonstrate how computational models of RT can clarify mechanisms of time-on-task effects and sex differences in RTs.

METHOD

This study utilized trial-level data from the stop signal task from 8916 children (9-10 years old) to examine Gaussian, ex-Gaussian, and DM indicators of RTV. In addition to describing RTV patterns, we examined interrelations among these indicators, temporal patterns, and sex differences.

RESULTS

There was no one-to-one correspondence between DM and ex-Gaussian parameters. Nonetheless, drift rate was most strongly associated with standard deviation of RT and tau, while nondecisional processes were most strongly associated with RT, mu, and sigma. Performance worsened across time with changes driven primarily by decreasing drift rate. Boys were faster and less variable than girls, likely attributable to girls' wide boundary separation.

CONCLUSIONS

Intercorrelations among model parameters are similar in children as has been observed in adults. Computational approaches play a crucial role in understanding performance changes over time and can also clarify mechanisms of group differences. For example, standard RT models may incorrectly suggest slowed processing speed in girls that is actually attributable to other factors.

Relationships between cognition and literacy in children with attention-deficit/hyperactivity disorder: A systematic review and meta-analysis

Evidence suggests that cognitive and literacy difficulties are common for children with Attention-Deficit/Hyperactivity Disorder (ADHD). The current systematic review and meta-analysis investigated the relationship between cognition and literacy in children with ADHD. Ten thousand and thirty-eight articles were screened against the inclusion criteria and six eligible studies were retained for final review. Where two or more studies used comparable measures of cognition and literacy, a meta-analysis of the relationship between these measures was undertaken. A narrative synthesis of all included studies was also completed. There were medium effect sizes between working memory and aspects of reading, and small effect sizes between processing speed and reading. Inhibition and attention had differential relationships with aspects of literacy with varying effect sizes. This systematic review demonstrates differential relationships between aspects of literacy and cognition in children with ADHD. Further examination of these relationships is warranted to support intervention development.

Visual noise effect on reading in three developmental disorders: ASD, ADHD, and DD

Background and aims

Developmental disorders such as Autism Spectrum Disorder (ASD), Attention Deficit Hyperactivity Disorder (ADHD), and Developmental Dyslexia (DD) are reported to have more visual problems, oral language difficulties, and diminished reading skills in addition to their different diagnostic features. Moreover, these conditions also have increased internal noise and probably an impaired ability of external noise filtering. The aim of the present study was to compare the reading performance of these groups in the presence of external visual noise which disrupts the automatic reading processes through the degradation of letters.

Methods

Sixty-four children and adolescents in four groups, ASD, ADHD, DD, and TD, participated in the study. Two types of stimuli were used - unrelated words and pseudowords. The noise was generated by exchanging a fixed number of pixels between the black symbols and the white background distorting the letters. The task of the participants was to read aloud the words or pseudowords. The reading time for a single letter string, word or pseudoword, was calculated, and the proportion of errors was assessed in order to describe the reading performance.

Results

The results obtained showed that the reading of unrelated words and pseudowords differs in the separate groups of participants and is affected differently by the added visual noise. In the no-noise condition, the group with TD had the shortest time for reading words and short pseudowords, followed by the group with ASD, while their reading of long pseudowords was slightly slower than that of the ASD group. The noise increase evoked variations in the reading of groups with ASD and ADHD, which differed from the no-noise condition and the control group with TD. The lowest proportion of errors was observed in readers with TD. The reading performance of the DD group was the worst at all noise levels, with the most prolonged reading time and the highest proportion of errors. At the highest noise level, the participants from all groups read the words and pseudowords with similar reading speed and accuracy.

Conclusions

In reading words and pseudowords, the ASD, ADHD, and DD groups show difficulties specific for each disorder revealed in a prolonged reading time and a higher proportion of errors. The dissimilarity in reading abilities of the groups with different development is most evident when the accuracy and reading speed are linked together.

Implications

The use of noise that degrades the letter structure in the present study allowed us to separate the groups with ASD, ADHD, and DD and disclose specifics in the reading process of each disorder. Error type analysis may provide a basis to improve the educational strategies by appropriately structuring the learning process of children with TD, ASD, ADHD, and DD.

The Effects of Choice on the Reading Comprehension and Enjoyment of Children with Severe Inattention and no Attentional Difficulties

It has been proposed that enhancing motivation supports the learning of children with Attention Deficit Hyperactivity Disorder (ADHD). Less is known if inattentive children with no ADHD diagnosis may similarly benefit, when being motivated to engage in an academic task. Using a repeated-measures design, this study investigated the effects of text choice as an intrinsic motivator on the reading comprehension and enjoyment of Year 4 children attending mainstream primary schools (N = 92; aged 8–9 years; 48 boys); comparing those with no attentional difficulties and severe inattention. We hypothesized that 1) choice would increase reading comprehension and enjoyment 2) choice would increase the reading comprehension and enjoyment of children both with severe inattention and no attentional difficulties 3) choice effects would be significantly greater for children with severe inattention than those with no attentional difficulties. Children participated in a reading intervention that included a Choice (experimental) and a No Choice (control) condition. Child inattention was measured via a Virtual Reality Continuous Performance Task (Omission errors, Reaction Time Variability) and Teacher Ratings. Choice significantly increased reading comprehension, but not enjoyment compared with no choice. Choice improved the reading comprehension of children with both severe inattention and no attentional difficulties. Choice did not benefit the reading of severely inattentive children more than that of children with no attentional difficulties. These findings underline the educational benefits of choice for young readers both with severe inattention and no attentional difficulties, which are further discussed drawing on existing theory and research.

A preliminary investigation of reaction time variability in relation to social functioning in children evaluated for ADHD

Reaction time variability (RTV) is a ubiquitous phenomenon in Attention-Deficit/Hyperactivity Disorder (ADHD). Few studies have examined RTV in relation to functional outcomes such as social impairment in children with ADHD. In this exploratory study, we investigated whether RTV is associated with social functioning in children at risk for ADHD. Specifically, we explored the association between RTV (tau derived from correct go trials of a Stop-Signal task) and social functioning in 198 children ages 7-12 years referred for an ADHD evaluation. Social functioning measures included child and/or parent ratings of social competence, aggression, social problems, and impairment in relationships. In regression analyses that also included Oppositional Defiant Disorder symptoms and sex, higher RTV was significantly associated with lower ratings of social competence, and higher proactive/reactive aggression ratings on the child self-report measures. RTV was not significantly associated with parent report of social functioning or relationship impairment. This study provides preliminary evidence that RTV may be associated with social functioning in children at risk for ADHD. We propose that lapses of attention affecting cognitive control may also negatively impact social information processing thereby affecting social functioning. Replication is warranted and longitudinal studies are needed to investigate whether RTV predicts social dysfunction in ADHD.

The Effects of ADHD Treatment and Reading Intervention on the Fluency and Comprehension of Children with ADHD and Word Reading Difficulties: A Randomized Clinical Trial

Many students with reading difficulties and disabilities (RD) also have Attention Deficit/Hyperactivity Disorder (ADHD). This randomized clinical trial compared the effects of ADHD treatment alone (medication, parent training), intensive reading intervention alone, and their combination on the reading fluency and comprehension of students with both disorders. Students with ADHD and RD were randomly assigned to receive (a) Reading Intervention only (n=74), (b) ADHD Treatment only (n=78), or (c) simultaneous Combined ADHD and RD Treatment (n=70). For phonemic decoding fluency, the Reading Intervention group and the Combined Treatment group both had significantly better outcomes than the ADHD Treatment group, but did not differ from one another. For passage comprehension, the ADHD Treatment group had significantly better outcomes than the Reading Intervention group, while the other groups did not differ from one another. ADHD treatment may support passage comprehension in this population, while fluent decoding is best supported through intensive reading intervention.

Intraindividual variability in children is related to informant ratings of attention and executive function

Objective: Attention and executive function (EF) deficits are ubiquitous in neurodevelopmental disorders including Attention Deficit/Hyperactivity Disorder (ADHD), as are high levels of intraindividual variability (IIV). Attention and EF are typically assessed using informant ratings and objective measures; however, discrepancies between different metrics often make it difficult to fully characterize a child's attention capabilities, and IIV has been proposed as a potentially useful discriminator. Our objective was to explore the relationship between IIV, using the residualized intraindividual standard deviation (rISD) method, and informant ratings of attention and EF in a mixed pediatric sample, to determine the potential utility of IIV for aiding attention diagnostics. Another commonly used, though controversial, IIV indicator, the coefficient of variation (ICV), was calculated for comparison purposes. Method: We assessed 51 children with varying degrees of attention and EF deficits. Measures included parent and teacher responses on the Comprehensive Executive Function Inventory (CEFI) and response times (RT) on a go/no-go task, which were used to estimate IIV. Results: Mean RT, rISD, and ICV were significantly related to parent and teacher ratings of attention, though ICV showed a relatively weaker association. rISD also showed associations with parent ratings of working memory and self-monitoring, as well as teacher ratings of working memory. Conclusion: The significant, and relatively stronger, relationship between rISD and parent and teacher ratings of attention supports the use of this metric, compared to mean RT and ICV. The rISD indicator of IIV thus shows potential utility as a unique and objective measure of attention in children across various neurodevelopmental disorders and, with additional research, may prove useful for diagnosis of attention problems.

Differential effect of reading training on functional connectivity in children with reading difficulties with and without ADHD comorbidity

A comorbidity of attention deficit hyperactivity disorder (ADHD) with reading difficulties (RD) is common in children. However, children with ADHD+RD have a different reading and executive functions (EF) profile than children with RD alone. We compared the effect of an EF-based intervention on neural circuits related to EF in children with RD and those with ADHD+RD. Functional connectivity MRI data from a lexical decision task suggest that the RD-alone group showed greater improvement in EF and reading tests and greater functional connectivity between networks related to both higher-and lower-level visual processing and those related to ventral attention and dorsal attention, as well as semantic processing. Children with ADHD+RD showed greater connectivity between networks related to attention and dorsal attention and those related to visual processing and EF. Results are consistent with the Cognitive Subtype hypothesis and suggest that RD and ADHD+RD, although related behaviourally, are distinct disorders with regard to network response and connectivity during reading and after an EF-based intervention.

Profile of reading difficulties in children with attention deficit hyperactivity disorder: a literature review

ABSTRACT Purpose: to characterize the reading alterations in individuals with attention deficit hyperactivity disorder. Methods: PubMed and SciELO platforms from 2006 to 2016 with the keywords "reading" and "attention deficit hyperactivity disorder", with their equivalents in Portuguese, were searched. Results: seven hundred ninety articles were found in the two databases, of which 119 were relevant. After a full reading, twenty five articles were selected for the analysis, according to relevance and other exclusion/inclusion criteria. In 21 of the studies, individuals with attention deficit hyperactivity disorder presented worse performance in reading, as compared with their peers. Of these, 14 studies identified a delay in some skills that are important for reading: processing speed, reading accuracy, phonological awareness, comprehension and/or orthographic processing. Conclusion: these results corroborate other studies that have verified the presence of a deficit in academic performance, especially in reading skills, in individuals with attention deficit hyperactivity disorder, that may persist in their adulthood.

Novel reading index for identifying disordered reading skill development: A preliminary study

Children with ADHD are at high risk of developing a Reading Disability (RD), although the reasons remain unclear. ADHD-associated impairments, including processing speed, can complicate clinical evaluation for a co-occurring RD diagnosis. We propose a novel metric to (a) assess reading development and (b) provide an alternative method to classifying readers that may aid investigations for etiologies of RD in ADHD. Specifically, as both phonological decoding and word recognition skills are important precursors of reading fluency, we propose a new quantitative method comparing these skills after accounting for variations in perception, motor response, or processing speeds. Forty boys (14 control, 15 ADHD, 11 ADHD/ + RD) completed a lexical decision task testing decoding and another assessing word recognition. Response time data was modeled using a Drift Diffusion approach to estimate the underlying reading skills. Using these reading skill estimates, we calculated a novel Reading Tendency Index and classified participants into three reading groups (Decoders, Balanced Readers, and Sight Readers). The reading and cognitive performance of these groups were consistent with theoretical predictions and subsequently provided external validity for the novel Reading Tendency Index classification. Our findings demonstrate a potential classification tool for readers based on individual's developed, reading tendencies.

Amphetamine Modestly Improves Conners' Continuous Performance Test Performance in Healthy Adults

OBJECTIVES

Amphetamine improves vigilance as assessed by continuous performance tests (CPT) in children and adults with attention deficit hyperactivity disorder (ADHD). Less is known, however, regarding amphetamine effects on vigilance in healthy adults. Thus, it remains unclear whether amphetamine produces general enhancement of vigilance or if these effects are constrained to the remediation of deficits in patients with ADHD.

METHODS

We tested 69 healthy adults (35 female) on a standardized CPT (Conner's CPT-2) after receiving 10- or 20-mg d-amphetamine or placebo. To evaluate potential effects on learning, impulsivity, and perseveration, participants were additionally tested on the Iowa Gambling Task (IGT) and Wisconsin Card Sorting Task (WCST).

RESULTS

Participants receiving placebo exhibited the classic vigilance decrement, demonstrated by a significant reduction in attention (D') across the task. This vigilance decrement was not observed, however, after either dose of amphetamine. Consistent with enhanced vigilance, the 20-mg dose also reduced reaction time variability across the task and the ADHD confidence index. The effects of amphetamine appeared to be selective to vigilance since no effects were observed on the IGT, WCST, or response inhibition/perseveration measures from the CPT.

CONCLUSIONS

The present data support the premise that amphetamine improves vigilance irrespective of disease state. Given that amphetamine is a norepinephrine/dopamine transporter inhibitor and releaser, these effects are informative regarding the neurobiological substrates of attentional control. (JINS, 2018, 24, 283-293).

Attentional selection predicts rapid automatized naming ability in Chinese-speaking children with ADHD

Children with attention-deficit/hyperactivity disorder (ADHD) are reported to have a significantly higher risk of showing reading difficulties or disorders. Here, we aimed to identify the relationship between electroencephalographic (EEG) marker of spatial attention and reading ability in Chinese children with ADHD. First, we demonstrated that rapid automatized naming (RAN) is a strong predictor of reading ability in Chinese-speaking children. Then, EEG data of 9-to 15-year-old children with ADHD (n = 38) and typically developing (TD) controls (n = 36) were collected while the children performed a classical visual search task. Children with ADHD showed slower RAN speed than TD children. For event-related potentials (ERPs), children with ADHD showed a reduced target-evoked N2pc component, which predicted their poorer RAN performance. However, in TD children the early occipital P1 amplitude was negatively correlated with their RAN performance. The correlation between decreased N2pc and poor RAN performance in children with ADHD suggests that their reading problems may in part be due to impaired attentional selection. In contrast, in TD children, development in early visual processing co-occurs with improvements in reading ability.

Clinical and functional correlates of processing speed in pediatric Attention-Deficit/Hyperactivity Disorder: a systematic review and meta-analysis

It is well established that processing speed is negatively impacted in children and adolescents with Attention-Deficit/Hyperactivity Disorder (ADHD). Unfortunately, exactly how processing speed vulnerabilities manifest in daily functioning has not been well established. To support clinical care of youth with ADHD, it is important to better understand the functional consequences and relevant outcomes associated with processing speed deficits. This systematic review and meta-analysis sought to identify the association between processing speed and clinical or functional correlates among children or adolescents diagnosed with ADHD. A total of 409 abstracts were screened, of which, 60 full-text articles were identified as potentially relevant, and 8 of these studies met inclusion criteria. Domains evaluated across these studies included reading skills, mathematics skills, written expression, anxiety, self-appraisals of competence, and adaptive functioning. Six studies reported an association between processing speed and reading skills, allowing for meta-analysis. Processing speed difficulties among youth with ADHD appear strongly associated with several clinical and functional correlates including weaker academic skills, poorer adaptive skills, increased self-reported anxiety, and overestimates of social competence. Meta-analytic results for studies reporting the association between processing speed and reading skills indicate a medium overall weighted mean effect size (r = 0.33, 95% CI = 0.28 -0.39) with minimal heterogeneity (I² = 0.17). Clinical implications of these findings, limitations in the current knowledge base, and suggestions for future research are discussed.

Rapid automatized naming (RAN) in children with ADHD: An ex-Gaussian analysis

Children with ADHD demonstrate increased frequent "lapses" in performance on tasks in which the stimulus presentation rate is externally controlled, leading to increased variability in response times. It is less clear whether these lapses are also evident during performance on self-paced tasks, e.g., rapid automatized naming (RAN), or whether RAN inter-item pause time variability uniquely predicts reading performance. A total of 80 children aged 9 to 14 years-45 children with attention-deficit/hyperactivity disorder (ADHD) and 35 typically developing (TD) children-completed RAN and reading fluency measures. RAN responses were digitally recorded for analyses. Inter-stimulus pause time distributions (excluding between-row pauses) were analyzed using traditional (mean, standard deviation [SD], coefficient of variation [CV]) and ex-Gaussian (mu, sigma, tau) methods. Children with ADHD were found to be significantly slower than TD children (p < .05) on RAN letter naming mean response time as well as on oral and silent reading fluency. RAN response time distributions were also significantly more variable (SD, tau) in children with ADHD. Hierarchical regression revealed that the exponential component (tau) of the letter-naming response time distribution uniquely predicted reading fluency in children with ADHD (p < .001, ΔR² = .16), even after controlling for IQ, basic reading, ADHD symptom severity and age. The findings suggest that children with ADHD (without word-level reading difficulties) manifest slowed performance on tasks of reading fluency; however, this "slowing" may be due in part to lapses from ongoing performance that can be assessed directly using ex-Gaussian methods that capture excessively long response times.

Brain lateralization and self-reported symptoms of ADHD in a population sample of adults: a dimensional approach

Many clinical studies reported a compromised brain lateralization in patients with Attention-Deficit/Hyperactivity Disorder (ADHD) without being conclusive about whether the deficit existed in the left or right hemisphere. It is well-recognized that studying ADHD dimensionally is more controlled for comorbid problems and medication effects, and provides more accurate assessment of the symptoms. Therefore, the present study applied the dimensional approach to test the relationship between brain lateralization and self-reported ADHD symptoms in a population sample. Eighty-five right-handed university students filled in the Conners' Adult ADHD Rating Scales and performed a lateralization reaction time task. The task consists of two matching conditions: one condition requires nominal identification for letters tapping left hemisphere specialization (Letter Name-Identity condition) and the other one requires physical and visuospatial identification for shapes tapping right hemisphere specialization (Shape Physical-Identity condition). The letters or shapes to be matched are presented in left or right visual field of a fixation cross. For both task conditions, brain lateralization was indexed as the difference in mean reaction time between left and right visual field. Linear regression analyses, controlled for mood symptoms reported by a depression, anxiety, and stress scale, showed no relationship between the variables. These findings from a population sample of adults do not support the dimensionality of lateralized information processing deficit in ADHD symptomatology. However, group comparison analyses showed that subjects with high level of inattention symptoms close to or above the clinical cut-off had a reduced right hemisphere processing in the Shape Physical-Identity condition.

Reading performance is predicted by more than phonological processing

We compared three phonological processing components (phonological awareness, rapid automatized naming and phonological memory), verbal working memory, and attention control in terms of how well they predict the various aspects of reading: word recognition, pseudoword decoding, fluency and comprehension, in a mixed sample of 182 children ages 8–12 years. Participants displayed a wide range of reading ability and attention control. Multiple regression was used to determine how well the phonological processing components, verbal working memory, and attention control predict reading performance. All equations were highly significant. Phonological memory predicted word identification and decoding. In addition, phonological awareness and rapid automatized naming predicted every aspect of reading assessed, supporting the notion that phonological processing is a core contributor to reading ability. Nonetheless, phonological processing was not the only predictor of reading performance. Verbal working memory predicted fluency, decoding and comprehension, and attention control predicted fluency. Based upon our results, when using Baddeley’s model of working memory it appears that the phonological loop contributes to basic reading ability, whereas the central executive contributes to fluency and comprehension, along with decoding. Attention control was of interest as some children with ADHD have poor reading ability even if it is not sufficiently impaired to warrant diagnosis. Our finding that attention control predicts reading fluency is consistent with prior research which showed sustained attention plays a role in fluency. Taken together, our results suggest that reading is a highly complex skill that entails more than phonological processing to perform well.

Shared cognitive impairments and aetiology in ADHD symptoms and reading difficulties

Background

Twin studies indicate that the frequent co-occurrence of attention deficit hyperactivity disorder (ADHD) symptoms and reading difficulties (RD) is largely due to shared genetic influences. Both disorders are associated with multiple cognitive impairments, but it remains unclear which cognitive impairments share the aetiological pathway, underlying the co-occurrence of the symptoms. We address this question using a sample of twins aged 7–10 and a range of cognitive measures previously associated with ADHD symptoms or RD.

Methods

We performed multivariate structural equation modelling analyses on parent and teacher ratings on the ADHD symptom domains of inattention and hyperactivity, parent ratings on RD, and cognitive data on response inhibition (commission errors, CE), reaction time variability (RTV), verbal short-term memory (STM), working memory (WM) and choice impulsivity, from a population sample of 1312 twins aged 7–10 years.

Results

Three cognitive processes showed significant phenotypic and genetic associations with both inattention symptoms and RD: RTV, verbal WM and STM. While STM captured only 11% of the shared genetic risk between inattention and RD, the estimates increased somewhat for WM (21%) and RTV (28%); yet most of the genetic sharing between inattention and RD remained unaccounted for in each case.

Conclusion

While response inhibition and choice impulsivity did not emerge as important cognitive processes underlying the co-occurrence between ADHD symptoms and RD, RTV and verbal memory processes separately showed significant phenotypic and genetic associations with both inattention symptoms and RD. Future studies employing longitudinal designs will be required to investigate the developmental pathways and direction of causality further.