Studying neurodevelopmental disorders and their impact on learning

Featured Research

RARC conducts research about neurodevelopmental disorders, the measures used to test for these disorders, and the recommended accommodations and interventions required to allow for equal access and participation in the post-secondary learning environment.

In-Person (FTF) and In-Home (TNP) Assessments With Youth With Neuro-developmental Disorders: What’s the Difference?

Julia Moreau, Beth Pollock & Allyson G. Harrison -- Canadian Journal of School Psychology, 2023

Due to the COVID-19 pandemic, the field shifted from seeing clients face-to-face (FTF) for psychoeducational assessments to conducting evaluations virtually via teleneuropsychology (TNP) in the client’s own home. The study sought to determine the equivalence of testing using both modalities. Results suggest generally equivalent results, with a few caveats.

Read "In-Person and In-Home Teleneuropsychological Assessments With Youth With Neurodevelopmental Disorders: What’s the Difference?" Article (PDF 197KB)

Ability of Self-Report Methods to Accurately Diagnose Attention Deficit Hyperactivity Disorder

Allyson G. Harrison and Melanie J. Edwards--Journal of Attention Disorders, 2023

Rating scales or interview-based screeners are commonly used to evaluate ADHD in adults. Clinicians cannot rely on scales alone to diagnose ADHD and must undertake more rigorous evaluations of clients who screen positive due to high false-positive rates. Otherwise, clinicians risk inappropriately diagnosing ADHD.

Read “The Ability of Self-Report Methods to Accurately Diagnose Attention Deficit Hyperactivity Disorder: A Systematic Review” Article (PDF 406KB)

Provision of Extended Assessment Time in Post-Secondary Settings

Allyson G. Harrison, Beth Pollock, and Alana Holmes--Psychological Injury and Law, 2022

Although extended time for tests and examinations is the most commonly requested and provided accommodation in postsecondary institutions, best practice guidelines from existing research are rarely translated into practice. This literature review examines support for granting additional assessment time to persons in specific disability categories. 

Read "Provision of Extended Assessment Time in Post‑secondary Settings: a Review of the Literature and Proposed Guidelines for Practice" Article (PDF 214KB)

Archived Research



Academic Accommodations

Memory Aids as a Disability-Related Accommodation? (PDF 130KB)

Allyson G. Harrison, Alana Holmes & Bethany Pollock (2021)


Memory aids are now frequently provided to elementary and secondary school students to increase their success in achieving provincial curriculum standards. While such an accommodation may meet the immediate goal of improved academic performance it may not be warranted based on an actual long-term memory retrieval impairment and may therefore be inequitable, providing an unfair academic advantage relative to non-disabled students. Furthermore, providing memory aid accommodations inappropriately may rob students of the opportunity to learn effective study and retrieval strategies, leading instead to dependence on an accommodation that may not be continued once they enter post-secondary education. An appropriate accommodation at the post-secondary level of education removes a disability-related barrier (functional impairment) and assists only those facing such barriers; under human rights legislation, accommodations are not implemented to guarantee success, reduce anxiety, or provide unequal access to material. Memory aids improve the retrieval of information from long-term storage for everyone. As such, the current widespread provision of this accommodation prior to post-secondary studies must be evaluated critically, with such supports offered only when justified. A six-step process for determining when memory aids are an appropriate accommodation within the post-secondary setting is provided and discussed.

ADHD documentation for students requesting accommodations at the postsecondary level (PDF 153KB)

Allyson G. Harrison & Yontanan Rosenblum (2010)


OBJECTIVE: To update primary health care providers on the guidelines and standards for documentation of attention deficit hyperactivity disorder (ADHD) at the postsecondary level.

QUALITY OF EVIDENCE: We synthesized information from consultations with other experts at postsecondary disability offices and from relevant research in this area (specifically, PsycLIT, PsychINFO, and MEDLINE databases were searched for systematic reviews and meta-analyses from January 1990 to June 2009). Most evidence included was level III.

MAIN MESSAGE: Symptoms of ADHD can occur for many reasons, and primary health care providers need to be cautious when making this diagnosis in young adults. Diagnosis alone is not sufficient to guarantee academic accommodations. Documentation of a disability presented to postsecondary-level service providers must address all aspects of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, criteria for diagnosis of ADHD, and must also clearly demonstrate how recommended academic accommodations were objectively determined.

CONCLUSION: Students with ADHD require comprehensive documentation of their disabilities to obtain accommodations at the postsecondary level. Implementing the guidelines proposed here would improve access to appropriate services and supports for young adults with ADHD, reduce the risk of misdiagnosis of other psychological causes, and minimize the opportunity for students to obtain stimulant medications for illicit use.

De-Implementing Inappropriate Accommodations Practices (PDF 148KB)

Benjamin J. Lovett & Allyson G. Harrison (2021)


Educational accommodations, which alter the manner in which instruction or assessments are administered, are often an appropriate part of a student’s academic program. However, accommodations are frequently overused and have significant limitations. De-implementing inappropriate accommodations is a complex task, but one made easier through a clear understanding of the factors that cause and maintain those accommodations practices. In the present paper, we use the logic of functional behavioral assessment to better understand why evaluators and school staff recommend and provide inappropriate accommodations. We identify problematic background beliefs, specific antecedents, and reinforcing consequences for inappropriate accommodations, before describing several effective strategies for de-implementing those accommodations.

Psychoeducational Assessment Measures

Assessing adult ADHD: New research and perspective (PDF 607KB)

Benjamin J. Lovett and Allyson G. Harrison (2021)

Article Introduction

It is our pleasure to introduce this special issue of the Journal of Clinical and Experimental Neuropsychology on the assessment of adult ADHD. We present a mix of empirical and review articles covering different aspects of the topic, all of them trying to offer useful guidance to practicing neuropsychologists, while also stimulating further research. Assessing ADHD in adults is challenging, requiring skills and techniques that clinicians may not routinely use when assessing other disorders or age groups (Lovett & Davis, 2017). Not all clinicians agree on how to conduct such assessments, and a substantial proportion report a lack of confidence in their ability to reach accurate diagnostic judgments (e.g., Schneider et al., 2019). Furthermore, clinicians who undertake such assessments rarely ensure that all the DSM-5 diagnostic criteria are verified prior to making this diagnosis, at least in young adults (Nelson & Lovett, 2019; Weis et al., 2019).

In this introductory article, we briefly review what the empirical literature has shown about selected issues regarding adult ADHD assessment. We then turn to the highlights of each of the remaining articles in the special issue, discussing how they add to our knowledge base. Finally, we turn to questions raised by the extant literature (including this issue’s articles) that we believe require more attention from researchers.

Comparing Canadian and American Normative Scores on the Wechsler Adult Intelligence Scale-Fourth Edition (PDF 118KB)

Allyson G. Harrison, Irene T. Armstrong, Laura E. Harrison, Rael T. Lange & Grant L. Iverson (2014)

Psychologists practicing in Canada must decide which set of normative data to use for the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV). The purpose of this study was to compare the interpretive effects of applying American versus Canadian normative systems in a sample of 432 Canadian postsecondary-level students who were administered the WAIS-IV as part of an evaluation for a learning disability, attention-deficit hyperactivity disorder, or other mental health problems. Employing the Canadian normative system yielded IQ, Index, and subtest scores that were systematically lower than those obtained using the American norms. Furthermore, the percentage agreement in normative classifications, defined as American and Canadian index scores within five points or within the same classification range, was between 49% and 76%. Substantial differences are present between the American and Canadian WAIS-IV norms. Clinicians should consider carefully the implications regarding which normative system is most appropriate for specific types of evaluations.

What can we learn about performance validity from TOVA response profiles? (PDF 780KB)

Beth Pollock, Allyson G. Harrison & Irene T. Armstrong (2021)


Given the functional impairments associated with Attention Deficit/Hyperactivity Disorder (AD/HD), a valid diagnosis is important. However, particularly when carried out in adulthood, the diagnostic process can be challenging and is complicated by conclusive evidence that a proportion of individuals referred for evaluation of AD/HD exaggerate or feign their symptoms. Relatively few methods, however, exist to identify such feigning. While continuous performance tests (CPTs) may provide useful information regarding performance validity, the question remains as to whether there are consistent patterns of exaggeration demonstrated by those feigning AD/HD. Thus, this study used cluster analysis to determine whether valid and reliable performance clusters would emerge based on CPT performance. Using archival data from a university-based AD/ HD screening clinic, we investigated the performance of 305 adults on the Test of Variables of Attention (TOVA). Three profiles emerged, including one cluster who demonstrated exceptionally low performance on the TOVA, exceptionally high reports of AD/HD symptomology, and higher rates of failure on symptom and performance validity tests. The implication from our analysis is that this group most likely represents individuals who were exaggerating or magnifying their difficulties. The results reaffirm previous research showing that performance profiles on a continuous performance test can be used as an indicator of credible performance.

Neuro- Developmental Disorders

Diagnostic implications of the double deficit model for young adolescents with dyslexia (PDF 209KB)

Allyson G. Harrison & Matthew Stewart (2019)


Considerable support exists for both the phonological core deficit and the naming speed deficit models of dyslexia. The double deficit model proposed that many students with dyslexia might also be impaired in both underlying processes. Employing either performance thresholds (i.e., scores below the 16th or 25th percentile) or k-means clustering as classification methods, the current study investigated whether 154 young adolescents with dyslexia could be categorized into subtypes according to the presence or absence of phonological deficits alone, naming speed deficits alone, or a combination of the two and whether group composition changed depending on classification method. Results support the existence of both single and double deficit groups and confirm that those with both deficits are the most severely impaired across multiple measures. Contrary to previous research, most adolescents were classified as either naming speed only (about a third of the group) or double deficit when defining impairment using performance thresholds to classify groups. This may suggest that although early phonological deficits are amenable to remediation, identification of language symbols fails to become automatized in most individuals with dyslexia and may require more targeted intervention. Classification differences reported in the literature may depend on age and methods employed for classification.

Understanding the biological basis of dyslexia at a neural systems level (PDF 1294KB)

Noor Z. Al Dahhan, John R. Kirby, Donald C. Brien, Rina Gupta, Allyson Harrison & Douglas P. Munoz (2020)


We examined the naming speed performance of 18 typically achieving and 16 dyslexic adults while simultaneously recording eye movements, articulations and fMRI data. Naming speed tasks, which require participants to name a list of letters or objects, have been proposed as a proxy for reading and are thought to recruit similar reading networks in the left hemisphere of the brain as more complex reading tasks. We employed letter and object naming speed tasks, with task manipulations to make the stimuli more or less phonologically and/or visually similar. Compared to typically achieving readers, readers with dyslexia had a poorer behavioural naming speed task performance, longer fixation durations, more regressions and increased activation in areas of the reading network in the left-hemisphere. Whereas increased network activation was positively associated with performance in dyslexics, it was negatively related to performance in typically achieving readers. Readers with dyslexia had greater bilateral activation and recruited additional regions involved with memory, namely the amygdala and hippocampus; in contrast, the typically achieving readers additionally activated the dorsolateral prefrontal cortex. Areas within the reading network were differentially activated by stimulus manipulations to the naming speed tasks. There was less efficient naming speed behavioural performance, longer fixation durations, more regressions and increased neural activity when letter stimuli were both phonologically and visually similar. Discussion focuses on the differences in activation within the reading network, how they are related to behavioural task differences, and how progress in furthering the understanding of the relationship between behavioural performance and brain activity can change the overall trajectories of children with reading difficulties by contributing to both early identification and remediation processes.

Comparison of the neurocognitive profiles of individuals with elevated psychotic or depressive symptoms (PDF 523KB)

Michael Grossman, Michael W. Best, Allyson G. Harrison & Christopher R. Bowie (2017)


Aim: Neurocognitive deficits are pervasive and enduring features of severe mental illness that appear before the onset of clinical symptoms and contribute to functional disability. However, it remains unclear how individuals who display warning signs for psychotic or mood disorders compare on their neurocognitive profiles since previous studies have separately examined neurocognition in both groups. Therefore, the purpose of this study was to directly compare performance on a range of neurocognitive tasks in individuals with emerging psychotic or mood symptoms.

Methods: Participants were drawn from a database of individuals who completed a comprehensive assessment at a university-based assessment centre. We examined 3 groups: individuals who endorsed elevated psychotic symptoms (EPS; n = 64), individuals who endorsed elevated depressive symptoms (EDS; n = 58), or non-clinical comparisons (NCC; n = 57) without any elevated psychiatric symptoms or diagnoses.

Results: EPS participants performed worse than NCC and EDS groups on verbal comprehension, working memory and cognitive flexibility, and worse than NCC, but not EDS, on perceptual reasoning. There were no significant differences between groups on processing speed, verbal fluency and set-shifting. EDS performed worse than both EPS and NCC groups on psychomotor speed. Dimensionally, poorer cognitive functioning was more strongly related to EPS than depressive symptoms.

Conclusions: These findings highlight the distinct yet overlapping neurocognitive profiles of both groups with emerging psychiatric symptoms, and suggest that, despite having no formal diagnosis, individuals with EPS exhibit observable cognitive impairment and may still benefit from interventions within academic and workplace contexts.