Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy




Joanisse, Marc F.


High rates of comorbidity in attention-deficit/hyperactivity disorder (ADHD) and developmental language disorder (DLD) have motivated interest in utilizing psycholinguistic and physiological metrics to distinguish between these conditions. However, past studies have focused on one disorder and overlooked the significant overlap in symptoms between ADHD and DLD. Consequently, less is known about how these assessments can distinguish between “pure” (no comorbidities) cases of either disorder or comorbidities. This thesis aims to elucidate the basis of these overlapping disorders by examining language, reading, and resting-state oscillatory power differences and assessing their potential in distinguishing ADHD and/or DLD. Chapter 2 presents a scoping review of research on language abilities in ADHD and DLD. It revealed that children with ADHD had better morphosyntax/grammar, general/core language, receptive, and expressive language than those with DLD. However, there were variations in assessments of phonological processing, syntax, narrative language, and vocabulary. On the other hand, performance on semantic, pragmatics, and figurative language assessments were similar between groups. Standardization across studies is highlighted as crucial to consolidate inconsistencies and gain a clear understanding of the distinct language difficulties associated with each disorder. Chapter 3 builds on the findings of Chapter 2 by investigating whether the presence of a comorbid language disorder exacerbates language and reading difficulties in ADHD. Additionally, this chapter explores the ability of psycholinguistic assessments to distinguish between groups: ADHD (combined or inattentive subtype), DLD, and comorbid ADHD + DLD. Measures of reading efficiency could distinguish between the two types of ADHD, but not between other groups. Interestingly, scores on the standard language screener were no worse for children with ADHD + DLD than children with DLD only. These findings offer valuable insights into differential diagnosis and the identification of comorbidity In Chapter 4, resting-state electroencephalography (EEG) was used to examine oscillatory power differences in ADHD, comorbid ADHD + DLD, and control groups. It also examined whether groups could be distinguished based on their oscillatory power patterns. While EEG power spectra differences were observed between pure and comorbid ADHD + DLD, resting-state EEG was unable to accurately distinguish any of the groups with high accuracy, suggesting limited reliability as a diagnostic tool. Chapter 5 summarizes the findings of this thesis in relation to the shared cognitive deficits in ADHD and DLD and pathways contributing to comorbidity.

Summary for Lay Audience

Distinguishing between attention-deficit/hyperactivity disorder (ADHD) and developmental language disorder (DLD) can be challenging due to their frequent co-occurrence and the overlap in their symptoms. Previous studies have explored language and physiological measures to distinguish these disorders but often neglect the significant symptom overlap. This thesis aims to shed light on the shared characteristics of these disorders and evaluate the potential of psycholinguistic assessments and resting-state electroencephalography (EEG) in distinguishing children with ADHD, DLD, and co-occurring ADHD + DLD.

The first study provides an overview of research on language abilities in ADHD and DLD. Children with ADHD exhibited better language skills than those with DLD, particularly in areas such as grammar, general language, receptive language, and expressive language. However, the findings varied across studies, and semantic and figurative language performance was similar between the two groups. Standardization across studies is emphasized to achieve a clearer understanding of the distinct language difficulties associated with ADHD and DLD.

The next two studies of this thesis expanded on the findings from the first study by comparing the different language, reading, and resting-state brain activity patterns of children and adolescents with ADHD, DLD, and co-occurring ADHD + DLD. These studies also investigate whether performance on language and reading assessments and resting-state brain activity can distinguish between these groups. The results showed that standard language and reading measures can help distinguish between ADHD and DLD, and different subtypes of ADHD. Further, that children and adolescents with co-occurring ADHD + DLD exhibit distinct resting-state brain patterns compared to those with ADHD-only.

Overall, the findings of this thesis demonstrate that there are similarities and differences in the language, reading, and resting-state brain patterns between children with ADHD and those with co-occurring ADHD + DLD, which can aid in distinguishing between the two groups. These findings contribute to our understanding of the behavioural and biological factors underlying ADHD, DLD and their co-occurrence.