Kazazi, Fjorda; (2023) Assessing Executive Function Impairments and Comorbidity between ADHD and Stuttering. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Stuttering and ADHD are often considered ‘comorbid’ because different types of symptoms and processing issues occur in, for example, fluency, attention and working memory. This thesis addresses whether or not these shared factors signify fundamental similarities between stuttering and ADHD that distinguish them from typical controls. This is done in two main ways: First, a comparison is made of details of performance on attention capabilities using a range of behavioural and physiological measures in various test environments, including Web and VR approaches; Second, modelling analyses are conducted that compare networks representing participants’ performance across groups. Using the Load Theory of Attention methodology (Chapter 2), which addresses how to focus attention and ignore distractions up to a point where load exceeds perceptual capacity, it was observed that the performance of participants who stutter was significantly lower from the performance of controls in the auditory selective and divided attention tasks. The results showed that tasks in which attention demands enhanced were effective in detecting limitations in audio processing by PWS. Extending the task in the visual, audio and audio-visual domains in a virtual reality environment in people who stutter, (PWS) as well as people with ADHD (PWADHD) it was found that while audio was more affected in PWS, audio and audio-visual domains were affected in PWADHD. Lastly, Network Models (NMs) from the measures examined showed that comorbidity between PWS and PWADHD is limited. For better clinical assessments of attention, fluency and working memory problems, a Linear Mixed Model (LMM) was included in chapter 3 to understand if gender imbalance affected the results of PWS, PWADHD and controls in a selective attention task. LMM correctly determined that the gender imbalance did not affect the participants performance and PWS performed significantly worse from PWADHD showing that the groups were not comorbid and PWS is impaired in selective attention tasks. Further investigations were made in chapter 4 on PWS, PWADHD and controls in which data collected was extended to behavioural as well as physiological measures in a selective attention task implemented in a Virtual Reality (VR) environment. Although both PWS and PWADHD differed from controls with lower performance on the task, impulsive behaviours were only present in PWADHD (higher NOF) while inattentiveness was observed only in PWS (lower FD, higher theta activity). The architecture of NMs was different between PWS and PWADHD in task performance confirming again that comorbidity between groups is overstated while the frontal cortex is impaired in both groups as shown by NMs from EEG measures. While previous chapters showed that selective and divided attention tasks in Executive Function (EF) can correctly assess attention problems in PWS, chapters 5, 6 and 7 aimed at understanding which attention type in EF is impaired in PWADHD and can correctly assess attention problems in this group. An extensive investigation was made from 10 VR tasks that drew upon different attention types on behavioural measures and responses from questionnaires (chapter 5), eye measures (chapter 6) and brain activity (chapter 7). PWADHD were compared to controls on all the measures. NMs showed that sustained attention tasks in all domains and switched attention task only in the visual domain assessed ADHD traits in PWADHD on the measures examined. Furthermore, prefrontal cortex was impaired as shown from NMs in EEG measures. Finally, NMs were compared between controls, PWADHD and PWS in chapter 8 on cognitive factors including attention, fluency and working memory. NMs confirmed previous findings that the comorbidity of symptoms of both disorders is overstated. NM architecture between controls and PWADHD was similar, but both differed from PWS. Working memory was a strong factor that affected attention in all groups but the way it affected attention differed between PWS and PWADHD.

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