Cognitive control provides us with the ability to inter alia, regulate the locus of attention and ignore environmental distractions in accordance with our goals. Auditory distraction is a frequently cited symptom in adults with attention deficit hyperactivity disorder (aADHD)–yet few task-based fMRI studies have explored whether deficits in cognitive control (associated with the disorder) impedes on the ability to suppress/compensate for exogenously evoked cortical responses to noise in this population. In the current study, we explored the effects of auditory distraction as function of working memory (WM) load. Participants completed two tasks: an auditory target detection (ATD) task in which the goal was to actively detect salient oddball tones amidst a stream of standard tones in noise, and a visual n-back task consisting of 0-, 1-, and 2-back WM conditions whilst concurrently ignoring the same tonal signal from the ATD task. Results indicated that our sample of young aADHD (n = 17), compared to typically developed controls (n = 17), had difficulty attenuating auditory cortical responses to the task-irrelevant sound when WM demands were high (2-back). Heightened auditory activity to task-irrelevant sound was associated with both poorer WM performance and symptomatic inattentiveness. In the ATD task, we observed a significant increase in functional communications between auditory and salience networks in aADHD. Because performance outcomes were on par with controls for this task, we suggest that this increased functional connectivity in aADHD was likely an adaptive mechanism for suboptimal listening conditions. Taken together, our results indicate that aADHD are more susceptible to noise interference when they are engaged in a primary task. The ability to cope with auditory distraction appears to be related to the WM demands of the task and thus the capacity to deploy cognitive control.

The large body of research that forms the ease of language understanding (ELU) model emphasizes the important contribution of cognitive processes when listening to speech in adverse conditions; however, speech-in-noise (SIN) processing is yet to be thoroughly tested in populations with cognitive deficits. The purpose of the current study was to contribute to the field in this regard by assessing SIN performance in a sample of adolescents with attention deficit hyperactivity disorder (ADHD) and comparing results with age-matched controls. This population was chosen because core symptoms of ADHD include developmental deficits in cognitive control and working memory capacity and because these top-down processes are thought to reach maturity during adolescence in individuals with typical development. The study utilized natural language sentence materials under experimental conditions that manipulated the dependency on cognitive mechanisms in varying degrees. In addition, participants were tested on cognitive capacity measures of complex working memory-span, selective attention, and lexical access. Primary findings were in support of the ELU-model. Age was shown to significantly covary with SIN performance, and after controlling for age, ADHD participants demonstrated greater difficulty than controls with the experimental manipulations. In addition, overall SIN performance was strongly predicted by individual differences in cognitive capacity. Taken together, the results highlight the general disadvantage persons with deficient cognitive capacity have when attending to speech in typically noisy listening environments. Furthermore, the consistently poorer performance observed in the ADHD group suggests that auditory processing tasks designed to tax attention and working memory capacity may prove to be beneficial clinical instruments when diagnosing ADHD.

Predictions Influence Cortical Speech Processing-Preference for phonological information is observed in the left auditory cortex during sentence processing.-Unrelated speech elicits larger N400 amplitudes than partially related speech (at semantic or phonological level) under adverse listening conditions.-N400 effects appear to be more associated with the strength of deviation rather than the type of deviations.-Working Memory plays a critical role in rejecting deviant stimuli and integrating expected ones.

ADHD is a heterogenous disorder encompassing neurodevelopmental deficits in cognitive control. Auditory distraction is a common clinically reported symptom in ADHD, yet empirical research investigating the manifestation of auditory distraction in the disorder is remarkably scarce. Findings from cognitive hearing science highlight the crucial role cognitive control plays in an individual's ability to gate, attenuate and/or compensate for auditory distraction. However the field is yet to extensively test hypotheses in normal hearing populations with neurodevelopmental deficits in cognitive control such as ADHD. This thesis contributes to narrowing the gap within these two fields of research by studying auditory distraction in this clinical population to a greater extent than previous reports in the literature.Using a combination of both behavioural and neuroimaging methods, the research presented here was able to show that adults and adolescents with ADHD are inherently more susceptible to auditory distraction than their non-ADHD counterparts. At the behavioural level, impaired task performance due to auditory distraction was more likely to manifest in ADHD participants when the working memory system was under high processing load. At the neural level, functional aberrancy in auditory attention was evident at early stages of sensory processing in a variety of tasks, implicating both exogenous and endogenous control systems in ADHD. Furthermore, the distribution of ADHD-symptom severity across participants was shown to correlate with increases in both cortical activity to auditory distractors and intrinsic functional connectivity between auditory and exogenous attention networks.In line with evidence from cognitive hearing science, the general findings of this thesis demonstrate that cognitive control plays an important role in the ability to perceive sound under suboptimal listening conditions and hamper distraction. In addition, findings challenge theories of ADHD that question the extent in which sensory-related attentional control is impaired. More empirical research on the auditory modality in ADHD is therefore encouraged in order to revise models, improve diagnostic tools, and develop evidence-based interventions targeting study/work environments. STUDIES Empirical StudiesThe current thesis is based on the following four empirical studies and ensuing reference to these studies will use their assigned Roman numerals. Studies I and II are published in open-access peer reviewed journals.

BackgroundNumerous resting-state studies on attention deficit hyperactivity disorder (ADHD) have reported aberrant functional connectivity (FC) between the default-mode network (DMN) and the ventral attention/salience network (VA/SN). This finding has commonly been interpreted as an index of poorer DMN regulation associated with symptoms of mind wandering in ADHD literature. However, a competing perspective suggests that dysfunctional organization of the DMN and VA/SN may additionally index increased sensitivity to the external environment. The goal of the current study was to test this latter perspective in relation to auditory distraction by investigating whether ADHD-adults exhibit aberrant FC between DMN, VA/SN, and auditory networks.MethodsTwelve minutes of resting-state fMRI data was collected from two adult groups: ADHD (n = 17) and controls (n = 17); from which the FC between predefined regions comprising the DMN, VA/SN, and auditory networks were analyzed.ResultsA weaker anticorrelation between the VA/SN and DMN was observed in ADHD. DMN and VA/SN hubs also exhibited aberrant FC with the auditory network in ADHD. Additionally, participants who displayed a stronger anticorrelation between the VA/SN and auditory network at rest, also performed better on a cognitively demanding behavioral task that involved ignoring a distracting auditory stimulus.ConclusionResults are consistent with the hypothesis that auditory distraction in ADHD is linked to aberrant interactions between DMN, VA/SN, and auditory systems. Our findings support models that implicate dysfunctional organization of the DMN and VA/SN in the disorder and encourage more research into sensory interactions with these major networks.