Melbourne School of Psychological Sciences - Theses
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ItemThe relationships between response time variability, brain signals, ADHD symptoms, and behavioural control( 2018)Individuals with Attention Deficit Hyperactivity Disorder (ADHD) often produce greater response time variability (RTV) when performing cognitive tasks. It is still unclear why increased RTV is observed in ADHD. One possible explanation for this is that individuals with ADHD may have aberrant patterns of brain connectivity, leading to inefficient communication between brain regions. Graph theoretical analysis is an approach used to characterise patterns of brain connectivity. This study aimed to investigate the relationship between brain connectivity, RTV, age, and levels of ADHD symptoms using a cross sectional design. Children aged 9-12 years and adolescents aged 15-18 years performed three tasks in this thesis - the Sustained Attention to Response Task (SART), the Flanker SART, and the Detection of Disappearance Task (DDT). EEG was recorded while participants performed the three tasks. The Conners 3 questionnaire was used to measure the participants' levels of ADHD symptoms. Multiple parameters were computed to reflect different aspects of RTV, using ex-Gaussian and the Fast Fourier Transform (FFT) techniques. Tau from the ex-Gaussian analysis reflects skewness and sigma reflects deviation of the Gaussian portion of the RT distribution. The FFT analysis allows an examination of periodic changes in RT, with moment-to-moment variability (Fast Frequency Area Under the Spectra, FFAUS) and slow changes in RT (Slow Frequency Area Under the Spectra, SFAUS) computed. The ex-Gaussian analysis was performed in all three studies, and the FFT analysis was performed in the SART and Flanker SART. From the EEG recording, functional connectivity between 64 electrodes was examined, and global efficiency and modularity were computed, reflecting functional integration and segregation of the brain respectively. There was a positive association between tau and levels of ADHD symptoms in all three studies, but sigma showed no significant association in any of the studies. This finding suggests that higher levels of ADHD symptoms are associated more occurrences of attentional lapses and greater RTV. FFAUS was positively associated with levels of ADHD symptoms in both the SART and Flanker SART, suggesting that individuals with higher levels of ADHD symptoms show difficulty with sustained attention. SFAUS was positively associated with levels of ADHD symptoms only in the SART. Greater task complexity presented by flankers might help to increase arousal levels for those with more pronounced levels of ADHD symptoms. Adolescents demonstrated lower RTV than the children in all RTV measures, indicating stability of performance increases from late childhood to late adolescence. The graph analysis of EEG functional connectivity showed that lower RTV was associated with more integrated brain network functioning, as measured by global efficiency. This supports the view that stable responses are achieved through more integrated brain functioning. More integrated brains may allow for more efficient transfer of information resulting in more stable responses. Adolescents showed greater levels of integration and lower levels of segregation of the brain during performance, suggesting that the brain might be becoming more integrated and less segregated from late childhood to late adolescence.
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ItemA longitudinal study of attention and inhibitory control in 6- to 11-year-old children( 2017)Attention and inhibitory control are important cognitive abilities. Attention consists of three components: activation, selection, and control. The activation of attention involves alertness, the maintenance of response readiness, and sustained attention. The selection of attention involves reflexive and voluntary shifts of attention to a specific location or point in time, and the breaking and reorienting of attention. The control of attention involves resolution of conflict, such as that induced by distractors, and inhibitory control. There is a lack of longitudinal data on the development of these aspects of attention in typically developing children, so their developmental trajectories remain unclear. The aim of this thesis was to map the developmental trajectories of alerting, sustained attention, orienting, reorienting, conflict resolution and inhibitory control. Participants involved in this research were 114 children aged 6, 8, or 10 years at study onset, referred to as the 6-7, 8-9, and 10-11 groups. Children performed three attention tasks, three times at 6-monthly intervals. The Attention Network Task (ANT) measures alerting, orienting, reorienting, and conflict resolution. The Random Sustained Attention to Response Task (SART) and the Fixed SART measure sustained attention and response inhibition; they require frequent responding with infrequent inhibition to a No-Go target. Intra-individual variability of response time (RT) during the SART was analysed with a Fast Fourier Transform and an ex-Gaussian model of RT data. Results indicate that each component of attention followed a different rate of development. In terms of activation, there was ongoing maturation throughout the study. The functioning of the alerting network, as measured by the ANT, improved over the year in all children. There was, however, little difference in alerting score between the two youngest groups, suggesting greater maturation of alerting after 9 years of age than before. Findings for sustained attention were task-dependent: during the arousing Random SART, there were few differences in performance between the two older groups, but during the unengaging Fixed SART, the 8-9 group mostly performed at an intermediate level compared with the other groups. The 8-9 group exhibited greater momentary fluctuations in response time and made more very long responses than the 10-11 group on both SARTs, indicating more momentary lapses in attention. The 6-7 group performed less well than the older groups on most measures on both SARTs. The selection of attention - the orienting and reorienting networks as measured by the ANT - showed no developmental changes during the study. Control of attention - conflict resolution and response inhibition as measured by the ANT and Random SART - was relatively stable from 7 and 8 years respectively. This thesis proposes that between 6 and 7 years is an important period for the development of attention and response inhibition. There may be some level of developmental stability between 8 and 11 years on unpredictable engaging tasks. The ability to self-sustain attention and arousal on an unarousing unengaging task, however, appears to follow a protracted maturation throughout childhood.