Saudi Cultural Missions Theses & Dissertations
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Item Restricted A Cognimetric Authentication Tool (CAT): Temporal Analysis of Touch Dynamics(University of Sussex, 2024) Alwhibi, Munirah; Cheng, PeterMuch research in touch biometric authentication is grounded in a pragmatic, data-driven methodology, involving the collection and analysis of touch data to train machine learning models. In contrast, this research explores the integration of established theories of human cognition and interactive behaviour to inform the design of a Cognimetric Authentication Tool (CAT). In the field of cognitive science, time related measures are widely used to differentiate individuals during task performance. This investigation analyses two temporal measures of swipe and scroll interactions: touch durations (touch) and durations between touches (gap). An existing dataset, comprising interactions from 41 participants engaged in two realistic and cognitively demanding tasks—reading Wikipedia articles (read) and comparing image pairs (compare)—is utilised. The goal of this research is to develop methods for capturing, modelling and comparing participant behaviours for potential authentication applications. It adopts histograms to model and compare temporal behaviours based on the shapes of frequency distributions of each measure within each task. The metric Absolute Distribution Difference (ADD) is introduced by this research to quantify the consistency of temporal behaviour within participants and its distinctiveness across participants. The analysis reveals that intra-participant variations (inconsistency) are overshadowed by inter-participant differences (distinctiveness), which is necessary for authentication. However, the intricate relationship between them emphasises a trade-off; neither is independently sufficient for authentication. Trained only on genuine user’s behaviour, CAT drops error rates to around 10% for a single measure and halving to 5% when combining two measures. To accomplish this, CAT utilises 4 user profiles per participant, tailored to each measure and task, and consisting of the average behaviour of a participant and their personal inconsistency thresholds. This multi-level personalisation approach can compensate for the natural variability and context-dependent nature of human behaviour, and it extends to the fusion functions. Through the research, two sampling techniques are employed: initially, using the entire document as a sample, and subsequently, adopting action-based sampling (a conventional technique). In their current state, both sampling techniques are eligible for delayed authentication, as second factor authentication. Similarly, two fusion methods are employed: measures are combined within the same tasks (a conventional technique), and across tasks, providing complementing aspects of task-specific behaviours. Both sampling and fusion techniques prove effective particularly in relation to the previous research conducted with this dataset.12 0Item Restricted Sex Differences in White Matter Hyperintensities in the Ageing Brain(Saudi Digital Library, 2023-11-22) Alqarni, Abdullah; Wei, Wen; Perminder, Sachdev; Jiyang, JiangCerebral white matter hyperintensities (WMH) appear in the brain magnetic resonance imaging scan at early age and become more prevalent at older age. Despite that old age is known as the main risk factor for WMH accumulation, the literature has shown that many vascular risk factors contribute significantly to the existence and progression of WMH. Women were shown to have higher WMH volume compared to men in the literature. However, the existing literature lacks comprehensive evidence to address why such pattern is noted. Therefore, this thesis aims to examine sex differences in WMH. Specifically, three studies were conducted: (1) investigating sex differences in the associations between vascular risk factors and WMH, (2) examining the contribution of the hormonal risk factors to WMH and their moderation effects on the associations between vascular risk factors and WMH, and (3) examining sex differences in longitudinal associations between vascular risk factors and WMH, and the effects of WMH progression on cognitive decline. Results showed that the pattern of higher WMH in women compared to men was identified across the studies, however, men had stronger contributions of vascular risk factors, especially obesity measures, to WMH. The second study showed that hypertensive postmenopausal women benefited significantly from using hormone replacement therapy, especially when taken early and for longer duration. Diabetic women and women with increased pulse wave velocity had increased deep WMH when post-menopausal duration was one standard deviation below the mean. In men, smokers with higher testosterone levels had significant increase in WMH. In the third study, significant sex differences were found in the association between WMH progression and cognition. Specifically, increases in periventricular WMH volume over time was associated with greater decline in visuospatial abilities in men, but not in women. In women, but not in men, higher average periventricular WMH volumes across time-points was associated with poorer executive function. The thesis comprehensively examined sex differences in vascular and hormonal risk factors associated with WMH, as well as in cognitive consequences of the progression of WMH. The findings highlight the importance of taking sex differences into consideration clinically and for future clinical research of WMH.25 0