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  • The perceptual experience of body ownership in Virtual Reality (VR)
    (2024) Haghzare, Leyla
    Thesis
    Virtual reality (VR) has redefined and extended human experiences, offering immersive environments that simulate real-life scenarios through human-computer interaction and remote human-to-human social engagement. This study investigates the complex multisensory interactions that underlie the relationship between the experience of presence, agency, and perceived body ownership in VR. Utilizing a head-mounted display (HMD), this research examines how the alignment of visual and proprioceptive cues (visual- proprioceptive offset and vibrational somatosensory feedback) influences hand-eye coordination, and sense of presence, agency, and body ownership in VR. The study consisted of two VR experiments examining the effect of multisensory integration and visual-proprioceptive offset on these perceptual constructs. The initial experiment explored the effect of multisensory integration on human perception and performance. We adjusted visual, tactile and auditory stimuli levels and imposed systematic variations in virtual hand offset relative to the user’s real hands. This offset involved an artificially imposed medial/lateral spatial displacement between the virtual representation of the hand relative to the physical location of their hand in the real world. In a series of 90-s training tasks, participants used virtual mallets to strike virtual orbs in a hand-eye coordination game. Presence or absence of vibrational feedback and simulated virtual hands holding the mallets were also systematically varied. Significant effects of visual hand offset, vibration and virtual hand presentation were found but differentially affected perceptual accuracy, perceived body ownership, agency, and strike task performance. Positive linear inter-correlations were found between presence, perceived body ownership, and agency, emphasizing their interdependent nature. In the Experiment 2, we assessed extinction of the associative learning between vision and proprioception during training with hand offset via repetitive hand strikes to a target. The subsequent study illustrated how repetition influences the extinction process. Furthermore, when comparing the positional precision of striking performance in the Experiment 1 and Experiment 2, it became evident that time plays a significant role in strike performance. These results strongly support multisensory integration's role in associative learning and HMD VR’s capability for use as a training platform for altering sensorimotor weighting. This study advances our understanding of virtual body ownership in VR, which has potential applications across diverse areas of social benefit. Implications for fields like medicine, education and rehabilitation are discussed, emphasising the importance of presence and multisensory integration in contributing to behavioural outcomes achieved through engagement in HMD VR training activities.
  • Exploring clinical phenotypes of open-angle glaucoma and their significance in practice
    (2023) Rafla, Daniel
    Thesis
    There are several enduring questions regarding the differentiation of clinical phenotypes of glaucoma which clinicians may derive clinical meaning directed towards patient’s management and prognostication. This thesis seeks to address the following issues relating to distinguishing clinical phenotypes of glaucoma: “Evaluating the impact of changing visual field test density on macular structure-function relationships to identify central-involving glaucoma phenotypes”; and “Identifying quantitative structural and functional clinical parameters that may distinguish between intraocular pressure (IOP) defined glaucoma phenotypes”; Two studies were undertaken to examine clinical phenotypes of glaucoma. The first study utilised systematic approach to assessing the impact of test point density in macular visual field (VF) testing on structure-function concordance for identifying centrally-involving glaucoma phenotypes. The second study used multivariate regression analysis and principal component analysis (PCA) to examine quantitative structural (using optical coherence tomography) and functional (VF) clinical data of newly-diagnosed glucoma patients to determine if there are clinically meaningful distinctions between IOP-defined phenotypes (i.e. low-tension vs high-tension glaucoma). Study 1) Using a systematic approach of test point addition and subtraction, we identified a critical number of test locations (8-14) in macular VF testing where binarised structure-function concordance is maximised, and discordance minimised. This methodology provides a framework for optimising macular VF test patterns for detection of centrally-involving glaucoma phenotypes. Study 2) Despite statistical significance in differences between low- and high-tension glaucoma, PCA applied to quantitative clinical structural and functional parameters returned no groups of clinical parameters that reliably distinguished between patients in IOP-defined glaucoma phenotypes. The present work provides a framework to identify phenotypic groups of glaucoma, the clinical significance of which may vary. We identified the minimum number of test points required to detect central-involving glaucoma in visual field testing. We also demonstrate that IOP-defined phenotypes are not clinically distinguishable at the point of diagnosis, suggesting that these phenotypes form part of a continuum of open-angle glaucoma. These findings have implications for disease staging and preferred treatment modality.