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  • (2022) Han, Nathan Thomas
    Thesis
    Stimuli generated by a person’s own willed actions generally elicit a suppressed neurophysiological response than physically identical stimuli that have been externally generated. This phenomenon, known as sensory attenuation, has primarily been studied by comparing the N1, Tb and P2 components of the event-related potentials (ERPs) evoked by self-initiated vs. externally generated sounds. Sensory attenuation has been implicated in some psychotic disorders such as schizophrenia, where symptoms such as auditory hallucinations and delusions of control have been conceptualised as reflecting a difficulty in distinguishing between internally and externally generated stimuli. This thesis employed a novel paradigm across five experiments to investigate the role of agency and contingency in sensory attenuation. The role of agency was investigated in in Chapter 2. In Experiment 1, participants watched a moving, marked tickertape while EEG was recorded. In the active condition, participants chose whether to press a button by a certain mark on the tickertape. If a button-press had not occurred by the mark, then a tone would be played one second later. If the button was pressed prior to the mark, the tone was not played. In the passive condition, participants passively watched the animation, and were informed about whether a tone would be played on each trial. The design for Experiment 2 was identical, except that the contingencies were reversed (i.e., pressing the button prior to the mark led to a tone). The results were consistent across the two experiments: while there were no differences in N1 amplitude between the active and passive conditions, the amplitude of the Tb component was suppressed in the active condition. The amplitude of the P2 component was enhanced in the active condition in both Experiments 1 and 2. These results suggest that agency and motor actions per se have differential effects on sensory attenuation to sounds and are indexed with different ERP components. In Chapter 3, we investigated the role of contingency in sensory attenuation while using a similar ticker-tape design in Chapter 2. In the Full Contingency (FC) condition, participants again chose whether to press a button by a certain mark on the tickertape. If a button-press had not occurred by the mark, a sound would be played (one second later) 100% of the time (Experiment 3). If the button was pressed prior to the mark, the sound was not played. In the Half Contingency (HC) condition, participants observed the same tickertape; however, if participants did not press the button by the mark, a sound would occur 50% of the time (HC-Inaction) while if the participant did press the button, a sound would also play 50% of the time (HC-Action). In Experiment 4, the design was identical, except that a button-press triggered the sound in the FC condition. The results were consistent across both Experiments in Chapter 3: while there were no differences in N1 amplitude across the FC and HC conditions, the amplitude of the Tb component was smaller in the FC condition when compared to the HC-Inaction condition. The amplitude of the P2 component was also smaller in the FC condition compared to both the HC-Action and HC-Inaction conditions. The results suggest that the effect of contingency on neurophysiological indices of sensory attenuation may be indexed by the Tb and P2 components, as opposed to the more heavily studied N1 component. Chapter 4 also investigated contingency but instead used a more ‘traditional’ self-stimulation paradigm, in which sounds immediately followed the button-press. In Chapter 4, participants observed a fixation cross while pressing a button to generate a sound. The probability of the sound occurring after the button-press was either 100% (active 100) or 50% (active 50). In the two passive conditions (passive 100 and passive 50), sounds generated in the corresponding active conditions were recorded and played back to participants while they passively listened. In contrast with the results of Chapter 3, the results of Chapter 4 showed both the classical N1 suppression effect, and also an effect of contingency of the N1, where sounds with a 50% probability generated higher N1 amplitudes compared to sounds with 100% probability. In contrast, Tb amplitude was modulated by contingency but did not show any differences between the active and passive conditions. The results of this study suggest that both sense of agency and sensory contingency can influence sensory attenuation, and thus should be considered in future studies investigating this theoretically and clinically important phenomenon.

  • (2022) Peterson, Lindsay
    Thesis
    The light sources in a scene can drastically affect the pattern of intensities falling on the retina. However, it is unclear how the visual system represents the light sources in a scene. One possibility is that a light source is treated as a scene component: an entity that exists within a scene and interacts with other scene components (object shape and object reflectance) to produce the retinal image. The aim of this thesis was to test two key predictions arising from a perceptual framework in which light sources and the objects they illuminate are considered to be scene components by the visual system. We begin examining the first prediction in Chapter 3, focusing on the role of a dynamic shape cue in the interaction between shape, reflectance, and lighting. In two psychophysics experiments, we show that the visual system can "explain away'" alternative interpretations of luminance gradients using the information provided by a dynamic shape cue (kinetic depth). In subsequent chapters, the research focus shifts to the second prediction, investigating whether multiple objects in a scene are integrated to estimate light source direction. In Chapter 4, participants were presented with scenes that contained 1, 9, and 25 objects and asked to judge whether the scenes were illuminated from the left or right, relative to their viewpoint. We found that increasing the number of objects in a scene worsened, if anything, discrimination sensitivity. To further understand this result, we conducted an equivalent noise experiment in Chapter 5 to examine the contributions of internal noise and integration to estimates of light source direction. Our results indicate that participants used only 1 or 2 objects to judge light source direction for scenes with 9 and 25 objects. Chapter 6 presents a shape discrimination experiment that required participants to make an implicit, rather than explicit, judgement of light source direction. Consistent with the results reported in Chapters 4 and 5, we find that shape discrimination sensitivity was comparable for scenes containing 1, 9, and 25 objects. Taken together, the findings presented here suggest that while object shape and reflectance may be represented as scene components, lighting seems to be associated with individual objects rather than having a scene-level representation.

  • (2022) Wong, Francesca
    Thesis
    This thesis used a three-stage sensory preconditioning protocol to investigate how the perirhinal cortex (PRh) and basolateral amygdala complex (BLA) integrate different types of associations. In stage 1, rats were exposed to pairings of two innocuous stimuli, S2 and S1. In stage 2, they were exposed to pairings of the S1 and foot shock. Finally, in stage 3, test presentations of either stimulus elicited defensive responses indicative of fear in people (such as freezing) even though the S2 was never paired with danger. Previous studies showed that the S2-S1 association formed in stage 1 requires neuronal activity in the PRh but not the BLA; whereas the S1-shock association formed in stage 2 requires neuronal activity in the BLA but not the PRh. A pharmacological approach was used to examine: 1) when the S2-S1 association is integrated with the S1-shock association to generate sensory preconditioned fear of S2; and 2) how the PRh and BLA communicate to achieve this integration. The first series of experiments shows that sensory preconditioned fear of S2 involves "online" integration of the S2-S1 and S1-shock associations in stage 2 of training rather than at the time of testing in stage 3. Specifically, it shows that silencing neuronal activity in the PRh before or after the session of S1-shock pairings spares fear conditioning of this stimulus but disrupts the expression of sensory preconditioned fear to S2 at test. These findings were taken to mean that the PRh retrieves information about the S2 when rats are exposed to S1-shock pairings, resulting in formation of a mediated S2-shock association; and that, once formed, this mediated association is consolidated in the PRh. The second series of experiments shows that cooperation between the PRh and BLA is needed to establish the mediated S2-shock association in stage 2, but is not needed for its retrieval/expression at the time of testing; and, that at the level of NMDA receptor activation, the involvement of the PRh and BLA in acquiring fear to S2 remains distinct. These findings are discussed with respect to the broader roles of the PRh and BLA in associative formation: specifically, the determinants of their roles in learning and memory and how they communicate with wider systems/circuits to achieve learning and memory.

  • (2022) Sloane, Jennifer
    Thesis
    From a child interrupting a conversation between her parents to ask "What's for dinner?" to a nurse interrupting a physician in the middle of a complex procedure with an urgent message, interruptions are an inevitable part of our daily lives no matter who we are, where we live, or what we do. Interruptions can have a variety of affects on people's performance and behavior. While interruptions may sometimes facilitate performance, often interruptions have negative consequences. For example, interruptions may result in people making more errors or forgetting to complete a prior task altogether. This thesis examines existing strategies to help mitigate interruption costs and explores the effects of interruptions within different decision environments. Chapter I introduces the topic by discussing a few theoretical frameworks of interruptions and reviewing prior research on what makes interruptions disruptive. One strategy to minimize interruption costs is to use what is called an interruption lag, which can be thought of as taking time to prepare for a pending interruption. Chapter II presents a novel experiment to systematically explore the potential benefits of interruptions lags and an alternative intervention (i.e. providing feedback) when interruption lags are not possible. Chapters III and IV discuss the results from three experiments and a final replication study that all focus on how interruptions affect people's decision making in unique environments. The environments consist of easy problems (i.e. basic arithmetic problems) and trick problems, designed in such a way to lead the reader down an incorrect path. Results from these studies were mixed. While there was some evidence that interruptions may make people more susceptible to falling for the trick answer, this finding was inconsistent across all the experiments. Chapter V applies the findings from the previous chapters to a medical context. This chapter presents novel medical cases that were developed with the help of a medical expert. These cases consisted of easy, hard, and trick cases designed for medical students. The goals of this chapter were to validate the cases and to investigate the effects of interruptions within the different case types. The final chapter (Chapter VI) concludes with a general discussion of the experimental findings, the theoretical implications of the results, and the broader implications of this research for the field of medicine.

  • (2022) Jamshidi, Javad
    Thesis
    Wellbeing, a key aspect of mental health, is defined as a state of positive subjective experience and optimal psychological functioning. This thesis presents a series of studies devised to comprehensively explore phenotypic, genetic, and neural correlates of wellbeing. The first study (Chapter 2) aimed to compare the heritability and stability of different wellbeing measures in the TWIN-E dataset (N~1600) to discern the most suitable approach for measuring wellbeing for subsequent gene discovery efforts. This twin-based study concluded that multi-item measures of wellbeing such as the COMPAS-W scale, were more heritable and stable than single-item measures. Wellbeing-associated variants were identified via genome-wide association studies (GWAS) and highlighted the need for larger sample size. The subsequent studies were conducted using population-scale data from the UK Biobank comprising ~130,000 participants with phenotypic and genetic data. Thus, in Chapter 3, I constructed a multi-item “wellbeing index” measure using UK Biobank data to investigate its relationship phenotypically and genetically (using GWAS, polygenic scores and LD score regression) with negative mental health indicators (e.g., neuroticism and loneliness), childhood maltreatment and psychiatric illness. I confirmed that SNP-heritability of wellbeing index was higher than both single-item measures and estimates previously reported (SNP-h2 = 8.6%). Moreover, I provide an overview of phenotypic and genetic correlations between wellbeing index and negative mental health indicators. In addition, childhood maltreatment and psychiatric illnesses were associated with reduced wellbeing, with evidence that genetic factors may influence their correlations. In Chapter 4, I investigated the genetic and phenotypic associations between wellbeing index and brain structure, using magnetic resonance image-derived phenotypes from the UK Biobank. This study found associations between wellbeing and volumes of brainstem, cerebellum and subcortical regions, and structural morphology of various cortical regions. Thus, wellbeing is associated with complex structural variations, each with a small effect. Together, this thesis explores the multifaceted nature of wellbeing, elucidating its phenotypic and genetic relationships with related phenotypes, childhood maltreatment, and psychiatric outcomes, and provides novel insights into the associations between wellbeing, its genetic signatures and brain structure.

  • (2022) Liang, Garston
    Thesis
    Algorithms are increasingly present in everyday life. These tools have moved beyond their traditional online habitats to analysing data about how people choose to commute or browse a dinner menu. This thesis investigated when and why people use algorithms as decision aids to guide their choices. I examined this central question in three experimental designs that spanned from applied investigations with radiologists to studies in the laboratory and then returning to examining algorithm-based scenarios in the real-world. Across 14 experiments, our results highlight the central role of the individual’s knowledge about the algorithm. In various formats, we provided individuals with algorithm performance information that allowed them to compare their own abilities (or the abilities of others) to an algorithm. We show that once equipped with this information, individuals adopt a strategy of selective reliance on the decision aid. That is, individuals ignore the algorithm when their abilities surpass the algorithm and appropriately defer to it when faced with choices under uncertainty. Our systematic investigations show that further opportunities to learn about the algorithm not only encourage reliance on its recommendations but also engagement in experimentation and verification of one’s knowledge about its capabilities. Together, our findings emphasise the decision-maker’s capacity to learn about the algorithm to provide insights for how we can improve the use of decision aids.

  • (2022) Montalto, Arthur
    Thesis
    Good mental health is not only related to the absence of psychopathology, but also to optimal mental wellbeing. Although greater wellbeing and resilience have been associated with higher levels of cognitive performance, little is known about the relationship between the neural circuits engaged during cognitive processes and wellbeing and resilience, and whether genetics or the environment contribute to these associations. Thus, the aim of this thesis is to explore the relationships between wellbeing, resilience to trauma and the neural correlates of cognitive functions using functional Magnetic Resonance Imaging (fMRI) and to understand how different genetic and environmental factors may modulate these relationships using a sample of healthy adult twins. After an introduction on the key concepts of this thesis, Chapter 2 explores the relationship between wellbeing, resilience and functional activation during tasks probing processes of sustained attention, working memory, inhibition and selective attention. It reveals a negative association between bilateral anterior insula (aI) activation during a sustained attention task and wellbeing in an early trauma-exposed sub-sample, indicating resilience. Chapter 3 explores functional connectivity between these regions and how it relates to levels of wellbeing and resilience. This chapter shows a negative relationship between resilience and the precentral gyri (PCG) connectivity during a selective attention task. Chapter 4 examines how much genetics contribute to functional activation and connectivity probed by cognitive tasks. Univariate twin modelling shows low heritability of aI activation and PCG connectivity. Multivariate analyses show that the association between wellbeing and aI activation in the trauma-exposed sample was mostly driven by common genetic factors, while no significant genetic or environmental correlations between PCG connectivity and wellbeing were found. Finally, in Chapter 5, I discuss the findings, implications and limitations of this thesis. Overall, this thesis shows relationships between neural correlates of attention and wellbeing in an early trauma-exposed sample (indicating resilience), and potential shared genetic factors underlying aI activation and resilience. This provides evidence for the use of fMRI correlates of cognitive functions as biomarkers of resilience and opens new avenues for future research seeking to understand wellbeing and resilience in the general population.

  • (2022) Cao, Jun
    Thesis
    This thesis focuses on the development and applications of magnetic resonance electrical properties tomography (MREPT), which is an emerging imaging modality to noninvasively obtain the electrical properties of tissues, such as conductivity and permittivity. Chapter 2 describes the general information about human research ethics, MRI scanner, MR sequence and the method of phase-based MREPT implemented in this thesis. Chapter 3 examines the repeatability of phase-based MREPT in the brain conductivity measurement using balanced fast field echo (bFFE) and turbo spin echo (TSE) sequences, and investigate the effects of compressed SENSE, whole-head B_1 shimming and video watching during scan on the measurement precision. Chapter 4 investigates the conductivity signal in response to short-duration visual stimulus, compares the signal and functional activation pathway with that of BOLD, and tests the consistency of functional conductivity imaging (funCI) with visual stimulation across participants. Chapter 5 extends the use of functional conductivity imaging to somatosensory stimulation and trigeminal nerve stimulation to evaluate the consistency of functional conductivity activation across different types of stimuli. In addition, visual adaptation experiment is performed to test if the repetition suppression effect can be observed using funCI. Chapter 6 explores if resting state conductivity networks can be reliably constructed using resting state funCI, evaluates the consistency of persistent homology architectures, and compares the links between nodes in the whole brain. Chapter 7 investigates the feasibility of prostate conductivity imaging using MREPT, and distinctive features in the conductivity distribution between healthy participants and participants with suspected abnormalities.

  • (2022) Shvetcov, Artur
    Thesis
    Rodents learn to fear a stimulus (e.g., a light) that signals the imminent arrival of an innate source of danger (typically an aversive foot shock). They also learn to fear a stimulus (e.g., a noise) that signals a learned source of danger (e.g., the already conditioned fear-eliciting light). Following Pavlov (1927), the former type of fear is termed first-order conditioned fear, because the stimulus is paired with an aversive unconditioned stimulus (US). The latter is termed second-order conditioned fear, because the stimulus is paired, not with a US, but with an already conditioned stimulus. There are both commonalities and differences in the neural substrates underlying these two forms of fear. Both require neuronal activity in the basolateral amygdala complex (BLA), including activation of NMDA receptors, for their encoding, and both require CaMK signalling, gene expression and DNA methylation for their consolidation. However, de novo protein synthesis is required for consolidation of first-order fear but not for consolidation of second-order fear.

  • (2022) Trinh, Anita
    Thesis
    Faces that are encountered on a day-to-day basis and in applied identity verification tasks. Faces are often accompanied with some form of contextual information, such as biographical details in the case of applied tasks or environments in everyday life. While many studies have examined how our decision, memory or recognition associated with faces can be influenced by the presence of such contextual information, the mechanisms underlying these interactions are not well understood. Moreover, prior studies that have examined face learning and recognition are constrained in their generalisability due to experimental designs or the selection of test stimuli. In this thesis, the interaction between three face processes – unfamiliar face matching, face learning, and face recognition – and contextual information are investigated to improve understanding of how context modulates face identity decisions. In Chapter 2, I examined an applied unfamiliar face matching task, where participants assumed the role of a surveillance officer required to match the names and faces of individuals entering a work building. Participants were more likely to declare that pairs of faces are a “match” when preceding name pairs are a “match”, and this effect remained even when participants were instructed to disregard name information in their decision-making. In Chapter 3, I examined face learning, where participants were presented with facial identities across multiple learning phases on either the same or different visual backgrounds. While facial variability had an influence on learning and recognition accuracy for two of the four studies, contextual variability had no effect on face learning, regardless of whether facial images or Zoom videos were used as learning stimuli. Finally, in Chapter 4, across my face recognition studies, I adapted a semantic priming study to investigate whether contextual information would be able to prime the recognition of familiar faces. I found that priming using either written or scene-based contextual information did not influence the speed at which individuals recognised familiar faces. The mechanisms utilised in each of these three face processes are discussed and compared with prevailing theories of face processing and contextual information in familiar face recognition (IAC model) and sensory systems more generally (predictive coding hypotheses).