Stochastic neural network dynamics: synchronisation and control

Biological brains exhibit many interesting and complex behaviours. Understanding of the mechanisms behind brain behaviours is critical for continuing advancement in fields of research such as artificial intelligence and medicine. In particular, synchronisation of neuronal firing is associated with both improvements to and degeneration of the brain’s performance; increased synchronisation can lead to enhanced information-processing or neurological disorders such as epilepsy and Parkinson’s disease. As a result, it is desirable to research under which conditions synchronisation arises in neural networks and the possibility of controlling its prevalence. Stochastic ensembles of FitzHugh-Nagumo elements are used to model neural networks for numerical simulations and bifurcation analysis. The FitzHugh-Nagumo model is employed because of its realistic representation of the flow of sodium and potassium ions in addition to its advantageous property of allowing phase plane dynamics to be observed. Network characteristics such as connectivity, configuration and size are explored to determine their influences on global synchronisation generation in their respective systems. Oscillations in the mean-field are used to detect the presence of synchronisation over a range of coupling strength values. To ensure simulation efficiency, coupling strengths between neurons that are identical and fixed with time are investigated initially. Such networks where the interaction strengths are fixed are referred to as homogeneously coupled. The capacity of controlling and altering behaviours produced by homogeneously coupled networks is assessed through the application of weak and strong delayed feedback independently with various time delays. To imitate learning, the coupling strengths later deviate from one another and evolve with time in networks that are referred to as heterogeneously coupled. The intensity of coupling strength fluctuations and the rate at which coupling strengths converge to a desired mean value are studied to determine their impact upon synchronisation performance. The stochastic delay differential equations governing the numerically simulated networks are then converted into a finite set of deterministic cumulant equations by virtue of the Gaussian approximation method. Cumulant equations for maximal and sub-maximal connectivity are used to generate two-parameter bifurcation diagrams on the noise intensity and coupling strength plane, which provides qualitative agreement with numerical simulations. Analysis of artificial brain networks, in respect to biological brain networks, are discussed in light of recent research in sleep theor

Experimental and numerical analysis of a pivoted cylinder subjected to vortex-induced vibrations

This thesis presents and discusses the results of two investigations. The first involves studying wake dynamics along the span of a pivoted cylinder undergoing vortex-induced vibrations (VIV) and its relationship with the structural response. This experiment used planar Particle Image Velocimetry and image-based tracking techniques to measure the wake and cylinder response at different flow velocities. The second investigation assesses the accuracy of a two-dimensional representation of the first experimental study using RANS models based on the k-w turbulence model. A prior experiment of a bottom-fixed cylinder undergoing VIV was performed to analyse its variable amplitude condition in preparation for the pivoted cylinder case. The pivoted cylinder results showed maximum amplitudes of approximately half and two times its diameter along and perpendicular to the flow direction, respectively. Similar to the bottom-fixed cylinder, the maximum response was achieved when the cylinder motion and vortex shedding frequencies were equal (i.e., synchronised) to the natural frequency of the structure in water, and when this equivalence was preserved along the cylinder span. At higher flow velocities, a desynchronised region appeared at the water surface, different from the previously observed bottom-up desynchronisation of the bottom-fixed cylinder. Wake measurements closer to the water surface had a broader wake width, higher momentum transference, and higher vortex strength compared to lower water depths. The local response along the cylinder span could not fully explain these differences. The numerical model reached amplitudes that were 40% lower than the experimental results. Moreover, bistable responses were observed in the upper branch and not in the experimental results. The tested numerical model was insufficient to account for the three-dimensional component of the pivoted cylinder. Additional research is needed to understand the cylinder-wake dynamics of the pivoted cylinder, especially related to its synchronisation-desynchronisation process, to improve the prediction capabilities of two-dimensional numerical models

Keep calm and age well: Behavioural and electrophysiological investigations into the effects of cumulative stress exposure on ageing cognition

The research presented in this thesis comprises a body of work dedicated to continuing and enriching past exploration into the impact cumulative life stress exerts on ageing cognition. In order to extend previous work into this topic, behavioural measures were paired with electroencephalographic recordings of the cortical oscillatory activity thought to underlie cognitive operations. In a theoretical sense, work presented in this thesis strengthens past investigations highlighting the adverse effects of life stress on elderly peoples’ working memory abilities by replicating the effect under conditions of increased experimental rigour. It further provides evidence that the detrimental effects of cumulative stress extend to the domains of executive control and spatial memory. Electrophysiological findings obtained during task execution and at rest indicate pronounced changes in the oscillatory activity of aged high stress individuals’ delta, theta, alpha and gamma bands and are thus the first to demonstrate that cumulative stress affects the underlying neural processes related to successful task execution. As such, from a methodological standpoint, the current research strongly advocates the use of neuroscientific tools such as the electroencephalogram to gain an increased understanding of the mechanisms by which increased stress exposure evokes progressive cognitive decline in old age. Combined, the work presented in this thesis demonstrates the negative consequences of leading a highly stressful life for the integrity of multiple cognitive functions in old age and is the first to provide an indication of how cumulative stress affects both cortical and (indirectly) subcortical regions of the brain necessary for successful cognitive functioning

A brain-computer interface integrated with virtual reality and robotic exoskeletons for enhanced visual and kinaesthetic stimuli

Brain-computer interfaces (BCI) allow the direct control of robotic devices for neurorehabilitation and measure brain activity patterns following the user’s intent. In the past two decades, the use of non-invasive techniques such as electroencephalography and motor imagery in BCI has gained traction. However, many of the mechanisms that drive the proficiency of humans in eliciting discernible signals for BCI remains unestablished. The main objective of this thesis is to explore and assess what improvements can be made for an integrated BCI-robotic system for hand rehabilitation. Chapter 2 presents a systematic review of BCI-hand robot systems developed from 2010 to late 2019 in terms of their technical and clinical reports. Around 30 studies were identified as eligible for review and among these, 19 were still in their prototype or pre-clinical stages of development. A degree of inferiority was observed from these systems in providing the necessary visual and kinaesthetic stimuli during motor imagery BCI training. Chapter 3 discusses the theoretical background to arrive at a hypothesis that an enhanced visual and kinaesthetic stimulus, through a virtual reality (VR) game environment and a robotic hand exoskeleton, will improve motor imagery BCI performance in terms of online classification accuracy, class prediction probabilities, and electroencephalography signals. Chapters 4 and 5 focus on designing, developing, integrating, and testing a BCI-VR-robot prototype to address the research aims. Chapter 6 tests the hypothesis by performing a motor imagery BCI paradigm self-experiment with an enhanced visual and kinaesthetic stimulus against a control. A significant increase (p = 0.0422) in classification accuracies is reported among groups with enhanced visual stimulus through VR versus those without. Six out of eight sessions among the VR groups have a median of class probability values exceeding a pre-set threshold value of 0.6. Finally, the thesis concludes in Chapter 7 with a general discussion on how these findings could suggest the role of new and emerging technologies such as VR and robotics in advancing BCI-robotic systems and how the contributions of this work may help improve the usability and accessibility of such systems, not only in rehabilitation but also in skills learning and education

Modulating application behaviour for closely coupled intrusion detection

Includes bibliographical references.This thesis presents a security measure that is closely coupled to applications. This distinguishes it from conventional security measures which tend to operate at the infrastructure level (network, operating system or virtual machine). Such lower level mechanisms exhibit a number of limitations, amongst others they are poorly suited to the monitoring of applications which operate on encrypted data or the enforcement of security policies involving abstractions introduced by applications. In order to address these problems, the thesis proposes externalising the security related analysis functions performed by applications. These otherwise remain hidden in applications and so are likely to be underdeveloped, inflexible or insular. It is argued that these deficiencies have resulted in an over-reliance on infrastructure security components

Applied and laboratory-based autonomic and neurophysiological monitoring during sustained attention tasks

Fluctuations during sustained attention can cause momentary lapses in performance which can have a significant impact on safety and wellbeing. However, it is less clear how unrelated tasks impact current task processes, and whether potential disturbances can be detected by autonomic and central nervous system measures in naturalistic settings. In a series of five experiments, I sought to investigate how prior attentional load impacts semi-naturalistic tasks of sustained attention, and whether neurophysiological and psychophysiological monitoring of continuous task processes and performance could capture attentional lapses. The first experiment explored various non-invasive electrophysiological and subjective methods during multitasking. The second experiment employed a manipulation of multitasking, task switching, to attempt to unravel the negative lasting impacts of multitasking on neural oscillatory activity, while the third experiment employed a similar paradigm in a semi-naturalistic environment of simulated driving. The fourth experiment explored the feasibility of measuring changes in autonomic processing during a naturalistic sustained monitoring task, autonomous driving, while the fifth experiment investigated the visual demands and acceptability of a biological based monitoring system. The results revealed several findings. While the first experiment demonstrated that only self-report ratings were able to successfully disentangle attentional load during multitasking; the second and third experiment revealed deficits in parieto-occipital alpha activity and continuous performance depending on the attentional load of a previous unrelated task. The fourth experiment demonstrated increased sympathetic activity and a smaller distribution of fixations during an unexpected event in autonomous driving, while the fifth experiment revealed the acceptability of a biological based monitoring system although further research is needed to unpick the effects on attention. Overall, the results of this thesis help to provide insight into how autonomic and central processes manifest during semi-naturalistic sustained attention tasks. It also provides support for a neuro- or biofeedback system to improve safety and wellbeing

Sound of Violent Images / Violence of Sound Images: Pulling apart Tom and Jerry

Violence permeates Tom and Jerry in the repetitive, physically violent gags and scenes of humiliation and mocking, yet unarguably, there is comedic value in the onscreen violence.The musical scoring of Tom and Jerry in the early William Hanna and Joseph Barbera period of production (pre-1958) by Scott Bradley played a key role in conveying the comedic impact of violent gags due to the close synchronisation of music and sound with visual action and is typified by a form of sound design characteristic of zip crash animation as described by Paul Taberham (2012), in which sound actively participates in the humour and directly influences the viewer’s interpretation of the visual action. This research investigates the sound-image relationships in Tom and Jerry through practice, by exploring how processes of decontextualisation and desynchronisation of sound and image elements of violent gags unmask the underlying violent subtext of Tom and Jerry’s slapstick comedy. This research addresses an undertheorised area in animation related to the role of sound-image synchronisation and presents new knowledge derived from the novel application of audiovisual analysis of Tom and Jerry source material and the production of audiovisual artworks. The findings of this research are discussed from a pan theoretical perspective drawing on theorisation of film sound and cognitivist approaches to film music. This investigation through practice, supports the notion that intrinsic and covert processes of sound-image synchronisation as theorised by Kevin Donnelly (2014), play a key role in the reading of slapstick violence as comedic. Therefore, this practice-based research can be viewed as a case study that demonstrates the potential of a sampling-based creative practice to enable new readings to emerge from sampled source material. Novel artefacts were created in the form of audiovisual works that embody specific knowledge of factors related to the reconfiguration of sound-image relations and their impact in altering viewers’ readings of violence contained within Tom and Jerry. Critically, differences emerged between the artworks in terms of the extent to which they unmasked underlying themes of violence and potential mediating factors are discussed related to the influence of asynchrony on comical framing, the role of the unseen voice, perceived musicality and perceptions of interiority in the audiovisual artworks. The research findings yielded new knowledge regarding a potential gender-based bias in the perception of the human voice in the animated artworks produced. This research also highlights the role of intra-animation dimensions pertaining to the use of the single frame, the use of blank spaces and the relationship of sound-image synchronisation to the notion of the acousmatic imaginary. The PhD includes a portfolio of experimental audiovisual artworks produced during the testing and experimental phases of the research on which the textual dissertation critically reflects

One path or two: Could differential grammatical class processing reflect human language evolution?

The fundamentally transient nature of human speech and sign means that there is no direct fossil record to document the emergence of language. As a result, theories of language evolution have traditionally relied on educated guesswork informed by child language acquisition studies and comparisons with other species' vocal communication systems. More recently, however, more refined language evolution models have been proposed from three general perspectives: the proto-speech model which assumes that spoken language first emerged as a communicative system in humans; the proto-sign model which broadly assumes that language first emerged in the form of manual gesture; and the mixed or co-evolution model which posits both sound and gesture components. Although there is a vast pool of literature examining the neural bases of modern human language which has, in turn, been interpreted from a language evolution perspective, many of these studies have used methodologies which could have potentially confounded results. The current thesis was therefore firstly designed to address such concerns by establishing a corpus of experimental stimulus words in which both cognitive and acoustic properties were quantified and therefore controllable. Having thus established this corpus, electroencephalography (EEG) was recorded from 30 human participants as they undertook (i) a passive listening task involving animal vocalisations and (ii) a grammatical decision/learning task (nouns versus verbs) using real and nonsense human speech stimuli. Results suggested that within the adult human brain, changes in both the lower (8 - 10 Hz) and upper (10 - 12 Hz) alpha EEG range reflect functional differences in the processing of complex communicative sound strings, with spoken noun and verb stimuli showing clearly distinct patterns of information processing flow. Of note, the left frontal eye field appears to process verb but not noun stimuli on-the-fly. Furthermore, differences in grammatical class processing (nouns versus verbs) appear to occur early