This thesis investigated the effect of visuomotor and working memory 1) task difficulty and 2) multitasking on dynamic functional connectivity in the brain. Studies have only recently begun to investigate functional connectivity within the scope of concurrent dual task or varying task difficulty conditions (Cocchi, Zalesky, et al. 2011; Rietschel et al. 2012). A series of EEG recordings were conducted during execution of visuomotor or working memory tasks within a novel paradigm using BCI2VR custom MATLAB toolbox. Functional connectivity was correlated with task-related coherence (TRCoh) analysis between two task conditions involving either variation in task difficulty or concurrent execution during multitasking within the delta (0 – 4 Hz), theta (4 – 8 Hz), alpha (8 – 12 Hz), beta1 (12-16 Hz), beta2 (16 – 20 Hz) and beta3 (20 – 24 Hz) frequency bands. An increase in coherence was observed with increased cognitive load, during both increased task difficulty and multitasking, in all frequency bands except beta1 and beta2. This may suggest that the psychomotor efficiency hypothesis also applies to multitasking as well as task difficulty. Decreases in beta coherence were observed with increased performance error, indicating that interregional beta coherence may not follow the PEH trend. The increased coherence between brain regions in the alpha, delta and theta bands contributes to the growing volume of research on quantifying cognitive workload and may serve as a future basis on increasing multitasking efficiency during high stress environments. Further research recording multitasking effects on individuals over regular intervals during an extended period of time (months or years) will be required to better understand changes in functional connectivity within the brain.

It has been consistently shown in the literature that when gaze is directed to a specific location, for a long enough duration, at the correct time relative to the motor execution, high-levels of performance are possible. In recent years, a particular gaze called quiet eye (QE) has gained growing attention among researchers investigating aiming tasks and has become accepted within the literature as a measure of optimal attentional control. Previous studies consistently displayed that longer QE is associated with superior performance however there is lack of understanding how QE exerts its positive effect on performance. Therefore the overriding aim of the current program of research was to explore the mechanisms behind the QE by experimentally manipulating the separate aspects of the QE definition in ways that have not been explored by previous researchers. In study 1 (Chapter 2), two experiments were conducted to examine the key characteristics of the QE in golf putting; duration and location. Novice participants were randomly allocated to training groups of experimentally longer or shorter QE durations (experiment 1) and training groups of different QE locations (experiment 2). A retention-pressure-retention design was adopted, and measures of performance and QE were recorded. All groups improved performance after training and the levels of performance achieved were robust in a pressure test. However there were no significant group effects. Study 1 provided partial support for the efficacy of QE training, but did not clarify how the QE itself underpins the performance advantage revealed in earlier studies and suggested that the QE should perhaps not be reported simply as a function of its duration or its location. In study 2 (Chapter 3) an examination of the timing of the QE was performed, using an occlusion paradigm. This provided an experimental manipulation of the availability of visual information during the putting action. Expert participants performed a putting task under three different conditions, namely full, early, and late vision conditions. The results showed that putting accuracy was the poorest when late visual information was occluded (early vision condition). Therefore study 2 suggested that the correct temporal placement of gaze might be more crucial to successful performance, and that putting accuracy was poorer when the latter component of QE which ensures precise control of movement was occluded. Previous research has revealed that anxiety can attenuate the QE duration, shortening the latter component which was shown to be important in study 2. Therefore the final study in the thesis examined the influence of anxiety on attentional control (QE). Expert golfers participated in a putting shootout competition designed to increase levels of anxiety and continued putting until a missed putt occurred. The results revealed that duration of QE was shorter on the missed putt, while there was no difference in QE duration for successful putts (first and penultimate putts). The results are therefore supportive of the predictions of attentional control theory. Furthermore this reduction in QE duration was result of latter component of QE being attenuated, supporting models of motor control that point to the importance of online visual information for regulating control of movements. The results of this series of studies conclude that the timing of the QE – maintaining a steady fixation through the unfolding movement to ensure precise online control - seems to be the strong candidate for how QE exerts a positive effect on performance.

This research study examined motor control and procedural learning abilities in the oral and manual motor systems of adults who stutter, using people with Parkinson's disease, and age-matched controls as comparison groups. Participants in this study were asked to track a moving target on a computer screen with their jaw and with their dominant hand. Specifically, we compared their tracking accuracy for predictable and unpredictable signals. Procedural learning (defined as increased accuracy over time) was assessed by examining changes in tracking accuracy within a single tracking trial and between consecutive tracking trials of the same predictable condition. There were two main findings in this study related to tracking accuracy and procedural learning in people who stutter (PWS) and age-matched controls (CPWS). First, our analyses revealed that there was no significant difference between PWS and CPWS in the accuracy of tracking of either predictable or unpredictable conditions for either the hand or the jaw, although a trend was observed in which PWS performed more poorly in both for decreased accuracy. Second, both PWS and CPWS showed evidence of procedural learning to the same extent. There were two main findings in this study related to tracking accuracy and procedural learning in people who have Parkinson's disease (PPD) and age-matched controls (CPPD). First, tracking accuracy analyses revealed that PPD performed significantly more poorly than CPPD during jaw tracking of predictable conditions, but they were not significantly different from CPPD in jaw tracking of unpredictable conditions. During hand tracking PPD differed significantly from CPPD in tracking of both predictable and unpredictable conditions for their less accurate performance. Second, there was no significant difference between the two groups in the extent of procedural learning during jaw tracking. However, during hand tracking the PPD group improved less with time than the CPPD, suggesting that the PPD group had reduced procedural learning ability in the manual motor domain. Lastly, age was found to be an important factor determining tracking accuracy in our participants. Younger participants (PWS and CPWS) in the age range of 18-40 years had significantly better accuracy of jaw and hand tracking than the older individuals (PPD and CPPD) in the age range of 57-79 years.

‘Sensorimotor transformations’ are processes whereby sensory information is used to generate motor commands. One example is the ‘visuomotor map’ that transforms visual information about objects to motor commands that activates various muscles during grasping movements. In the first study we quantified the relative impact (or ‘weighting’) of visual and haptic information on the sensorimotor transformation and investigated the principles that regulates the weighting process. To do this, we let subjects perform a task in which the object seen (visual object) and the object grasped (haptic object) were physically never the same. When the haptic object became larger or smaller than the visual object, subjects in the following trials automatically adapted their maximum grip aperture (MGA) when reaching for the object. The adaptation process was quicker and relied more on haptic information when the haptic objects increased in size than when they decreased in size. As such, sensory weighting is molded to avoid prehension error. In the second study we investigated the degree to which the visuomotor map could be modified. Normally, the relationship between the visual size of the object (VO) and the MGA can be expressed as a linear relationship, where MGA = a + b * VO. Our results demonstrate that subjects inter- and extrapolate in the visuomotor map (that is, they are reluctant to abandon the linear relationship) and that the offset (a) but not the slope (b) can be modified. In the third study, we investigated how a ‘new’ sensorimotor transformation can be established and modified. We therefore replaced the normal input of visual information about object size with auditory information, where the size of the object was log-linearly related to the frequency of a tone. Learning of an audiomotor map consisted of three distinct phases: during the first stage (~10-15 trials) there were no overt signs of learning. During the second stage there was a period of fast learning where the MGA became scaled to the size of the object until the third stage where the slope was constant. The purpose of the fourth study was to investigate the sensory basis for the aperture adaptation process. To do that, the forces acting between the fingertips and the object was measured as the subjects adapted. Our results indicate that information about when the fingers contacts the object, that is, the ‘timing’ of contact, is likely to be used by the CNS to encode an unexpected object size. Since injuries and disease can affect the sensorimotor transformations that controls the hand, knowledge about how these processes are established and modified may be used to develop techniques for sensory substitution and other rehabilitation strategies.

Movement is essential to human life because it provides us with the freedom of mobility and the power to affect our surroundings. Moreover, movements are vital to communication: from hand and finger movements when writing, mouth and throat movements when speaking, to painting, dancing, and other forms of artistic self expression. As people grow and experience new environments, adaptively maintaining the accuracy of movements is a critical function of the motor system. In this dissertation, I explore the key mechanisms that underlie the adaptability of simple visually guided reaching movements. I specifically focus on two key facets of this adaptability: how motor learning rate can be predicted by motor variability and how motor learning affects the mechanisms which underlie movement planning. Inspired by reinforcement learning, I hypothesized that greater amounts of motor variability aligned with a task will produce more effective exploration, leading to faster learning rates. I discovered that this relationship predicts person-to-person and task-to-task differences in learning rate for both reward-based and error-based learning tasks. Moreover, I found that the motor system actively and enduringly reshapes motor output variability, aligning it with a task to improve learning. These results indicate that the structure of motor variability is an activelyregulated, critical feature of the motor system which plays a fundamental role in determining motor learning ability. Combining prominent theories in motor control, I created a model which describes the planning of visually guided reaching movements. This model computes a weighted average of two independent feature-based motor plans: one based on the goal location of a movement, and the other based on an intended movement vector. Employing this model to characterize the generalization of adaptation to movements and movement sequences, I find that both features, movement vector and goal location, contribute significantly to movement planning, and that each feature is remapped by motor adaptation. My results show that multiple features contribute to the planning of both point-to-point and sequential reaching movements. Moreover, a computational model which is based on the remapping of multiple features accurately predicts how visuomotor adaptation affects the planning of movement sequences. / Engineering and Applied Sciences

The philosophical and scientific studies of consciousness are two disciplines having much to learn from one another. On the one hand, a science of consciousness involves taking an objective approach to what is essentially a subjective phenomenon, giving rise to tricky conceptual and methodological issues, ones an analytic philosopher is perhaps best equipped to handle. On the other hand, a wealth of data now exists concerning the neural basis of consciousness. Such data, interpreted properly, can confirm or disconfirm philosophical views on consciousness, helping adjudicate debates thus far intractable. This dissertation explores some ways in which the philosophy and science of consciousness can be of mutual benefit to one another.

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229 pages

abstract: Adapting to one novel condition of a motor task has been shown to generalize to other naïve conditions (i.e., motor generalization). In contrast, learning one task affects the proficiency of another task that is altogether different (i.e. motor transfer). Much more is known about motor generalization than about motor transfer, despite of decades of behavioral evidence. Moreover, motor generalization is studied as a probe to understanding how movements in any novel situations are affected by previous experiences. Thus, one could assume that mechanisms underlying transfer from trained to untrained tasks may be same as the ones known to be underlying motor generalization. However, the direct relationship between transfer and generalization has not yet been shown, thereby limiting the assumption that transfer and generalization rely on the same mechanisms. The purpose of this study was to test whether there is a relationship between motor generalization and motor transfer. To date, ten healthy young adult subjects were scored on their motor generalization ability and motor transfer ability on various upper extremity tasks. Although our current sample size is too small to clearly identify whether there is a relationship between generalization and transfer, Pearson product-moment correlation results and a priori power analysis suggest that a significant relationship will be observed with an increased sample size by 30%. If so, this would suggest that the mechanisms of transfer may be similar to those of motor generalization. / Dissertation/Thesis / Masters Thesis Biomedical Engineering 2018

Visuomotor behaviour – from handling simple objects to operating complex devices – is of fundamental importance in our everyday lives, yet there is relatively little evidence as to how healthy ageing affects these processes. A central role is played by the human capacity for reaching and grasping. Grasping an object requires complex visuomotor transformations, including processing of the object’s extrinsic features (it’s spatial location) and intrinsic features (such as size and shape). It has been documented that action relevant intrinsic object properties automatically facilitate specific motor actions despite being task-irrelevant, the so-called object affordance effect. These effects have been demonstrated for (1) grasp type (precision and power grips being facilitated by small and large objects) and (2) object-orientation (whereby right and left handed grasps are facilitated by object-orientation), and might underlie the effortlessness with which humans can interact with objects. Yet, these paradigms have not previously been employed in the study of healthy ageing, and little is known concerning how these processes change over the life span. Elucidating these changes is of particular importance as age-related degeneration of white matter integrity is well documented. Consequently, if successful visuomotor behaviour relies on white matter integrity, age-related reductions in affordance effects should be observed. This prediction was tested in a series of experiments. Experiment 1 investigated age-differences in object-size compatibility effects, and results corroborated our prediction of age-related reductions in object-size effects. Experiment 2 investigated age-differences in (1) spatial compatibility effects versus object-orientation effects, and (2) the locus of the effects (facilitation versus interference effects). Results revealed (1) some evidence of larger affordance than spatial effects in both age-groups, and (2) interference effects in the younger group and both facilitation and interference effects in the older group, showing a potential change in processing modes or strategies. Experiments 3 and 4 addressed the main competing account, the attention-directing hypothesis (according to which attentional shifts are responsible for the generation of automatic response codes, rather than the affects arising from afforded actions), by using a novel stimulus set in which such attentional differences can be ruled out. Results provided strong evidence in favour of the object-size affordance hypothesis. A final neuroimaging experiment investigated age-differences in the object-size effect and its neural correlates by combining behavioural, functional MRI and diffusion tensor imaging (DTI) data. Results revealed evidence of age-differences, both on the behavioural and functional level. For the DTI data, we investigated all four diffusion metrics (something which is not frequently reported in the healthy ageing literature), and found widespread age-related differences in white matter integrity. The empirical findings presented in this thesis offer a significant contribution to ageing research, by further elucidating the relationship between age-related neurophysiological changes and visuomotor behaviour. The overall picture which emerged from this series of experiments was consistent with our prediction of age-related reductions in affordance effects. Furthermore, it is likely that these age-differences may have, at least in part, a neurophysiological basis.