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Vision is important for the control of upper limb movements (Woodworth, 1899). How and when vision is used during a limb movement continues to be debated. In this thesis, I examined the use of visual feedback as a function of retinal limb position. Individuals made rapid upper limb aiming movements to a target location and vision was provided when the limb was at varying degrees of retinal eccentricity. The temporal characteristics, endpoint accuracy and precision, as well as the spatial variability of the limb trajectories were recorded and analyzed. No relationship was observed between retinal limb positions and the use of visual feedback during the movements. These results suggest that the use of vision during limb movements is not directly tied to the neuroanatomy of the eye and challenges continuous models of upper limb control.

Vision is important for the control of upper limb movements (Woodworth, 1899). How and when vision is used during a limb movement continues to be debated. In this thesis, I examined the use of visual feedback as a function of retinal limb position. Individuals made rapid upper limb aiming movements to a target location and vision was provided when the limb was at varying degrees of retinal eccentricity. The temporal characteristics, endpoint accuracy and precision, as well as the spatial variability of the limb trajectories were recorded and analyzed. No relationship was observed between retinal limb positions and the use of visual feedback during the movements. These results suggest that the use of vision during limb movements is not directly tied to the neuroanatomy of the eye and challenges continuous models of upper limb control.

Canine cadaveric forelimbs (136) were randomly assigned to either treatment (aiming device) or control (fluoroscopic-guided) groups, and to either diplomate or resident for humeral transcondylar screw placement. Each limb underwent a transcondylar humeral screw placement from a lateral to medial direction. Digital radiography was used to evaluate screw trajectory, measured as deviation from the epicondylar line, and eccentricity on the humeral condyle. Procedure time, difference in outcome based on experience level, and complications were recorded. In the right limb, screw trajectory with the aiming device was decreased compared to fluoroscopy. There was no difference of accuracy between leg laterality with fluoroscopy. Screw trajectory was increased with resident versus diplomate procedures. Eccentricity deviation was decreased in fluoroscopy groups. The findings of this current study suggest that the universal aiming device produced accurate transcondylar screws with comparable results to fluoroscopic- guided methods.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Concentrating solar power as a sustainable energy technology is considered favourable in South Africa due to the high solar resource and the integration possibilities with the current electricity grid. Considering the various concentrating solar power technologies, the central receiver system is thought to be one of the most promising due to its high capacity factor and cost-efficient thermal storage capabilities. These thermal systems are able to reach high temperatures (more than 1000°C have been shown), and to obtain such temperatures, a high solar flux is required. This is achievable by aiming all of the heliostats at the centre of the target. High flux gradients over the receiver surface area and between the outer and inner surfaces of the receiver material can exist. These thermal gradients account for differences in temperatures on the receiver which result in thermal stresses leading to elastic and potentially plastic deformation of the material. To eradicate the thermal stresses, the aim points of the heliostats can be managed such that the flux density distribution over the receiver aperture is decreased and homogenised. The primary objective of this thesis is to develop an aiming strategy specifically for small experimental heliostat fields. To reach this objective, a simulation platform was developed to model any heliostat field and receiver, and an analysis was conducted to compare analytical flux prediction methods to ray tracing. At high incidence angles of between 30° and 60°, the standard deviations of the circular Gaussian flux approximation methods were found to differ between approximately 10 % and 30 % from the ray traced results. A novel method, the Gaussian mixture model, was suggested and deviated less than 4 % from the ray traced results when considering the standard deviation of the flux profile. Two basic aiming strategies were developed using the Tabu search and Genetic algorithm optimisation methods. These two strategies make use of approximate method of flux prediction. Experiments were conducted to investigate static aiming strategies on physical systems and to identify factors that could have an effect on the experimental results. Finally a method of implementing the aiming strategy on a dynamic system was proposed. By implementing both optimisation methods to complement each other, a new aiming strategy was developed that proved to provide better homogenisation of the flux distribution than either of the two methods alone. The accuracy of the final predicted flux distribution was improved by using the Gaussian mixture model as the flux distribution approximation method. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonenergie as ’n hernubare energie bron, word in Suid-Afrika as uitvoerbaar beskou weens die hoë stralingsdigtheid asook die moontlikheid om hierdie tegnologie te koppel aan die huidige energienetwerk. As die verskeie gekonsentreerde sonenergie tegnologieë in ag geneem word, word sentrale ontvangerstelsels beskou as die mees belowende sonenergie konsep as gevolg van die hoë energie kapasiteit en die vermoë om termiese energie te stoor. Hierdie termiese stelsels besit die vermoë om hoë temperature te bereik (meer as 1000°C is al opgemerk), en om hierdie temperature te verkry word ’n hoë termiese vloed benodig. Dit is bereikbaar deur al die heliostate op die middel van die ontvanger te rig. Hoë termiese vloedgradiënte oor die oppervlakte van die opvanger en tussen die buite- en binne laag van die opvanger materiaal kan ontstaan. Termiese vloedgradiënte kan verskille in temperatuur op die ontvanger veroorsaak wat termiese spanning tot gevolg het kan lei tot elastiese en potensieel plastiese vervorming van die materiaal. Omvan die termiese spanning ontslae te raak kan die heliostate deur beheerstelsels na ander dele van die ontvanger gerig word om sodoende ’n laer en meer egalige termiese vloed oor die oppervlak van die ontvanger te verkry. Die hoofdoel van hierdie tesis is die ontwikkeling van ’n mikstrategie, hoofsaaklik bedoel vir klein eksperimentele heliostaatvelde. Om hierdie hoofdoel te bereik, was ’n simulasieplatform ontwikkel waardeur heliostaatvelde en opvangerstelsels gemodelleer kan word, en ’n analise is gedoen om die verskeidenheid benaderende analitiese metodes te vergelyk met die straalopsporingsmetode. By hoë invalshoeke tussen 30° en 60° is daar gevind dat die benaderende modelle wat die termiese vloed as ’n normale Gaussiese verspreiding beskou, ’n afwyking van die straalopsporingsresultate toon van ongeveer 10 % tot 30 %. ’n Nuwe metode, die Gaussiese mengsel model, was voorgestel en het minder as 4 % van die straalopsporings resultate afgewyk, met die standaard afwyking van die termiese vloed profiel in ag geneem. Twee basiese mikstrategieë is ontwikkel deur gebruik te maak van die Tabu soek en Genetiese algoritme optimeringsmetodes. Hierdie strategieë maak gebruik van die benaderende metodes om termiese vloed te voorspel. Eksperimente is uitgevoer om die implementering van statiese mikstrategieë op ’n fisiese stelsel te beskou en die faktore wat ’n invloed op die eksperimentele resultate sal hê te identifiseer. Ten laaste word ’n metode voorgestel vir die implementering van die mikstrategieë op ’n dinamiese stelsel. Deur beide optimeringsmetodes te implementeer sodat hul mekaar komplimenteer, word ’n nuwe mikstrategie ontwikkel wat beter homogenisering van die termiese vloed verspreiding bewys het as enige van die alleen staande metodes. Die akkuraatheid van die finale voorgestelde termiese vloed verspreiding was verbeter deur gebruik te maak van die Gaussiese mengsel model as die benaderende metode van die termiese vloed verspreiding.

When player skill levels differ widely in a competitive First-Person Shooter (FPS) game, enjoyment suffers: weaker players become frustrated and stronger players become less engaged. Player balancing techniques attempt to assist the weaker player and make games more competitive, but these techniques have limitations for deployment when skill levels vary substantially. In this thesis, we developed new player balancing schemes to deal with a range of FPS skill difference, and tested these techniques in a series of five studies using a commercial-quality FPS game developed with the UDK engine. Our results showed that our balancing techniques (Combo and Delay) are extremely effective at balancing, even for players with large skill differences. These techniques also led to higher enjoyment of the game by players of all skill levels. Our studies are the first to show that player balancing can work well in realistic FPS games, providing developers with a way to increase the audience for this popular genre. In addition, our results demonstrate the idea that successful balancing is as much about the way the technique is applied as it is about the specific manipulation.

The current study evaluated whether robotic guidance can influence movement planning and/or the use of online proprioceptive feedback. Participants were divided into three groups wherein they practiced an aiming task unassisted or via a robotic device that led them through a trajectory with an asymmetric or symmetric velocity profile. Baseline performance was measured prior to training and a post-test included control and tendon vibration trials. Temporal, spatial, and kinematic variables were used to assess planning and online control mechanisms. Results indicated that tendon vibration altered the way individuals planned their movements and used online sensory feedback. Robotic-guided groups appeared to use online feedback to a lesser extent than the unassisted group during tendon vibration trials, based on kinematic data. Individuals may become less inclined to use erroneous proprioceptive feedback following robotic guidance, supporting the potential benefit of robotics in neuro-motor rehabilitation for those with proprioceptive deficits.

The current study evaluated whether robotic guidance can influence movement planning and/or the use of online proprioceptive feedback. Participants were divided into three groups wherein they practiced an aiming task unassisted or via a robotic device that led them through a trajectory with an asymmetric or symmetric velocity profile. Baseline performance was measured prior to training and a post-test included control and tendon vibration trials. Temporal, spatial, and kinematic variables were used to assess planning and online control mechanisms. Results indicated that tendon vibration altered the way individuals planned their movements and used online sensory feedback. Robotic-guided groups appeared to use online feedback to a lesser extent than the unassisted group during tendon vibration trials, based on kinematic data. Individuals may become less inclined to use erroneous proprioceptive feedback following robotic guidance, supporting the potential benefit of robotics in neuro-motor rehabilitation for those with proprioceptive deficits.

<p> Four experiments were conducted to examine the visual regulation of manual aiming under visually displaced conditions. A secondary purpose of these studies was to examine potential gender differences in behaviour following prismatic displacement. The initial experiment was designed to test a monocular switch of vision as a method of presenting the visually displaced information. This experiment also provided an opportunity to explore manual and ocular asymmetries. The monocular switch had no major influence on the terminal accuracy of the movements. Therefore. the methodology was employed to present visually displaced information in the three subsequent experiments. The second experiment was designed to present visually displaced information at different times during the aiming movements. while the third experiment was designed to remove the displaced information during the movements. In a fourth experiment. a real time movement analysis procedure was used to introduce visual displacement at various kinematic markers. In Experiments 2, 3, and 4. the early presentation and removal of the visually displaced information had the most influence on terminal accuracy. However. these effects were not consistent across gender. Male participants executed their movements based on the information presented prior to the movements. In contrast. female participants were more influenced by the information received during the initial portions of the movements. The results support models of manual control that emphasize the importance of vision in the early portions of the movement for the correction of trajectory errors. The effects involving gender suggest that gender should be included as an independent variable in future research. </p> / Thesis / Master of Science (MSc)

The Remote Distractor Effect (RDE) is a robust phenomenon where a saccade to a lateralised target is delayed by the appearance of a distractor in the contralateral hemifield (Walker, Kentridge, & Findlay, 1995). The main aim of this thesis was to test whether the RDE generalises to response modalities other then the eyes. In Chapter 2, the RDE was tested on saccadic and simple manual keypress responses, and on a choice discrimination task requiring a covert shift of attention. The RDE was observed for saccades, but not simple manual responses, suggesting that spatially oriented responses may be necessary for the phenomenon. However, it was unclear whether distractor interference occurred in the covert task. Chapter 4 compared the effects of distractors between spatially equivalent tasks requiring saccadic and manual aiming responses respectively. Again, the RDE was observed for the eyes but not for the hands. This dissociation was also replicated in a more naturalistic task in which participants were free to move their eyes during manual aiming. In order to examine the time-course of distractor effects for the eyes and the hands, a third experiment investigated distractor effects across a wider range of target-distractor delays, finding no RDE for manual aiming responses at distractor delays of 0, 100, or 150 ms. The failure of the RDE to generalise to manual aiming suggests that target selection mechanisms are not shared between hand and eye movements. Chapter 5 further investigated the role of distractors during covert discrimination. The first experiment showed that distractor appearance did not interfere with discrimination performance. A second experiment, in which participants were also asked to saccade toward the target, confirmed the lack of RDE for covert discrimination while saccades were slower in distractor trials. The dissociation between covert and overt orienting suggests important differences between shifts of covert attention and preparation of eye movements. Finally, Chapter 6 investigated the mechanism driving the RDE. In particular it was assessed whether saccadic inhibition (Reingold & Stampe, 2002) is responsible for the increase in saccadic latency induced by remote distractors. Examination of the distributions of saccadic latencies at different distractor delays showed that each distractor produced a discrete dip in saccadic frequency, time-locked to distractor onset, conforming closely to the character of saccadic inhibition. It is concluded that saccadic inhibition underlies the remote distractor effect.