Les agrégats cellulaires constituent un modèle intermédiaire entre les cellules uniques et les tissues cellulaires et sont utilisés dans de nombreux domaines tels que l’ingénierie tissulaire et le criblage de médicaments in vitro. La création de tels agrégats cellulaires dont les propriétés et la taille seraient contrôlées nécessite cependant le développement de nouvelles approches ascendantes. Le travail présenté dans ce manuscrit vise à développer des microsystèmes pour la formation contrôlée d’agrégats de cellules sous flux via des champs électriques. Cette approche se base sur la diélectrophorèse (DEP), un phénomène induisant le déplacement des particules diélectriques lorsqu’elles sont placées dans un champ électrique non-uniforme. Un outil de calcul, MyDEP, a tout d’abord été développé afin d’être en mesure de prédire le comportement des cellules en suspension dans un certain milieu. Cet outil permet d’étudier la réponse diélectrique des particules et des cellules en fonction de la fréquence du champ. Il contient une base de données regroupant les propriétés diélectriques des cellules publiées dans la littérature afin d’aider tant les spécialistes que les utilisateurs néophytes à comprendre le comportement diélectrophorétique des particules et des cellules ainsi qu’à choisir les paramètres expérimentaux tels que la conductivité électrique du milieu et la fréquence du champ préalablement aux manipulations expérimentales en laboratoire. Différents designs pour le piégeage de cellules sont proposés avec les simulations, par la méthode des éléments finis en utilisant COMSOL Multiphysics, associées. Leur fabrication a nécessité le développement d’une méthode d’alignement reproductible, précise au micromètre, des microcanaux d’un polymère appelé le polydiméthylsiloxane (PDMS) avec des électrodes coplanaires en titane/platine déposées sur du verre via l’utilisation d’une aligneuse de masques conventionnelle. La méthode est basée sur l’utilisation d’un moule en silicium associé à un sarcophage en Poly(methyl methacrylate) (PMMA) afin de garantir le contrôle du parallélisme entre les parties supérieure et inférieure du PDMS moulé. Les puces contenant les différents designs de piégeage ainsi fabriquées ont été testées avec succès sur des cellules rénales embryonnaires humaines (HEK) à l’aide d’une installation expérimentale démontrant par la même la capacité des puces à créer des agrégats constitués d’un nombre contrôlé de cellules par diélectrophorèse. Les agrégats ainsi formés se sont avérés stables après 5 minutes de contact cellule à cellule sans qu’une séparation des cellules n’ait été observée. Le design d’un capteur par impédance a par ailleurs été proposé pour caractériser tant les cellules uniques que les agrégats cellulaires avant et après la chambre de piégeage. Celui-ci, associé au design de piégeage par DEP, a été testé expérimentalement avec succès pour détecter leur passage. / Cell aggregates are an intermediary model between single cells and cell tissues used in many applications such as tissue engineering and in vitro drug screening. The creation of cells aggregates of controlled size and properties requires the development of new bottom-up strategies. The work developed in this manuscript aims at presenting the development of microsystems for the electric force-driven controlled formation of cell aggregates under flow conditions. This approach is based on dielectrophoresis, a phenomenon that causes induced motion on dielectric particles placed in a non-uniform electric field. A computational tool, MyDEP, was first developed in order to predict the behavior of cells in a specific medium. It allows to study the dielectric response of particles and cells as a function of frequency. The software also includes a database gathering cell dielectric models available in the literature to help experienced users as well as neophytes to understand the dielectrophoretic behavior of particles and cells and to choose parameters such as electric conductivity of the medium and frequency before performing laboratory experiments. Different designs for cell trapping are proposed and simulated in 2D with FEM using COMSOL Multiphysics. Their fabrication implied the development of a reproducible method for μm precision alignment of microchannels in a polymer called polydimethylsiloxane (PDMS) with coplanar titanium/platinum electrodes deposited on glass, using a conventional mask aligner. It is based on the use of a silicon mold in combination with a Poly(methyl methacrylate) (PMMA) sarcophagus for precise control of the parallelism between top and bottom surfaces of molded PDMS. The trapping design based on coplanar electrodes was successfully tested experimentally on human embryonic kidney cells (HEK) with an automated setup. It proves its capability to create aggregates of a controlled number of cells with DEP. The cell aggregates proved to be stable (no disruption) after only 5 minutes of cell-cell contact. An impedance-based sensor design was proposed for characterizing single cells and cells aggregates before and after the trapping chamber. This sensor was successfully tested experimentally to detect particle passage in combination with the dielectrophoretic trapping design.

Les petits mammifères constituent les vertébrés responsables des dégâts les plus importants pour l'agriculture de l'Europe centrale. Dans les prairies de moyenne montagne, les populations de campagnol terrestre (Arvicola terrestris sherman) sont à l'origine de pullulations cycliques conséquentes depuis les années 70. En France, une des explications est que l'intensification de l'agriculture a conduit à l'ouverture des milieux agricoles et à la conversion de la majorité des terres en prairies toujours en herbe. Actuellement, le rôle de la structure et de la composition du paysage est établi aux échelles régionale et sectorielle mais on ne connaît pas le rôle des caractéristiques édaphiques des prairies sur les populations de A. terrestris à l'échelle parcellaire. L'objectif de ce travail de thèse était de déterminer, à l'échelle parcellaire, le rôle de la végétation des prairies, en relation avec le sol et le mode de conduite agricole, sur la dynamique des populations de A. terrestris. Dans des parcelles agricoles situées en Franche-Comté, différentes phases d'un cycle de population de A. terrestris ont été étudiées de 2001 à 2004 : basse densité, croissance, haute densité. Dans chaque parcelle d'étude, le suivi des populations de A. terrestris a été effectué par une méthode indiciaire d'estimation des densités relatives. Les populations de taupe (Talpa europaea) et de campagnol des champs (Microtus arvalis) ont également été prises en compte, en raison de leurs interactions possibles avec A. terrestris. Dans chaque parcelle, la végétation a été étudiée par ses caractéristiques structurelles (mesures de hauteur – compacité du couvert végétal) et fonctionnelles (fréquences des traits d'histoire de vie des espèces végétales). Les propriétés du sol ont été évaluées par les caractéristiques morphologiques (profondeur, texture, structure) et physico-chimiques (matière organique, pH, hydromorphie). Les données de pratiques agricoles (fauche, pâture, fertilisation, labour) ont été recueillies par le biais d'enquêtes auprès des exploitants agricoles des parcelles d'étude. Les principaux résultats montrent que les dynamiques de croissance des populations de A. terrestris sont favorisées par un régime agricole de production intensif, impliquant de nombreuses fauches et une forte fertilisation. Ce régime engendre une végétation à croissance rapide, caractérisée par une faible diversité spécifique et une forte valeur pastorale. Ponctuellement, en phase de haute densité, les populations de A. terrestris sont favorisées par un couvert végétal homogène, haut et dense et défavorisées par des pratiques telles que pâturage intensif et travail du sol. Le mode d'exploitation agricole influencerait les populations de A. terrestris en agissant sur la qualité et la disponibilité de la ressource nutritive végétale et sur la structure de l'habitat sol plante. De plus, à mode de conduite agricole constant, les caractéristiques pédologiques ne semblent pas exercer d'influence. Des résultats complémentaires indiquent que l'intensité de la colonisation des parcelles par A. terrestris est favorisée par les populations de T. europaea en phase de basse densité. En conclusion, notre étude montre qu'un seul facteur explicatif n'est pas suffisant mais que c'est bien la configuration d'un ensemble de variables qui explique la dynamique de populations de A. terrestris à l'échelle parcellaire. La prise en compte de cette régulation multifactorielle dans les programmes de contrôle des populations de A. terrestris pourra en améliorer l'efficacité à long terme. Des expérimentations à l'interface entre les domaines de la recherche et de l'application sont nécessaires pour parvenir à un compromis acceptable entre préconisation de pratiques agricoles défavorables aux pullulations de A. terrestris, remplissage des cahiers des charges des productions d'AOC et respect de l'environnement.

This work presents mainly two contributions to Description Logics (DLs) research by means of Formal Concept Analysis (FCA) methods: supporting bottom-up construction of DL knowledge bases, and completing DL knowledge bases. Its contribution to FCA research is on the computational complexity of computing generators of closed sets.

Ce travail de thèse porte sur l'organisation de nanoparticules sur des surfaces grâce à une approche originale basée sur le dépôt à faible énergie d'agrégats, préformés en phase gazeuse (approche Bottom-up), sur substrats de graphite HOPG, fonctionnalisés par des réseaux 2D de défauts créés par faisceau d'ions focalisés nano-FIB (approche Top-down). L'obtention de réseaux 2D d'amas d'agrégats est conditionnée par la diffusion des agrégats déposés et leur sensibilité aux défauts artificiels FIB. Le développement de cette approche passe tout d'abord par des simulations Monte-Carlo réalisées dans le cadre du modèle DDA (Dépôt-Diffusion-Agrégation). Ensuite, sa faisabilité expérimentale est testée avec succès en déposant des agrégats d'or. En particulier, cette étude montre la dépendance des propriétés morphologiques et structurales des défauts FIB en fonction de la dose d'ions. Par ailleurs, la sensibilité des agrégats aux défauts FIB, ainsi que la possibilité de contrôler la taille des amas, la période du réseau et sa géométrie sont analysées. Enfin, en se plaçant dans les conditions optimales permettant la meilleure organisation, notre approche est étendue aux agrégats magnétiques Co50Pt50, candidats potentiels au stockage d'information à ultra-haute densité. Une étude de l'influence du recuit sur les réseaux d'agrégats Co50Pt50 montre une amélioration de la qualité de l'organisation, et surtout une transition de phase des agrégats de la structure<br />A1 vers la structure L10.

Processkartläggning, som plattform för processbaserad verksamhetsutveckling, kan användas i hälso- och sjukvård för att kunna förstå en process och ge förutsättningar för förbättringar av den. Utgångspunkten var att det i litteraturen saknades en kartläggning av en vårdprocess som inkluderar sjukskrivningar, och sjukskrivningar ökar. Syftet var att förstå förutsättningarna för processbaserad verksamhetsutveckling gällande hälso- och sjukvårdens aktiviteter i primärvård för de patienter som söker vård vid förstämningssyndrom eller ångest/stress. Datainsamling gjordes i form av intervju samt processkartläggning av aktiviteter mellan sjukskrivning 1 och 2. Resultatet visade att berättelser med utgångspunkt i bra och dåliga erfarenheter av vårdprocessen kunde kopplas till framgångsfaktorer vad gäller förbättrad hälsa och återgång till arbete. De intervjuades roller, erfarenheter och syn på patientens behov gav upphov till olika förbättringsförslag gällande processen. Processkartläggningen visade på behov av en gemensam bild. Förslag till framtida processkartläggning gavs med utgångspunkt i resultatet. / Process mapping, as a prerequisite for process based organizational development, can be used in health care in order to understand the process and to provide possibilities of improving it. In the literature there was no mapping of the care process that includes sick leave, and sick leave increases. The purpose of the study was to understand the prerequisites for organizational development based on process mapping concerning primary health care activities for psychiatric diagnoses. Data collection was done by interviewing health professionals and by process mapping activities in the first period of sickness absence. The results showed that the stories based on good and bad experiences of the care process could be linked to success factors in terms of improved health and return to work. The informants different roles, experiences and perspective on the patient's needs gave rise to various suggestions for improvement of the process. Process mapping showed the need for a joint picture. Proposals based on the results, for future process mapping were given.

The field of high-energy physics has been living a very exciting period of its history with the Large Hadron Collider (LHC) at CERN collecting data. Indeed, this enormous machine able to collide protons at a center of mass energy of 14 TeV promises to unveil the mystery around the physics at such energy scales. From the physicists side, the expectations are very strong as it isnowadays a certitude that the Standard Model of particle physics is incomplete and should, in fact, be interpreted as the effective theory of a more fundamental one. Unfortunately, the 7 and 8 TeV runs of the LHC did not provide any sign of new physics yet but there has been at least one major discovery in 2010, namely the discovery of a scalar particle with a mass of 125 GeV and whichproperties are very close to those of the Standard Model Higgs boson. Since then, many questions have come up as we now want to understand if it really is the Standard Model Higgs boson or if it exhibits any deviations. It is in this peculiar context that my research work was carried. In a first project, we, my supervisors, our collaborator and I, have wanted to explore thephenomenology associated with the neutralinos and charginos sector of the left-right symmetric supersymmetric model. Such an analysis can be motivated by several reasons such as the fact that the supersymmetric nature of these models provides a natural explanation for the infamous hierarchy problem, implies the unification of the gauge coupling constants at very high energy and provides a natural candidate for dark matter. In addition to these nice features, the left-right symmetry introduces a natural framework for explaining the smallness of neutrino masses but also helps in addressing several other unresolved issues in the Standard Model framework. Only focusing on the lightest charginos and neutralinos decaying into one or more light leptons, we have shown in our study that these models can be easily discovered in multi-leptonic final states as theylead to signatures very different from those induced by the Standard Model or its supersymmetric version.[...]

Worldwide tourism has become one of the largest and fastest growing industries. Specifically in the South African context, this growth has been confirmed in recent statistics. However, the growth in the tourism industry does not occur without challenges. It brings both benefits and costs to the residents of a host community, consequently generating both positive and negative tourism impacts. Further, it is recognised that once a community becomes a tourism destination, the lives of the residents are influenced by that particular development; thus effecting their Quality of Life (QoL). Only minimal research has, however, been conducted to determine the influence of the perceived impacts of tourism on residents’ QoL, especially in the South African context. A number of theoretical frameworks have been developed in tourism to signify how the perception of or reactions towards tourism of residents in a host community are influenced at any particular stage of development. Pertaining to QoL, various theoretical models have also been created to describe the functioning of the construct. Although theoretical frameworks have been developed that are distinct to tourism and QoL; to date an integrated approach does not exist that explores the influence of tourism on residents’ QoL. In addition to the lack of an integrated approach in literature, the permanency of tourism products too have not yet been examined in literature. Further, permanency has not been examined in order to determine the influence of tourism impacts on residents’ QoL in selected towns, one being a permanent tourism product (PTP) and the other a nonpermanent tourism product (N-PTP). From the above, it can be seen that three theoretical and practical issues exist: (1) only a modest amount of research has been done to determine the influence of tourism impacts on residents’ QoL; (2) an integrated approach does not exist signifying the relationship between tourism impacts and QoL and; (3) permanency as a differentiation factor has not been investigated in host communities. By addressing these issues, a significant contribution will be made to literature, together with the ensuing practical contributions. Therefore, the main goal of the study was to develop a model to indicate the influence of perceived impacts of tourism on residents’ QoL in selected towns; these having specific differentiation made between a PTP and N-PTP. In order to achieve the goal of the study, five objectives were formulated: The first objective was to analyse theoretical frameworks of tourism and QoL and to identify a particular theoretical framework for the study. Specifically, the Social Exchange Theory (SET) was selected from the theoretical frameworks of tourism, while the Bottom-up Spillover theory was designated as it is peculiar to QoL frameworks. Therefore, the derived theoretical framework indicated that an ‘exchange’ process occurs between tourism development and the residents of the host community. More specifically, social exchange arises between the perceived impacts of tourism and life domains in order to establish the QoL of residents in host communities. The second objective was to analyse tourism both as an industry and product in a host community through a review of existing literature. From the literature review, it can be seen that tourism is a growing industry and product, not only internationally but also in the South African context. Permanency as a characteristic was explored comprehensively to define a tourism product while maintaining the differentiation between a PTP and N-PTP. Residents of a host community are noted as important roleplayers in the tourism industry as tourism impacts affect them in PTP and in N-PTP. This importance is emphasised as residents of a host community: (1) influence the tourism experience; (2) determine the attractiveness of a destination and; (3) control the sustainability of tourism in a host community. The third objective was to analyse QoL and its relation to the residents of a host community, once more, through a literature review. From the review, it was observed that QoL has different definitions and views, some more intricate than others. For the purpose of the study, it was determined that QoL can be described appropriately through the Bottom-up Spillover theory. Therefore, QoL is determined through the collaboration of various life domains that, further, may be either objective or subjective in nature. When examining the relationship between tourism development and QoL, it was established that tourism, through tourism products, produces effects that will influence various life domains, consequently determining the QoL of residents in a host community. As with tourism impacts, the QoL of the host community’s residents will subsequently: (1) influence the tourism experience; (2) determine the attractiveness of a destination and; (3) ensure the sustainability of tourism in a community. The fourth objective was to analyse the influence of the economic, environmental, social and cultural impacts of tourism on residents’ QoL and to differentiate between a PTP and N-PTP by using an empirical study. Having in mind that the main goal of the study was to develop a model, Confirmatory Factor Analysis (CFA) and Structural Equation Modelling were conducted on the data. The models, constructed separately for tourism impacts and QoL, were subsequently integrated to determine the influence of the perceived impacts of tourism on residents’ QoL. The model with good model fit statistics and supportive of underlying theory was thereafter accepted for further analysis in order to attain comprehensively the main goal of the study. Thereafter, model development tested permanency of tourism products by specifically determining the influence of perceived impacts of tourism on residents’ QoL in selected towns (PTP and N-PTP). From the latter exercise, no practically significant differences were found between a PTP and N-PTP. Therefore, the model constructed as Stage 3 was accepted as the final model of the study and was given the title of Root’s model of Community TourQoL (CTQ). Specifically, the model signified that positive economic, environmental, social and cultural impacts influence residents’ QoL, while negative environmental and social impacts do not influence residents’ QoL in host community. Furthermore, the model showed that no differences were found between a PTP and N-PTP regarding the influence of perceived impacts of tourism on residents’ QoL. The fifth and final objective was to draw conclusions, indicate contributions, formulate recommendations and present limitations peculiar to the study. The greatest significance of the study is seen in the practical contributions of the study, specifically, the development of Root’s model of Community TourQoL (CTQ). Community and tourism planners and/management can implement the model in both PTP and N-PTP to enhance the positive impacts of tourism; while minimising negative impacts, in order to improve residents’ QoL. / Thesis (PhD (Tourism Management))--North-West University, Potchefstroom Campus, 2013.

Worldwide tourism has become one of the largest and fastest growing industries. Specifically in the South African context, this growth has been confirmed in recent statistics. However, the growth in the tourism industry does not occur without challenges. It brings both benefits and costs to the residents of a host community, consequently generating both positive and negative tourism impacts. Further, it is recognised that once a community becomes a tourism destination, the lives of the residents are influenced by that particular development; thus effecting their Quality of Life (QoL). Only minimal research has, however, been conducted to determine the influence of the perceived impacts of tourism on residents’ QoL, especially in the South African context. A number of theoretical frameworks have been developed in tourism to signify how the perception of or reactions towards tourism of residents in a host community are influenced at any particular stage of development. Pertaining to QoL, various theoretical models have also been created to describe the functioning of the construct. Although theoretical frameworks have been developed that are distinct to tourism and QoL; to date an integrated approach does not exist that explores the influence of tourism on residents’ QoL. In addition to the lack of an integrated approach in literature, the permanency of tourism products too have not yet been examined in literature. Further, permanency has not been examined in order to determine the influence of tourism impacts on residents’ QoL in selected towns, one being a permanent tourism product (PTP) and the other a nonpermanent tourism product (N-PTP). From the above, it can be seen that three theoretical and practical issues exist: (1) only a modest amount of research has been done to determine the influence of tourism impacts on residents’ QoL; (2) an integrated approach does not exist signifying the relationship between tourism impacts and QoL and; (3) permanency as a differentiation factor has not been investigated in host communities. By addressing these issues, a significant contribution will be made to literature, together with the ensuing practical contributions. Therefore, the main goal of the study was to develop a model to indicate the influence of perceived impacts of tourism on residents’ QoL in selected towns; these having specific differentiation made between a PTP and N-PTP. In order to achieve the goal of the study, five objectives were formulated: The first objective was to analyse theoretical frameworks of tourism and QoL and to identify a particular theoretical framework for the study. Specifically, the Social Exchange Theory (SET) was selected from the theoretical frameworks of tourism, while the Bottom-up Spillover theory was designated as it is peculiar to QoL frameworks. Therefore, the derived theoretical framework indicated that an ‘exchange’ process occurs between tourism development and the residents of the host community. More specifically, social exchange arises between the perceived impacts of tourism and life domains in order to establish the QoL of residents in host communities. The second objective was to analyse tourism both as an industry and product in a host community through a review of existing literature. From the literature review, it can be seen that tourism is a growing industry and product, not only internationally but also in the South African context. Permanency as a characteristic was explored comprehensively to define a tourism product while maintaining the differentiation between a PTP and N-PTP. Residents of a host community are noted as important roleplayers in the tourism industry as tourism impacts affect them in PTP and in N-PTP. This importance is emphasised as residents of a host community: (1) influence the tourism experience; (2) determine the attractiveness of a destination and; (3) control the sustainability of tourism in a host community. The third objective was to analyse QoL and its relation to the residents of a host community, once more, through a literature review. From the review, it was observed that QoL has different definitions and views, some more intricate than others. For the purpose of the study, it was determined that QoL can be described appropriately through the Bottom-up Spillover theory. Therefore, QoL is determined through the collaboration of various life domains that, further, may be either objective or subjective in nature. When examining the relationship between tourism development and QoL, it was established that tourism, through tourism products, produces effects that will influence various life domains, consequently determining the QoL of residents in a host community. As with tourism impacts, the QoL of the host community’s residents will subsequently: (1) influence the tourism experience; (2) determine the attractiveness of a destination and; (3) ensure the sustainability of tourism in a community. The fourth objective was to analyse the influence of the economic, environmental, social and cultural impacts of tourism on residents’ QoL and to differentiate between a PTP and N-PTP by using an empirical study. Having in mind that the main goal of the study was to develop a model, Confirmatory Factor Analysis (CFA) and Structural Equation Modelling were conducted on the data. The models, constructed separately for tourism impacts and QoL, were subsequently integrated to determine the influence of the perceived impacts of tourism on residents’ QoL. The model with good model fit statistics and supportive of underlying theory was thereafter accepted for further analysis in order to attain comprehensively the main goal of the study. Thereafter, model development tested permanency of tourism products by specifically determining the influence of perceived impacts of tourism on residents’ QoL in selected towns (PTP and N-PTP). From the latter exercise, no practically significant differences were found between a PTP and N-PTP. Therefore, the model constructed as Stage 3 was accepted as the final model of the study and was given the title of Root’s model of Community TourQoL (CTQ). Specifically, the model signified that positive economic, environmental, social and cultural impacts influence residents’ QoL, while negative environmental and social impacts do not influence residents’ QoL in host community. Furthermore, the model showed that no differences were found between a PTP and N-PTP regarding the influence of perceived impacts of tourism on residents’ QoL. The fifth and final objective was to draw conclusions, indicate contributions, formulate recommendations and present limitations peculiar to the study. The greatest significance of the study is seen in the practical contributions of the study, specifically, the development of Root’s model of Community TourQoL (CTQ). Community and tourism planners and/management can implement the model in both PTP and N-PTP to enhance the positive impacts of tourism; while minimising negative impacts, in order to improve residents’ QoL. / Thesis (PhD (Tourism Management))--North-West University, Potchefstroom Campus, 2013.

The reduction of the impact of energy consumption is a priority issue and a major challenge that concerns every country in the world. This is a complex task that needs to be tackled from several angles in the search for areas where optimizations and savings can be made. In Sweden an electricity meter reading reform was fully implemented by 1st July 2009, including 5.2 million customers, and this created new set of circumstances in the Swedish electricity market. The main purpose of this thesis work has been to investigate the possibilities of increasing the use of remote meter readings. Two research questions have been: “How can the electricity market benefit from remote collected meter readings?” and “Where do barriers appear when utilizing meter readings?”. The work started in 2000/2001 to study Internet based applications that visualize electricity consumption patterns. Over these years the daily internet users have increased from approximately 40 % to 73 % and new markets for web-based applications have evolved. These solutions can be important in the forthcoming years as energy portals that hold new energy services. Experiences from new installations indicate that at least interested customers do submit information concerning building and household properties through internet. Still, it is challenging to enable the majority of customers to take part in these new solutions. It may therefore be important to remind customers on a regular basis in order maintain the frequency using the application and to make it habitual. Further the introduction of demand-based pricing allows electricity distribution utilities to achieve a stronger correlation between peak loads in the distribution network area and their revenues.

Perceptual rivalry refers to visual phenomena that are characterised by alternations between different percepts, despite an unchanging sensory input. Two common types of perceptual rivalry are (i) reversible figures — two-dimensional stable images that when viewed, are perceived to switch between different interpretations, and (ii) binocular rivalry — the alternations in image dominance resulting from the presentation of conflicting stimuli, one to each eye. Several investigators have suggested that these rivalling phenomena are mediated by similar neural mechanisms. Such a view, however, has not only been inadequately substantiated, but has also yet to be assessed in the context of a directly testable neurophysiological model. Miller and Pettigrew have proposed a novel, high-level interhemispheric switch (IHS) explanatory model of binocular rivalry. This model conceptualises the perceptual alternations as being mediated by alternations between one hemisphere’s selected image and the other hemisphere’s selected (rival) image. To assess their hypothesis, caloric vestibular stimulation (CVS) was used. CVS is a simple, inexpensive, and non-invasive brain stimulation technique that unilaterally activates high-level attentional areas. In accordance with the IHS model, CVS was found to significantly affect predominance (the duration that one image is perceived relative to the other, within a given viewing period) during conventional binocular rivalry with horizontal/vertical gratings and with orthogonal oblique gratings. The present thesis therefore aims, through the use of CVS, to extend this IHS model of binocular rivalry to reversible-figure alternations and propose a general IHS model of perceptual rivalry. Chapter 1 provides a detailed literature review of the field within the context of comparing both perceptual rivalries. In Chapter 2, investigations are presented on two different reversible figures — the perspective-reversing Necker cube and the figure–ground reversing Rubin’s vase–faces illusion. In these experiments, CVS was found to significantly change observers’ predominance compared to their baseline predominance. These results demonstrate that interhemispheric switching also mediates the alternations of these visual phenomena, in addition to binocular rivalry, thereby extending the IHS model to one of perceptual rivalry in general. Moreover, the findings are interpreted in a cognitive neuroscience context, including a novel proposal of a forebrain framework for the IHS model. Chapter 3 presents CVS experiments that address the issue of percept–to–hemisphere selection and the reproducibility of CVS effects, following Miller’s initial work on two types of conventional binocular rivalry. In planned analyses, significant predominance changes were not found in horizontal/vertical rivalry, oblique rivalry and Necker-cube rivalry. In post-hoc analyses that accounted for study-design differences between Miller’s original experiments and the present experiment, CVS was again not shown to induce significant predominance changes in any of the rivalry types. Assessment of directional predominance changes following CVS appeared to suggest an arbitrary selection of percept–to–hemisphere in all rivalry types, although no firm conclusions could be drawn from the obtained data on this issue. Nevertheless, the experiments further extend upon Miller’s earlier work by examining the inter- and intra-individual reproducibility of CVS-induced effects on predominance. Such reproducibility was found to be low and potential reasons for this are discussed. The experiments in Chapter 4 examine a type of binocular rivalry in which dichoptic presentation of Díaz-Caneja stimuli yields rivalry among four different stable images: half-field rivalry between the images presented to the eyes, and coherence rivalry in which aspects of each eye’s presented image are perceptually regrouped into rivalling coherent images. Each of these rivalries was found to occur for about half the given viewing time. Furthermore, CVS significantly shifted the predominance of perceived coherent images (coherence rivalry) but not half-field images (eye rivalry). This finding suggests that coherence rivalry (like conventional rivalry according to previous experiments) is mediated by interhemispheric switching at a high level, while eye rivalry is mediated by intrahemispheric mechanisms, most likely at a low level. In addition, it is proposed that Díaz-Caneja stimuli induce ‘meta-rivalry’ whereby these discrete high- and low-level competitive processes themselves rival for visual consciousness. The current thesis thus presents a novel meta-rivalry model of multistable binocular rivalry. It also presents the first direct evidence that interhemispheric switching mediates reversible-figure alternations, thereby supporting a generalised IHS model of perceptual rivalry. It is argued that both models provide a parsimonious exploratory framework within which specific predictions can be made and readily tested. Finally, the findings of all experiments in the current thesis are summarised.