O presente estudo teve por objetivo investigar a dinâmica temporal da percepção de tamanho de objetos inseridos em gradientes de textura, provenientes de desenho gerado computacionalmente (gradiente de perspectiva) e de fotografia com elementos naturais (gradiente fotografado). Além disso, verificou-se a ocorrência e padrão dos movimentos oculares nestas condições. Para isso, foram realizados 2 experimentos. No primeiro experimento, dois círculos negros eram apresentados no meridiano vertical e a tarefa dos 96 participantes foi indicar em qual parte do campo visual, superior ou inferior, foi apresentado o maior círculo. Usando o método das escadas duplas, estes círculos eram apresentados brevemente (50, 100, 150 ou 200 ms) em três condições de fundos de tela (sem textura, gradiente de perspectiva ou gradiente fotografado). Foram calculados a inclinação da função psicométrica e o ponto de igualdade subjetivo (PIS) como medidas da sensibilidade discriminativa e da distorção perceptiva, respectivamente. Os resultados mostraram que os participantes discriminaram melhor o tamanho dos estímulos à medida que o tempo de exposição aumentava, independentemente do gradiente de textura. A análise do PIS revelou que há uma forte distorção do tamanho aos 100 ms para o gradiente de perspectiva e aos 150 ms para o gradiente fotografado. No segundo experimento, 24 participantes realizaram uma tarefa semelhante ao do primeiro experimento e utilizou-se um eye tracker para registrar o movimento ocular. Os resultados mostraram que, em apresentações de 150 e 200 ms, os movimentos oculares ocorreram em menos de 10% das tentativas em todos os fundos de tela. Isto indica que a redução das distorções de tamanho após os 100 ms observada no primeiro experimento não é explicada completamente pela alocação da atenção. Tomados em conjunto, estes resultados sugerem que o processamento e integração das informações de tamanho e profundidade são mediados principalmente por mecanismos bottom-up. Ademais, em uma condição de menor restrição temporal (1500 ms), a presença de informações de profundidade afetou a dimensão espacial das fixações e sacadas, mas não a dimensão temporal. Os participantes olharam preferencialmente para o estímulo apresentado no campo visual superior, o que indica que a atenção foi alocada às posições de maior profundidade. Os resultados também indicaram que os estímulos maiores capturaram tanto a atenção transitória quanto a atenção sustentada. Assim, este estudo permitiu um maior conhecimento sobre os mecanismos perceptivos e atentivos envolvidos no processamento das informações de tamanho e de profundidade. / This study aimed to investigate the temporal dynamics of object size perception under texture gradients from line-drawing (perspective gradient) and photograph with natural elements (photographed gradient). Additionally, it was analyzed the occurrence and the pattern of eye movements in these conditions. For this, we carried out 2 experiments. In the first experiment, two black circles were displayed in the vertical meridian and 96 participants reported whether the bigger one was presented at the lower or upper visual field. By using double staircase psychophysics method, these circles were briefly presented (50, 100, 150 or 200 ms) in three background conditions (no texture, perspective gradient or photographed gradient). The slope of the psychometric function and the points of subjectivity equality (PSE) were calculated and used as discrimination sensitivity and size distortion measures, respectively. The results showed a greater sensitivity to size discrimination as exposure time increased, regardless the texture gradient. The analysis of PSE indicated greater size distortions in perspective gradient at 100 ms and in photographed gradient at 150 ms. In the second experiment, 24 participants performed a task similar to that in Experiment 1 while an eye tracker recorded their eye-movements. The results showed that, at 150 and 200 ms, eye movements occurred in less than 10% of trials in all backgrounds. It indicates that the size distortion reduction after 100 ms observed in the first experiment cannot be fully explained by attention allocation. Taken together, these results suggest that the process and integration of size and depth information are mainly mediated by bottom-up mechanism. Moreover, in a less time constrain condition (1500 ms), depth cues affected the spatial measures of fixations and saccades, but not the temporal ones. The participants looked more frequently at the stimulus on the upper visual field, indicating that attention has been allocated to positions of greater depth. The results also indicated that large stimulus capture both transient and sustained attention. Thus, this study provides a better understanding of perceptual and attentive mechanisms involved in size and depth process.

O presente estudo teve por objetivo investigar a dinâmica temporal da percepção de tamanho de objetos inseridos em gradientes de textura, provenientes de desenho gerado computacionalmente (gradiente de perspectiva) e de fotografia com elementos naturais (gradiente fotografado). Além disso, verificou-se a ocorrência e padrão dos movimentos oculares nestas condições. Para isso, foram realizados 2 experimentos. No primeiro experimento, dois círculos negros eram apresentados no meridiano vertical e a tarefa dos 96 participantes foi indicar em qual parte do campo visual, superior ou inferior, foi apresentado o maior círculo. Usando o método das escadas duplas, estes círculos eram apresentados brevemente (50, 100, 150 ou 200 ms) em três condições de fundos de tela (sem textura, gradiente de perspectiva ou gradiente fotografado). Foram calculados a inclinação da função psicométrica e o ponto de igualdade subjetivo (PIS) como medidas da sensibilidade discriminativa e da distorção perceptiva, respectivamente. Os resultados mostraram que os participantes discriminaram melhor o tamanho dos estímulos à medida que o tempo de exposição aumentava, independentemente do gradiente de textura. A análise do PIS revelou que há uma forte distorção do tamanho aos 100 ms para o gradiente de perspectiva e aos 150 ms para o gradiente fotografado. No segundo experimento, 24 participantes realizaram uma tarefa semelhante ao do primeiro experimento e utilizou-se um eye tracker para registrar o movimento ocular. Os resultados mostraram que, em apresentações de 150 e 200 ms, os movimentos oculares ocorreram em menos de 10% das tentativas em todos os fundos de tela. Isto indica que a redução das distorções de tamanho após os 100 ms observada no primeiro experimento não é explicada completamente pela alocação da atenção. Tomados em conjunto, estes resultados sugerem que o processamento e integração das informações de tamanho e profundidade são mediados principalmente por mecanismos bottom-up. Ademais, em uma condição de menor restrição temporal (1500 ms), a presença de informações de profundidade afetou a dimensão espacial das fixações e sacadas, mas não a dimensão temporal. Os participantes olharam preferencialmente para o estímulo apresentado no campo visual superior, o que indica que a atenção foi alocada às posições de maior profundidade. Os resultados também indicaram que os estímulos maiores capturaram tanto a atenção transitória quanto a atenção sustentada. Assim, este estudo permitiu um maior conhecimento sobre os mecanismos perceptivos e atentivos envolvidos no processamento das informações de tamanho e de profundidade. / This study aimed to investigate the temporal dynamics of object size perception under texture gradients from line-drawing (perspective gradient) and photograph with natural elements (photographed gradient). Additionally, it was analyzed the occurrence and the pattern of eye movements in these conditions. For this, we carried out 2 experiments. In the first experiment, two black circles were displayed in the vertical meridian and 96 participants reported whether the bigger one was presented at the lower or upper visual field. By using double staircase psychophysics method, these circles were briefly presented (50, 100, 150 or 200 ms) in three background conditions (no texture, perspective gradient or photographed gradient). The slope of the psychometric function and the points of subjectivity equality (PSE) were calculated and used as discrimination sensitivity and size distortion measures, respectively. The results showed a greater sensitivity to size discrimination as exposure time increased, regardless the texture gradient. The analysis of PSE indicated greater size distortions in perspective gradient at 100 ms and in photographed gradient at 150 ms. In the second experiment, 24 participants performed a task similar to that in Experiment 1 while an eye tracker recorded their eye-movements. The results showed that, at 150 and 200 ms, eye movements occurred in less than 10% of trials in all backgrounds. It indicates that the size distortion reduction after 100 ms observed in the first experiment cannot be fully explained by attention allocation. Taken together, these results suggest that the process and integration of size and depth information are mainly mediated by bottom-up mechanism. Moreover, in a less time constrain condition (1500 ms), depth cues affected the spatial measures of fixations and saccades, but not the temporal ones. The participants looked more frequently at the stimulus on the upper visual field, indicating that attention has been allocated to positions of greater depth. The results also indicated that large stimulus capture both transient and sustained attention. Thus, this study provides a better understanding of perceptual and attentive mechanisms involved in size and depth process.

Les savanes sont des écosystèmes complexes pilotées par plusieurs mécanismes ascendant (ex: les nutriments du sol ou pluviométrie) ou descendant (ex: feu ou herbivorie), mais l'importance relative de ces mécanismes reste largement débattue. En particulier, le rôle des herbivores brouteurs (browsers) reste mal compris en tant que source de perturbation, et donc de force de pression descendante influant sur la dynamique des savanes. Dans cette étude, deux approches ont été développées pour aborder le rôle des perturbations dans la dynamique des savanes. Dans un première partie, j'ai utilisé une approche comparative inter-site pour explorer les réponses des communautés de plantes, et des principaux traits de ces plantes associés aux feuilles, branches, architecture et défense, aux variations de quatre facteurs : les nutriments dans le sol, la pluviométrie, la pression d'herbivorie et l'intensité du feu. Seize sites de savane, en Afrique du Sud et au Zimbabwe, ont été sélectionnés sur des gradients de chacun de ces facteurs. Les espèces ligneuses dominantes (>80 % de la biomasse) sur chaque site ont été identifiées et échantillonnées, afin de mesurer les traits des feuilles et des branches associés à l'appétence, architecture, ainsi qu'aux défenses physiques et chimiques de ces plantes. Des mesures ont également été faites pour estimer les effets des meso-brouteurs et mega-brouteurs. Des transects ont permis d'estimer la fréquence et l'intensité du feu sur chaque site, et l'effet sur les plantes. En préambule à l'analyse, et devant le manque de protocole standard pour estimer la fertilité des sols dans la littérature écologique, je propose une méthode et un échantillonnage afin de définir de manière robuste la fertilité des sols sur chaque site. Dans cette partie inter-site, huit traits principaux ont été comparés sur le gradient de qualité de sol et de pluviométrie, et bien que quelques relations statistiques existent entre les traits des feuilles, le sol et la pluviométrie, ces relations sont très faibles comparées à celle trouvées dans les méta analyses inter-biomes publiées dans la littérature. Cependant, ces approches interbiome sont dominées par des sites tempérés qui ont des niveaux de perturbations bien inférieurs à ceux des savanes africaines. L'évaluation des effets des meso-brouteurs et mega-brouteurs le long des gradients de sol et de pluviométrie sur vingt traits associés aux défenses structurelles et chimiques des plantes montre que les défenses structurelles sont plus corrélées aux caractéristiques du sol que les défenses chimiques, mais que seules les défenses structurelles sont fortement corrélées à l'impact par les brouteurs. Le niveau d'utilisation des plantes par les mesobrouteurs apparaît plus prévisible en fonction des traits des plantes que celui par les mégabrouteurs. Dans une deuxième partie présentent des résultats de deux études basées sur des expériences d'exclos. Dans le parc national de Kruger, la composition de la communauté, l'abondance et la démographie des ligneux dominants ont été estimées à l'intérieur et à l'extérieur de trois exclos de 40 ans, et les brouteurs apparaissent comme ayant un impact significatif sur la distribution, la densité et la structure des populations des espèces arbustives et arborées ayant des traits préférés : forte concentration en azote foliaire et faible teneur en défenses chimiques. L'interaction entre les effets des brouteurs et du feu semble aussi affecter le recrutement des juvéniles ligneux dans les grandes classes de taille. Dans le parc de Hluhluwe-iMfolozi, cinq exclos ont été utilisé pour tester l'effet des brouteurs sur l'architecture, la croissance, les défenses chimiques et structurelles des jeunes individus de sept espèces d'acacia. Des différences nettes apparaissent entre les espèces d'acacia de savane semi-aride et plus humide dans les traits associés à l'appétence, l'architecture et les défenses … [etc] / Savannas are complex ecosystems affected by several bottom-up (e.g. soil nutrient availability and rainfall) and top-down (e.g. fire and herbivory) drivers. However, the relative importance of bottom-up vs. top-down drivers in influencing savanna dynamics is still widely debated. Within the top-down (disturbance) category of drivers, the role of mammal browsers in particular in driving savanna functioning is still not well understood. Two approaches were adopted to determine the role of disturbance in savannas. Firstly, by using a comparative approach, I attempted to address the so-called ‘savanna problem’ by investigating how savanna woody plant community compositions and key plant traits relating to the leaves, stems, architecture, and defence are influenced by soil nutrient status, rainfall, fire and browsing. Sixteen sites were selected along gradients of these four drivers from savanna parks throughout South Africa and Zimbabwe. The dominant woody species (species that accounted for >80% of standing biomass) at each site were identified and sampled for the key leaf and stem traits relating to plant functioning, palatability, architecture, physical and chemical defences. Measurements were undertaken for each species in order to determine both meso-browser and mega browser impact. Transects were undertaken in order to determine the relative abundance and the effects of fire on each species at each site. Due to the current lack of standardized soil sampling protocols in the ecological literature, and uncertainty around the definition of what denotes a fertile or infertile soil, I propose a number of standardized protocols and sampled according to these established protocols in order to accurately determine the soil nutrient status at each site. Following this, the relationships between climatic variables and soil nutrients with both species means and community weighted means for eight key leaf traits were explored. Although some significant relationships were found between savanna leaf traits of woody plants, climate, soil nutrients and their interactions, these tended to be weaker than those found in meta-analyses. These broad-scale studies usually include sites from many biome types, many of which are from temperate regions where inherent levels of disturbance are typically much lower than in African savannas. The high levels of disturbance typically found in African savannas are thought to partially account for the high within site variability found in leaf traits and the weak relationships found between leaf traits, soil nutrients and rainfall. To assess the importance of resources vs. disturbance in savannas functioning, the effects of soil nutrients, rainfall, fire and both meso-browser and mega-browser impact on twenty savanna woody plant traits relating to plant palatability, chemical and structural defences were explored. Structural defences were found to be more strongly correlated with soil characteristics than chemical defences, while browser impact was found to be strongly correlated with structural defences but not with chemical defences. Actual browser utilisation tended to be more predictable for meso-browsers than mega-browsers. Secondly using an experimental approach, two sets of herbivore exclosures were utilized to directly test how mammal browsers influenced woody species distributions, abundance, population structure and plant traits relating to palatability and defence. The effects of three longterm herbivore exclosures in the Kruger National Park on savanna woody plant community compositions, population demographics and densities were determined. Browsers were found to have significant impacts on species distributions, densities and population structures by actively selecting for species with favourable traits, particularly higher leaf N. An interaction between browsers and fire which limited the recruitment of seedlings and saplings into larger size classes was also demonstrated… [etc]

<p>In contrast to effortful cognitive functions, emotional functioning may remain stable or even be enhanced in older adults. It is unclear how affective functions in aging correspond to subjective experiences and physiological changes. In <b>Study I</b>, ratings of emotional intensity and neural activity to facial expressions using functional magnetic resonance imaging (fMRI) were analyzed in younger and older adults. Negative expressions resulted in increased neural activity in the right amygdala and hippocampus in younger adults, and increased activation in the right insular cortex in older adults. There were no age differences in subjective ratings. In <b>Study II</b>, subjective ratings of, and skin conductance response (SCR) to, neutral and negative pictures were studied. The ratings of negative pictures were higher for older adults compared to younger adults. SCRs increased in both age groups for the negative pictures, but magnitude of SCRs was significantly larger in younger adults. Finally, in <b>Study III</b>, emotional memory after a one-year retention interval was tested. The memory performance of both age groups was higher in response to negative pictures compared to neutral ones, although the performance was generally higher for younger adults. SCR at encoding was the better arousal predictor for memory, but only in younger adults. The results indicate age-related changes in affective processing. Age differences may involve a gradual shift from bottom-up processes, to more top-down processes. The results are discussed in a wider lifespan perspective taking into consideration the accumulated life experience of older adults.</p>

In contrast to effortful cognitive functions, emotional functioning may remain stable or even be enhanced in older adults. It is unclear how affective functions in aging correspond to subjective experiences and physiological changes. In Study I, ratings of emotional intensity and neural activity to facial expressions using functional magnetic resonance imaging (fMRI) were analyzed in younger and older adults. Negative expressions resulted in increased neural activity in the right amygdala and hippocampus in younger adults, and increased activation in the right insular cortex in older adults. There were no age differences in subjective ratings. In Study II, subjective ratings of, and skin conductance response (SCR) to, neutral and negative pictures were studied. The ratings of negative pictures were higher for older adults compared to younger adults. SCRs increased in both age groups for the negative pictures, but magnitude of SCRs was significantly larger in younger adults. Finally, in Study III, emotional memory after a one-year retention interval was tested. The memory performance of both age groups was higher in response to negative pictures compared to neutral ones, although the performance was generally higher for younger adults. SCR at encoding was the better arousal predictor for memory, but only in younger adults. The results indicate age-related changes in affective processing. Age differences may involve a gradual shift from bottom-up processes, to more top-down processes. The results are discussed in a wider lifespan perspective taking into consideration the accumulated life experience of older adults.

This thesis investigates policy formulation and implementation processes in Zambia. A number of issues emerge with respect to the weaknesses of the system and how policy decisions worsened Zambia's economic performance instead of improving it. The Kaunda era policies of nationalization had an adverse impact on productivity of industries as well as affecting the resource flow from donors and business houses. On the other hand President Chiluba's reforms in the 1990s have had both positive and negative impacts on the people of Zambia. The rapid privatization and liberalization affected employment levels thereby worsening the poverty levels. Further, the liberalization brought in stiff competition from other countries forcing most manufacturing companies to close down. The policy environment based on the Bretton Woods Institutions seems not to be working as result of not taking into account the local Zambian situation. On the other hand, there were positive macroeconomic developments such as growth in GDP, lowering of inflation and stabilizing of exchange rates as from 1996. This has however not improved the living standards of the people. In Zambia, the shifts back and forth between strong and weak planning institutions have negatively affected policy development and implementation. There has been uncoordinated policy development; as a result, some policies in the major sectors are contradictory while in other cases policies are not linked to the resource envelope, making them un-implementable. Secondly, the institutional framework for policy development is not effective. There is generally lack of coordination among ministries, provinces and other stakeholders in planning, implementation and monitoring and evaluation of development programmes. This thesis urges that the improving planning capacities at the national, provincial and district levels should improve the processes of policy development and implementation in Zambia, which will in turn help to reduce poverty. Further, the districts should be the centre for the bottom-up process. In order to carryout this responsibility, efforts should be made to improve their capacities. As for the top-down process, the Sector Advisory Groups should continue to participate in the planning, monitoring and evaluation so as to contribute to policy formulation and implementation. These should be coordinated by the National Development Coordinating Committee (NDCC) through a Planning Bureau. / Development Studies / D. Litt. et Phil. (Development Studies)

Increasing involvement with students at the University of Namibia has indicated their overall difficulty with comprehending and recalling information from oral content lectures. It has also been observed that in general very little attention is given to the development of listening skills in L2 ESP and EAP courses. For this study, I conducted a quasi-experiment to determine whether the recognition and interpretation of discourse markers will enhance students' listening comprehension in academic lectures. Students were tested to determine their comprehension of content information in a video-taped lecture. Qualitative data were collected by means of a questionnaire. After an intervention period of eight weeks, where the experimental group received strategy training in the recognition and interpretation of discourse markers in spoken texts, both groups were again tested. Their results were statistically compared. I also looked at related findings of other researchers. Finally, aspects for possible future research will also be considered. / English Studies / MA - (Specialisation in TESOL)

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.

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.

Increasing involvement with students at the University of Namibia has indicated their overall difficulty with comprehending and recalling information from oral content lectures. It has also been observed that in general very little attention is given to the development of listening skills in L2 ESP and EAP courses. For this study, I conducted a quasi-experiment to determine whether the recognition and interpretation of discourse markers will enhance students' listening comprehension in academic lectures. Students were tested to determine their comprehension of content information in a video-taped lecture. Qualitative data were collected by means of a questionnaire. After an intervention period of eight weeks, where the experimental group received strategy training in the recognition and interpretation of discourse markers in spoken texts, both groups were again tested. Their results were statistically compared. I also looked at related findings of other researchers. Finally, aspects for possible future research will also be considered. / English Studies / MA - (Specialisation in TESOL)