Die Dissertation thematisiert die kontextbezogene Präferenzbildung von Konsumenten. Aufsatz 1 untersucht das Substitutionsverhalten von Konsumenten in Out-of-Stock Situationen unter Berücksichtigung des Einflusses von Promotions. Die Ergebnisse zweier Online-Studien zeigen, dass sowohl Phantome als auch Promotions die Dominanzstruktur eines Choicesets verändern und somit zu systematischen Verschiebungen der relativen Präferenzen führen. Aufsatz 2 diskutiert, ob Kontexteffekte in einem hypothetischen Entscheidungsumfeld mit rein imaginären Kaufentscheidungen im Vergleich zu verbindlichen Entscheidungen mit realen Zahlungen systematisch überschätzt werden. Die empirischen Resultate belegen, dass der Ähnlichkeitseffekt in hypothetischen Studien signifikant höher ist als in Erhebungen unter Verwendung von realen Marken und verbindlichen Kaufentscheidungen inklusive tatsächlicher Zahlungsverpflichtungen für die gewählten Produkte. Aufsatz 3 untersucht, ob der „reversed similarity effect“, als die Tendenz von Konsumenten bei der Nichtverfügbarkeit von bevorzugten Produkten solche Substitute zu wählen, die der nichtverfügbaren Wahloption ähnlich sind, auch in realen Entscheidungsgegebenheiten Gültigkeit besitzt und bestätigt dies anhand von zwei empirischen Studien. Aufsatz 4 analysiert den interaktiven Effekt von Phantomen und Händlerempfehlungen auf die Präferenzbildung bei Onlinekäufen. Es zeigt sich, dass der separate Einfluss beider Faktoren nicht zwangsläufig positiv interagiert. Vielmehr bedingen sich Richtung und Stärke der gemeinsamen Wirkung durch die jeweilige Produktkategorie sowie die empfundene Wichtigkeit der enthaltenen Produktattribute. Aufsatz 5 beschäftigt sich mit Präferenzdeterminanten für biologische Produkte. Mithilfe eines Strukturgleichungsmodells kann belegt werden, dass Gesundheits- sowie Umweltmotive keinen direkten Einfluss auf die Bio-Präferenzen eines Haushalts haben, sondern durch die jeweilige Einstellung zu Bioartikeln moderiert werden. / The doctoral dissertation analyzes context-dependent preference formation of customers with regard to the influence of product- and situation-specific as well as experimental factors. Essay 1 studies preference formation of customers in out-of-stock situations by coevally considering the specific influence of promotions. The results of two online studies reveal that both phantoms and promotions induce changes in the dominance structure of a choice set, thereby systematically affecting customers’ substitution decisions. Essay 2 discusses if context effects are significantly overestimated in binding choice settings that include real payments for test products. The attained results confirm that the similarity effect is significantly higher in purely hypothetical decision environments in contrast to realistic choice setting inclusive of payment obligations for the selected products. Essay 3 attends to the question if the reversed similarity effect – as a customers’ tendency to preferably select very similar substitutes when a desired item is temporarily unavailable – also holds true in market-like choice scenarios. The results of a comprehensive online study confirm the existence of the effect in all tested product categories. Essay 4 studies the interactive effect of phantoms, i.e. unavailable choice options, and recommendations on directing customers’ choice in online purchase decisions. It can be demonstrated that the factors’ separate influence does not necessarily add up when appearing within the same choice scenario. Instead boundary conditions of the factors’ interaction are identified. Essay 5 seeks to identify determinants of customers’ preference for organic products. The results of PLS structural equation modelling show that health- as well as environmental motives do not have a direct effect on relative preferences for organic items but that their influence is fully mediated by one’s attitude towards organically produced articles.

The present thesis explores how answering questions on values in surveys could be influenced. Findings about cognitive processes occurring in general during answering questions, as well as factors that may influence the given answers are presented in the first part of the theoretical section. Afterwards, Schwartz's circular model of values is presented together with the instruments he developed to measure their importance. At the end of the theoretical section, the results of existing studies on the possibilities of influencing values are described. A series of three experimental online studies, involving nearly 600 respondents, builds on the findings presented in the theoretical section. The experiments examine the malleability of individualistic and collectivistic values based on induced changes in regulatory focus and self-construal of participants. In the first of the studies, the given values were affected by the content of previous questions, but this effect was in the opposite direction than originally anticipated. In the next two studies, the experimental manipulation did not lead to significant differences between groups. Causes of the results, limits of the conducted studies and prospects for future research are discussed in the last sections of the thesis.

This study examines the home as a context of viewing for the television programme Intersexions in the township of Ginsberg in the Eastern Cape. The central question asked is whether the household influences the interpretation of the programme. The research was mainly conducted through ethnographical methods of participant observation and focus group interviews. Six families were observed and six gender-based focus groups convened. Drawing from the work of Morley (1986) and Lull (1990) that argues that the home be taken more seriously as a context of viewing; this study posits that the home is a rule-bound micro-society that influences the interpretation of media messages. As a starting point, this study contends with the arguments that the South African government has been slow to acknowledge the extent of the problem presented by the HIV/AIDS pandemic. Much has been written about the inefficiency of state efforts to educate the public, with some pundits suggesting that government communications strategies have largely been outdated and thus resisted by audiences (Treffry-Goatley, Mahlinza & Imrie, 2013). To counter the pandemic, a large number of independent educational television serials have been launched in South Africa, and met with popular appeal since 1994. Furthermore, this development is in line with global trends of high audience ratings for Entertainment- Education (EE) programmes (Singhal et al., 1993). To investigate complex issue of EE reception by audiences in this burgeoning area of study, the programme at the centre of this study, Intersexions, is a good example. The serial, which concluded its second season in August 2013, is second to only the established soap opera, Generations, in television ratings in South Africa. Therefore, the impressive ratings garnered by educational serials in South Africa are a chance for audience studies to study audiences in context. This research investigates Intersexions using the understanding that television audiences must be analysed in "cultural and historic specific" sites because the struggle to make meanings of texts takes place at the moment when the text and subject meet (Fiske, 1987). This research investigates the assumption that the meanings made by audiences depend not just on the text, but also on environment. This means that the research delves into the situational context in which media are used and interpreted. Therefore, the central aim of this study is to analyse television viewing of the entertainment education programme, Intersexions, in the natural setting of the home, which is in line with analysing television viewers in cultural and historically specific sites.

There is a difference between the raw sensory input to the brain and our stable perception of entities in the environment. A first approach to investigate perception is to study relationships between properties of currently presented stimuli and biological correlates of perceptual processes. However, it is known that such processes are not only dependent on the current stimulus. Sampling of information and the concurrent neuronal processing of stimulus content rely on contextual relationships in the environment, and between the environment and the body. Perceptual processes dynamically adjust to relevant context, such as the current task of the organism and its immediate history. To understand perception, we have to study how processing of current stimulus content is influenced by such contextual factors. This thesis investigates the influence of such factors on visual processing. In particular, it investigates effects of temporal context in early visual processing and the effect of task context in eye movement control. To investigate effects of contextual factors on early visual processing of current stimulus content, we study neuronal processing of visual information in the primary visual cortex. We use real-time optical imaging with voltage sensitive dyes to capture neuronal population activity in the millisecond range across several millimeters of cortical area. To characterize the cortical layout concerning the mapping of orientation, previous to further investigations, we use smoothly moving grating stimuli. Investigating responses to this stimulus type systematically, we find independent encoding of local contrast and orientation, and a direct mapping of current stimulus content onto cortical activity (Study 1). To investigate the influence of the previous stimulus as context on processing of current stimulus content, we use abrupt visual changes in sequences of modified natural images. In earlier studies, investigating relatively fast timescales, it was found that the primary visual cortex continuously represents current input (ongoing encoding), with little interference from past stimuli. We investigate whether this coding scheme generalizes to cases in which stimuli change more slowly, as frequently encountered in natural visual input. We use sequences of natural scene contours, comprised of vertically and horizontally filtered natural images, their superpositions, and a blank stimulus, presented with 10 or 33 Hz. We show that at the low temporal frequency, cortical activity patterns do not encode the present orientations but instead reflect their relative changes in time. For example, when a stimulus with horizontal orientation is followed by the superposition of both orientations, the pattern of cortical activity represents the newly added vertical orientations instead of the full sum of orientations. Correspondingly, contour removal from the superposition leads to the representation of orientations that have disappeared rather than those that remain. This is in sharp contrast to more rapid sequences for which we find an ongoing representation of present input, consistent with earlier studies. In summary, we find that for slow stimulus sequences, populations of neurons in the primary visual cortex are no longer tuned to orientations within individual stimuli but instead represent the difference between consecutive stimuli. Our results emphasize the influence of the temporal context on early visual processing and consequentially on information transmission to higher cortical areas (Study 2). To study effects of contextual factors on the sampling of visual information, we focus on human eye movement control. The eyes are actively moved to sample visual information from the environment. Some traditional approaches predict eye movements solely on simple stimulus properties, such as local contrasts (stimulus-driven factors). Recent arguments, however, emphasize the influence of tasks (task context) and bodily factors (spatial bias). To investigate how contextual factors affect eye movement control, we quantify the relative influences of the task context, spatial biases and stimulus-driven factors. Participants view and classify natural scenery and faces while their eye movements are recorded. The stimuli are composed of small image patches. For each of these patches we derive a measure that quantifies stimulus-driven factors, based on the image content of a patch, and spatial viewing biases, based on the location of the patch. Utilizing the participants’ classification responses, we additionally derive a measure, which reflects the information content of a patch in the context of a given task. We show that the effect of spatial biases is highest, that task context is a close runner-up, and that stimulus-driven factors have, on average, a smaller influence. Remarkably, all three factors make independent and significant contributions to the selection of viewed locations. Hence, in addition to stimulus-driven factors and spatial biases, the task context contributes to visual sampling behavior and has to be considered in a model of human eye movements. Visual processing of current stimulus content, in particular visual sampling behavior and early processing, is inherently dependent on context. We show that already in the first cortical stage, temporal context strongly affects the processing of new visual information and that visual sampling by eye movements is significantly influenced by the task context, independently of spatial factors and stimulus-driven factors. The empirical results presented provide foundations for an improved theoretical understanding of the role of context in perceptual processes.

Messinstrumente stellen in der wissenschaftlichen Forschung ein wesentliches Element zur Erkenntnisgewinnung dar. Das Besondere an Messinstrumenten im Large-scale Assessment in der Bildungsforschung ist, dass diese normalerweise für jede Studie neu konstruiert werden und dass die Testteilnehmer verschiedene Versionen des Tests bekommen. Hierbei ergeben sich potentielle Gefahren für die Akkuratheit und Validität der Messung. Um solche Gefahren zu minimieren, sollten (a) die Ursachen für Verzerrungen der Messung und (b) mögliche Strategien zur Optimierung der Messinstrumente eruiert werden. Deshalb wird in der vorliegenden Dissertation spezifischen Fragestellungen im Rahmen dieser beiden Forschungsanliegen nachgegangen. / Measurement instruments are essential elements in the acquisition of knowledge in scientific research. Special features of measurement instruments in large-scale assessments of student achievement are their frequent reconstruction and the usage of different test versions. Here, threats for the accuracy and validity of the measurement may emerge. To minimize such threats, (a) sources for potential bias of measurement and (b) strategies to optimize measuring instruments should be explored. Therefore, the present dissertation investigates several specific topics within these two research areas.