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Modern technologies are increasingly enabling interactions between people who have never met face-to-face. In some cases, such as e-commerce, user-system interactions even replace human interactions. With the introduction of such systems came a widely publicised lack of trust online. In response, many researchers have focused on how to increase users' trust perceptions. Taking a systemic perspective, this thesis posits that long-term acceptance may largely depend on users' ability to make correct trust decisions rather than on high trust in the short term. Further shortcomings of HCI trust research were identified in a critical literature review: current trust research (1) is mostly based on users' self-reports, (2) lacks a coherent conceptual basis, and (3) focuses on cognitive trust, even though it is well established that trust is also based on affective reactions to interpersonal cues. To overcome these limitations, this thesis makes theoretical, methodological and empirical contributions. It (i) introduces an integrated framework for trust in mediated interactions that unifies existing HCI trust research, (ii) explores novel behavioural trust measures, and (iii) reports a series of experiments on users' ability to make correct trust decisions and on the effect of mediated interpersonal cues on trust and usability. The experiments on trust in e-commerce found that users could differentiate trustworthy from less trustworthy vendors, but only after a detailed exploration of a site. Judgements based on an inspection of the home page alone were not better than chance. Facial photos of assistants (which are commonly used by online vendors, but rarely researched) were found to affect users' self-reported trust in a vendor only when just the home page was inspected. No lasting negative effect of photos was found on task performance. For user trust in a human advisor interpersonal cues were researched in the form of video, avatar, audio, and photo representations. It was found that video could interfere with users' preference for trustworthy advice. An increase in risk led to an increase in interference. The avatar did not result in an increase in trust relative to other representations; rather there was some evidence for a marginally negative effect of this representation on trust. All representations that contained visual or para-verbal interpersonal cues (including the avatar) were rated as being more friendly and enjoyable than text-only representations.

Ziel der Arbeit war die Entwicklung eines Emotions- und Arbeitsbeanspruchungsmodells, welches die Emotionen von Menschen innerhalb des Fluglotsenkontextes, berechnen und vorhersagen kann. Das Modell beruht auf folgenden Erkenntnissen: emotionale Episoden und kognitive Prozesse beeinflussen sich gegenseitig, emotionale Episoden passen sich variabel an die Situation und die Lebensumstände an und emotionale Episoden sind stark abhängig von Persönlichkeitsfaktoren. Das Modell wurde sowohl theoretisch erläutert als auch experimentell mit Hilfe von verschiedenen Experimenten validiert. Dabei wurden subjektive (Fragebogen) und objektive (Pupillometrie) Messmethoden verwendet. Basis der Experimente bildete eine selbst implementierte Simulation, welche eine vereinfachte Fluglotsenaufgabe nachbildet. Es wurden drei verschiedene Experimente durchgeführt, welche zum einen den Einfluss der Aufgabenschwierigkeit auf die Emotion, den Einfluss der Emotion auf die Leistung und die Vergleichbarkeit von Simulation und realer Fluglotsentätigkeit untersuchten. Die Vergleichbarkeit und letztendliche Validierung des Modells erfolgte mit Hilfe von aktiven Fluglotsen, welche die Simulation in zwei unterschiedlichen Sessions ausführten und ihre Experteneinschätzung zum gegebenen Experiment gaben. Die Sessions bestanden zum einen aus einer neutralen und einer emotional beeinflussten Session. Das Experiment ergab gute Varianzaufklärungen in der Müdigkeit und in der negativen Stimmung der untersuchten Probanden. Das Arbeitsbeanspruchungsmodell zeigte, dass es kognitive Einflüsse vorhersagen kann, wobei vor allem die unterschiedlichen Lichtverhältnisse einen einschränkender Faktor in der Vorhersage darstellten. Die Auswertung der Validierung zeigt, dass Fluglotsen weniger erschöpft und kognitiv beansprucht von der Simulationsaufgabe waren als studentische Probanden. Generell kann allerdings gesagt werden, dass das Modell und dessen gefundene Einflüsse in vielen erhobenen Faktoren bestätigt wurde. Damit bietet das in der Arbeit beschriebene Modell eine gute Grundlage für die Vorhersage von emotionalen Einflüssen innerhalb kognitiv belastender Aufgaben, wie zum Beispiel Aufgaben von Fluglotsen.

An experiment was conducted to determine the effects of subjective culture on the usability of computerized systems. The results of the experiment did not provide sufficient evidence to conclude that any of the tested cultural dimensions affected the usability of the product. Analysis of the results indicated that the differences in scores could have been attributable to variables other than those tested and controlled for. This indicated a need to build a more detailed conceptual model of usability before empirical research of this nature can be effectively conducted. Consequently, further work needed to be done to identify the variables that influence usability, and the strategies for controlling for these variables under experimental conditions. Through a literature investigation, the validity of some of the proposed variables was established, and some additional variables were identified. The valid variables were then incorporated into a conceptual model of usability for use in future research endeavors. / Information systems / M. Sc.

An experiment was conducted to determine the effects of subjective culture on the usability of computerized systems. The results of the experiment did not provide sufficient evidence to conclude that any of the tested cultural dimensions affected the usability of the product. Analysis of the results indicated that the differences in scores could have been attributable to variables other than those tested and controlled for. This indicated a need to build a more detailed conceptual model of usability before empirical research of this nature can be effectively conducted. Consequently, further work needed to be done to identify the variables that influence usability, and the strategies for controlling for these variables under experimental conditions. Through a literature investigation, the validity of some of the proposed variables was established, and some additional variables were identified. The valid variables were then incorporated into a conceptual model of usability for use in future research endeavors. / Information systems / M. Sc.