Abstract-Inspection methods and cheap self-reporting procedures have been significantly employed in the field of HumanComputer Interaction for assessing the usability of interfaces, systems and technologies. However, there is a tendency to overlook aspects related to the context and features of the users during the usability assessment process. This research introduces the concept of mental workload as an aid to enhance usability measurement. A user-study has been designed and executed in the context of human-web interaction. The aim was to investigate the relationship between the perception of usability of three popular web-sites, and the mental workload imposed by a set of typical tasks executed over them. Scores obtained with the System Usability Scale were compared to the mental workload scores obtained from the NASA Task Load Index and the Workload Profile assessment procedures. Findings suggest that perception of usability and mental workload are likely to be two nonoverlapping constructs, and there is no clear evidence of their interaction. They measure two different aspects of human-system interaction and therefore they could be jointly employed to better describe user experience.
Abstract-Digital systems have been rapidly evolving within highly dynamic and unstructured environments, where the lack of a central authority forces entities to interact with each other through collaboration and negotiation. Digital agents often use Trust models in order to compute the level of trustworthiness of the partner they want to collaborate with. Unfortunately, due to the evolution speed of open and collaborative environments, the trustworthiness of an agent varies over time, and as a result, Trust models must be continuously adapted to the changing context. In this work we address the problem by presenting a self-adaptive model for Trust computations. In particular, the proposed methodology seeks to continuously align the trust model in force with the changing context in Web 2.0 dynamic applications such as forums, blogs, p2p systems. The self-adaptation is reflected in the auto-organisation of the Trust function to obtain an accurate degree of agents' trustworthiness.
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