On the Relationship between Perception of Usability and Subjective Mental Workload of Web Interfaces

Inspection methods and cheap self-reporting procedures have been significantly employed in the field of Human-Computer 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 non-overlapping 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.