Don't disturb me: understanding secondary tasks on public displays

A growing number of displays provide information and applications in public spaces. Most applications today are considered to pose one task to the user, such as navigating a map. In contrast to such primary tasks, secondary tasks have yet received little attention in research, despite practical relevance. For example, a secondary task might occur by displaying special ticket offers to a tourist browsing a city map for attractions. This paper investigates secondary tasks with two key-contributions: First, we describe a design space for secondary tasks on public displays, identifying dimensions of interest to application designers. Second, we present a user study with text entry and mental arithmetic tasks to assess how secondary tasks influence performance in the primary task depending on two main dimensions -- difficulty and temporal integration. We report performance (completion times, error rates) and subjective user ratings, such as distraction and frustration. Analysis of gaze data suggests three main strategies of how users switch between primary and secondary tasks. Based on our findings, we conclude with recommendations for designing apps with secondary tasks on public displays.

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