Thinking aloud is widely used for usability evaluation and its reactivity is therefore important to the quality of evaluation results. This study investigates whether thinking aloud (i.e., verbalization at levels 1 and 2) affects the behaviour of users who perform tasks that involve interruptions and time constraints, two frequent elements of real-world activities. We find that the presence of auditory, visual, audiovisual, or no interruptions interacts with thinking aloud for task solution rate, task completion time, and participants’ fixation rate. Thinking-aloud participants also spend longer responding to interruptions than control participants. Conversely, the absence or presence of time constraints does not interact with thinking aloud, suggesting that time pressure is less likely to make thinking aloud reactive than previously assumed. Our results inform practitioners faced with the decision to either restrict verbalizations in usability evaluation to thinking aloud to avoid reactivity or relax the constraints on verbalization to obtain additional information.
International Journal of Human-computer Interaction, 2013, Vol 29, Issue 5, p. 351-364
thinking aloud; verbalization; usability evaluation; user testing; interruption; time constraints; reactivity