Developing a Personalized Virtual Coach for Emotional Eaters 39 2 Figure 4 | Screen capture from the usability test: eye tracking gaze plot video Usability evaluation with eye-gaze tracking Next, a usability evaluation of the second improved version of the clickable prototype was conducted among the target group (N=10). Participants, procedure & materials: Task scenarios were created. Tasks were presented as short stories to give more context. In total, ten participants [50] volunteered to perform a test with eight tasks. Among the ten participants, five were university students studying behavioural sciences, three were self-declared) emotional eaters and two were user interface designers. Participants were recruited via the Facebook social network used by the students. The usability test took around 30 minutes. Participants first received a prebriefing on the goals of the usability test and the nature of volunteer participation. Next, users executed the task scenarios followed by a post-test interview. During the usability tests (Fig. 4), participants were monitored by eye tracking, using a ‘Tobii Mobile Device Stand’ (MDS) [51], followed by an interview in accordance with the Retrospective Think Aloud Method [52]. A calibrated eye tracker (one that follows the eye pupils of a test user) registered what the user is looking at while performing each task using the second clickable prototype. The evaluator is able to see what parts of the interface the user is looking at, even if the test user scrolls, or zooms in while interacting with the user interface [51]. The results are plotted on so-called gaze plots and the evaluator is able to watch a slow-motion replay.
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