Exploring the Design Space of Glanceable Smartwatch Feedback Displays: Experimental Study.

BACKGROUND: Self-monitoring technologies are commonly used to promote health behavior change, with glanceable displays offering continuous feedback throughout the day. Yet, it is still unclear how various aspects of these glanceable representations affect their interpretability and usability. OBJECTIVE: This study aimed to investigate the effects of 3 design factors-stylization, granularity, and salience-on users' ability to understand glanceable smartwatch-based feedback on daily step goals. METHODS: We conducted an online simulation study to examine how 3 design dimensions-stylization, salience, and granularity-influence the effectiveness of glanceable feedback displays. Stylization and salience were crossed in a 2×2 factorial design, while granularity varied from 1% to 20% progress increments. A total of 202 Amazon Mechanical Turk participants were randomly assigned to 1 of 16 smartwatch display conditions. In each condition, participants viewed feedback on daily step progress and estimated the level of progress shown. We measured estimation error and questionnaire-assessed perceived usability and acceptability. The collected data were analyzed using generalized estimating equations and linear regression. RESULTS: High stylization reduced accuracy (+4.52 error points; P<.001) and negatively affected perceptions across 6 dimensions, including comprehension (P=.003), complexity (P<.001), and usability (P=.001). Granularity had a nonlinear effect: error was lowest around 5%-10%, with sharp increases at 20%. The 10% level also received the most favorable ratings, for example, comprehension (+0.656; P=.003). Salience had no effect. Previous smartwatch users were less accurate than never-users (+7.46 points) but rated displays as more useful (P=.002) and easier to focus on (P<.001). Current users gave similarly positive ratings on attention and usefulness. CONCLUSIONS: These findings could help researchers design effective glanceable smartwatch feedback displays and expand the design space for glanceable feedback.