SituFont: A Just-in-Time Adaptive Intervention System for Enhancing Mobile Readability in Situational Visual Impairments

Situational visual impairments (SVIs) significantly impact mobile readability, causing user discomfort and hindering information access. This paper introduces SituFont, a novel just-in-time adaptive intervention (JITAI) system designed to enhance mobile text readability by semi-automatically adjusting font parameters in response to real-time contextual changes. Leveraging smartphone sensors and a human-in-the-loop approach, SituFont personalizes the reading experience by adapting to individual user preferences, including personal factors such as fatigue and distraction level, and environmental factors like lighting, motion, and location. To inform the design of SituFont, we conducted formative interviews (N=15) to identify key SVI factors affecting readability and controlled experiments (N=18) to quantify the relationship between these factors and optimal text parameters. We then evaluated SituFont's effectiveness through a comparative user study under eight simulated SVI scenarios (N=12), demonstrating its ability to overcome SVIs. Our findings highlight the potential of JITAI systems like SituFont to mitigate the impact of SVIs and enhance mobile accessibility.