Designing Smartphone-Based Virtually Extended Displays Based on the Field of View of Head-Mounted Displays

Smartphones are designed for portability, allowing users to access various content anytime and anywhere. However, their display size is inherently limited. When using a head-mounted display (HMD) together with a smartphone, it becomes possible to add content around the smartphone using the HMD’s spatial display, effectively extending the screen beyond the smartphone’s physical display via a virtual surface. While prior studies have investigated how the size of such a virtually extended display (VED) affects spatial memory, they have not sufficiently considered that the visual characteristics of the VED, as perceived by users, vary depending on the HMD’s field of view (FOV). In this study, we investigated how the HMD’s FOV and the size of the VED in an AR environment affect spatial memory, workload, and user experience. Our results show that the presence of the VED and larger displays generally improve navigation performance and user experience, although these benefits become limited under narrow FOV conditions. Notably, the display that is as large as possible while remaining fully within the FOV provides the most balanced performance across spatial memory, workload, and user experience, indicating a sweet spot. This sweet spot varies slightly depending on how users perceive changes in display size and shape, as well as their familiarity with the screen sizes of devices they use in daily life.