Impact of the Size of Modules on Target Acquisition and Pursuit for Future Modular Shape-changing Physical User Interfaces

International audience; Shape-changing User Interfaces (UIs) explore the ability of a UI to change its physical shape to support multiple interaction modalities for users’ input and/or system’s output. An approach currently studied to implement such interfaces at a high resolution is based on mm-sized, round, and self-actuated modules. The problem we tackle in this paper is to find the range of usable sizes of such modules, to better inform the trade-off between usability and technological feasibility. We assessed four sliders in a controlled user study: a standard slider and three sliders made of mock-up rounded modules of ø1 mm, ø2.5 mm, and ø5 mm. Experimental results show that (1) ø5 mm modules significantly impair performance for the pursuit task and subjective perception for both tasks, (2) performance increases when the size of modules decreases, but (3) users reportedly enjoyed the haptic feedback provided by ø1 mm to ø2.5 mm modules. These results provide deeper understanding on the impact of the size of modules on performance and subjective perception to inform current technological development of physical user interfaces made of small robotic modules.