Simulating an extendable tangible slider for eyes-free one-handed interaction on mobile devices

Sliders are widely used on mobile devices. Envisioning mobile devices that can dynamically deform to raise tangible controls from the screen surface, tangible sliders offer the benefit of eyes-free interaction. However, reaching for distant values with one hand is problematic: users namely need to change their handgrip, which is not comfortable. To overcome this problem, this paper sets out to experimentally study an extendable tangible slider to support one-handed clutching. The tangible slider's knob extends to maintain the thumb's movement within its comfortable area. We first built a low-fidelity prototype made of a knob long enough to allow clutching. This low-fidelity prototype significantly improves performance when reaching distant targets, as compared to a standard tangible slider. We then built a higher-fidelity prototype, introducing actuation and allowing for a shorter knob. When used for clutching, the knob moves back towards the users' thumb. Experimental results show that the motion of the actuated knob does not interrupt eyes-free interaction during manipulation. In comparison, a graphical extendable slider performed 0.9s slower due to the required visual attention. However, the results suggest that the motion of the actuated knob affects performance, as the higher-fidelity prototype performed 0.6s slower than the low-fidelity prototype.