Investigating 3D Selection Performance While Running in Extended Reality: an In-depth Study of the Effect of Speed.

We explore how running speed affects target selection in immersive environments. Through a Fitts' tapping task, we investigate direct touch selections while participants are standing or running (at speeds up to 9 km/h). We conduct a multifaceted controlled study (n=22) to understand the effect of speed, pointing phase, and foot-strike on selection performance. We find that speed dramatically increases movement time, error rate, perceived exertion, and task load. The increased movement time is driven by the correction phase, which doubles in duration at 9 km/h, while the ballistic phase remains stable. Our exploratory analysis further reveals that a higher cadence reduces the error rate at lower speeds (4.5 km/h), while this effect disappears at higher speeds (9 km/h), as participants' motor control in target selection is significantly disrupted by the movement oscillations. As the selection error rate quickly exceeds 30% when speed increases, even with accurate, fast external tracking, we argue that direct touch interaction is likely inappropriate for running. Further efforts are needed to facilitate selection interaction at higher running speeds.