Investigating the Effect of Encumbrance on Gaze- and Touch-based Target Acquisition on Handheld Mobile Devices

The potential of using gaze as an input modality in the mobile context is growing. While users often encumber themselves by carrying objects and using mobile devices while walking, the impact of encumbrance on gaze input performance remains unexplored. To investigate this, we conducted a user study (N=24) to evaluate the effect of encumbrance on the performance of 1) Gaze using Dwell time (with/without visual feedback), 2) GazeTouch (with/without visual feedback), and 3) One- or two-hand touch input. While Touch generally performed better, Gaze, especially with feedback, showed a consistent performance regardless of whether participants were encumbered or unencumbered. Participants' preferences for input modalities varied with encumbrance: they preferred Gaze when encumbered, and touch when unencumbered. Our findings enhance understanding of the effect of encumbrance on gaze input and contribute towards selecting appropriate input modalities in future mobile user interfaces to account for situational impairments.