Designing and Evaluating Head-based Pointing on Smartphones for People with Motor Impairments

Abstract

Head-based pointing is an alternative input method for people with motor impairments to access computing devices. This paper proposes a calibration-free head-tracking input mechanism for mobile devices that makes use of the front-facing camera that is standard on most devices. To evaluate our design, we performed two Fitts' Law studies. First, a comparison study of our method with an existing head-based pointing solution, Eva Facial Mouse, with subjects without motor impairments. Second, we conducted what we believe is the first Fitts' Law study using a mobile head tracker with subjects with motor impairments. We extend prior studies with a greater range of index of difficulties (IDs) [1.62, 5.20] bits and achieved promising throughput (average 0.61 bps with motor impairments and 0.90 bps without). We found that users' throughput was 0.95 bps on average in our most difficult task (IDs: 5.20 bits), which involved selecting a target half the size of the Android recommendation for a touch target after moving nearly the full height of the screen. This suggests the system is capable of fine precision tasks. We summarize our observations and the lessons from our user studies into a set of design guidelines for head-based pointing systems.