JOURNAL ON MULTIMODAL USER INTERFACES, vol.13, no.4, pp.321-334, 2019 (SCI-Expanded)
Jitter is an inevitable by-product of gaze detection. Because of this, gaze typing tends to be a slow and frustrating process. In this paper, we propose SliceType, a soft keyboard that is optimized for gaze input. Our main design objective is to use the screen area more efficiently by allocating a larger area to the target keys. We achieve this by determining the keys that will not be used for the next input, and allocating their space to the adjacent keys with a merging animation. Larger keys are faster to navigate towards, and easy to dwell on in the presence of eye tracking jitter. As a result, the user types faster and more comfortably. In addition, we employ a word completion scheme that complements gaze typing mechanics. A character and a related prediction is displayed at each key. Dwelling at a key enters the character, and double-dwelling enters the prediction. While dwelling on a key to enter a character, the user reads the related prediction effortlessly. The improvements provided by these features are quantified using the Fitts' law. The performance of the proposed keyboard is compared with two other soft keyboards designed for gaze typing, Dasher and GazeTalk. Thirty seven novice users gaze-typed a piece of text using all three keyboards. The results of the experiment show that the proposed keyboard allows faster typing, and is more preferred by the users.