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There are many situations in which the user cannot devote full visual attention towards her actions on a mobile device (Brewster et al., 2003). For example, social protocols often discourage multi-tasking during certain situations (e.g., business meeting); as a result, the user often must reply to emails in a discrete manner, if done at all. The high visual demand of some tasks or environments also might cause a situationally-induced impairment (Sears, Lin, & Jacko, 2003) which, for example, could prevent the user from quickly sending a message while walking. Thus, the ability to interact with mobile devices sight-free could allow the user to complete important tasks without needing to pull much visual attention away from the main task towards the text entry method.
We present our iterative design of Escape-Keyboard, a soft keyboard which supports sight-free text entry on mobile touch-screen devices without requiring any hardware modification to the device (Figure 1a). We designed Escape-Keyboard for one-handed use, where the user enters text using the thumb of the hand holding the device. Based on the results from two small formative studies, we determined a layout with four target regions on the screen (Figure 1b). The user can place her thumb easily in these regions without looking at the device or needing any physical guides. To type a letter, the user touches one of the four regions, and then performs a flick gesture in one of eight directions as indicated by the Escape icon (Yatani et al., 2008).
Figure 1. (a) The Escape-Keyboard. (b) Initial and (c) final layouts determined through our iterative design process.
We examined the performance of Escape-Keyboard through two experiments and a theoretical analysis. The first evaluation included 16 sessions in which participants typed in sighted and sight-free conditions; its results highlighted the importance of reducing the mental load with using Escape-Keyboard to improve user performance over time. We then implemented and evaluated features specifically designed to mitigate the issue caused by the user’s unfamiliarity with Escape-Keyboard. Finally, to examine the upper bound of the performance, we conducted a theoretical analysis of the entry speed of Escape-Keyboard. Our work demonstrates that marking gestures can be used from four specific target areas on the screen to create a sight-free text-entry method with low physical demand. Additionally, the layout can adopt a QWERTY-like design (Figure 1c) to create a familiar interface that is easy to learn, without compromising much in terms of user performance.