Typing performance evaluation with multimodal soft keyboard completely integrated in commercial mobile devices

Recently touch screens are widely used for mobile devices to provide intuitive and natural interactions with hands and fingers. However, the lack of tactile responses makes it difficult for users to get key-click confirmations during text entry with soft keyboards. This paper examines the effect of tactile feedback on typing performance with the soft QWERTY keyboard, the most commonly-used, multi-finger text entry and thumb typing methods in mobile devices. In order to investigate the typing performance, we implemented tactile feedback functions by embedding multiple piezoelectric actuators that was attached under the touchscreen to simulate the key-click effect in commercial mobile platforms, MS Surface Pro (tablet) and Nokia Lumia520 (phone). We conducted an experiment of transcription tasks to measure typing performance and user preference. The experiments involved transcribing given phrases with three feedback conditions: visual only, visual with audio, and visual with tactile. The results showed that the typing performance (KSPC, WPM, UER, CER) has been significantly improved by adding tactile feedback to the existing visual display on a commercial tablet and phone. A further quantitative analysis by questionnaire also showed that all of the participants preferred tactile or aural feedback to visual feedback only. This study thus provides researchers and designers with practical guidelines regarding tactile feedback on commercial mobile devices.