Abstract: Previously we demonstrated that after 400 minutes of practice, ten novices averaged over 26 words per minute (wpm) for text entry on the Twiddler one-handed chording keyboard, outperforming the multi-tap mobile text entry standard. Here we present an extension of this study that examines expert chording performance. Five subjects continued the study and achieved an average rate of 47 wpm after approximately 25 hours of practice in varying conditions. One subject achieved a rate of 67 wpm, equivalent to the typing rate of the last author who has been a Twiddler user for ten years. We provide evidence that lack of visual feedback does not hinder expert typing speed and examine the potential use of multiple character chords (MCCs) to increase text entry speed. We demonstrate the effects of learning on various aspects of chording and analyze how subjects adopt a simultaneous or sequential method of pushing the individual keys during a chord.
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