A comparison of consecutive and concurrent input text entry techniques for mobile phones

The numeric keypads on mobile phones generally consist of 12 keys (0-9, *, #). Ambiguity arises when the 36-character alpha-numeric English alphabet is mapped onto this smaller number of keys. In this paper, we first present a taxonomy of the various techniques for resolving this ambiguity, dividing them into techniques that use consecutive actions to first select a character grouping and then a character from within that grouping, and those that use concurrent actions to achieve the same end. We then present the design and implementation of a chording approach to text entry that uses concurrent key presses. We conducted a controlled experiment that compared this chording technique to one-handed and two-handed versions of the commonly used MultiTap technique. The results show that the concurrent chording technique significantly outperforms both versions of the consecutive action MultiTap technique.