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Chording is a technique that allows users to enter text without visual feedback. Traditional chording strategies are hampered by the substantial training effort required as users need to memorize chords. In this study an alternative chording scheme that uses spatial mnemonics to accelerate learning is proposed. Users mentally visualize the appearance of each character as a 3 x 3 pixel grid. The grid is input as a sequence of three chords. However, a problem with this approach is that the error probability accumulates across the three chords and the total error rate is therefore higher than for traditional chording. This study addresses to what degree these errors can be automatically corrected. Unlike traditional text correction approaches that operate with characters as the atomic unit, the redundancy available in the chords is used to improve the error correction. Experimental evaluations show that the strategy is capable of correcting 18.5% of all individual character construction errors. Next, the strategy is capable of correcting approximately twice as many word-level errors as MSWord, namely 69.5% of all substitution errors and 33.3% of all insertion errors. The strategy has at least two target audiences: users who need to devote their visual attention to other tasks and blind and visually impaired users who are unable to use visual intensive text entry techniques.

Keywords: mobile text entry, chording, error correction, miniature device, eyes-free operation, spatial mnemonics, visually impaired users

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Received August 16, 2005; accepted January 17, 2006.
Communicated by Jhing-Fa Wang, Pau-Choo Chung and Mark Billinghurst.