NAFIPS 2005 - 2005 Annual Meeting of the North American Fuzzy Information Processing Society Non-Intrusive Error-Correction of Text Input Chords: A Language Model Approach Frode Eika Sandnes Faculty ofEngineering Oslo University College Oslo, Norway frodes@iu.hio.no Abstract - An error-correction strategy that can be applied to existing chord-based text-entry systems is proposed. The strategy is capable of correcting 99.1% of all single bit-errors (insertions and deletions) and 98.1% of certain double bit errors (substitutions) occurring in words. The strategy compares the entered words against entries in a reference wordlist. A genetic algorithm is used to search for the close-to-optimal chord-to- character mapping in terms of single-bit errors, certain double bit-errors and mean fingers per chord (effort). The paper also explores the magnitude of the error-correcting degradation that occurs with multiple bit-errors per word. The chord-to-character mappings proposed is capable of correcting 0.6% more single-bit errors than the classic microwriter design, and one design is presented that result in about 17% fewer finger movements. I. INTRODUCTION Text entry is an important aspect of human computer interaction. Since the invention of the typewriter researchers have attempted to improve the way in which text is entered on machines. One strategy which is as old as the typewriter is the idea of chording and the chord keyboard, which was used by the US postal system more than 100 years ago [1]. Unfortunately, the popularity and the widespread use of the QWERTY keyboard suffocated most other ideas including the chording techniques [2]. However, chording did not completely vanish. Chording is currently used by stenographs that for instance take notes in courtrooms [3], where there are demands for extreme text entry rates. Further, chord keyboards have found a use among physically disabled users who find it difficult if not impossible to use a conventional two handed QWERTY keyboard [4]. For instance, users might not have the ability to move the fingers across a keyboard, or may not have both hands available. In recent years there has been a renewed interest in text entry strategies including the chord keyboard [5, 6]. Mobile users - that is, users that are on the move share many characteristics with the physically disabled users. They are operating portable miniature devices, which are operated under difficult circumstances. Numerous creative strategies have been proposed such as various multi-tap techniques [7- 11], tilt [12], virtual touch screen keyboards [13], gestures [14, 15] and icons [16], Although the chord keyboard has been around for a very long time, and it has found its specific target domain, there has not been much work published addressing the errors associated with chording and chord keyboards, besides the classic performance measurements reported by Seibel [171. Yo-Ping. Huang Dept. of Computer Science and Engineering Tatung University Taipei, Taiwan yphuang(ttu.edu.tw Errors and the correction of errors on chord keyboards are therefore the topics of this study. II. BACKGROUND A. Chord keyboards A basic one-handed chording keyboard has the following characteristics. There are five keys, where each finger on the hand is assigned a unique key. Text is entered by pressing key combinations without moving fingers between different keys on the keyboard. In contrast, such finger movements are necessary on conventional QWERTY keyboards. With five keys it is possible to enter 31 (25- 1) unique chord combinations. In other words, one can enter 31 unique symbols, which is sufficient for most English text, including the 26 letters of the alphabet, punctuation symbols, space and backspace. Strengths of chord keyboards include fast typing, as fingers remain in the same position, and eyes free operation, as the users do not need visually scan the keyboard for the desired key. Five keys can easily be accommodated on miniature devices. Fitt's law [18] can be used to demonstrate that the typing error rate is higher on devices with smaller keys than larger keys. Portable devices with full QWERTY keyboards are difficult to use and results in high error rates. Chording keys are two-state components, with the states up or down and they are naturally represented using bits with binary values. The term bits and finger-key presses will be used interchangeably in this paper. The term word will exclusively be used to refer to a literary word and not a data- word (two bytes). B. Typing Errors Research into automatic spelling error detection and correction classifies typing mistakes into three categories - deletions, insertions and substitutions [19]. Deletions occur when the author by accident, or by ignorance, omits a letter in a word. Insertions refer to the situations where the user accidentally, or out of ignorance, inserts an additional character in a word, and substitutions are situations where a user by accident, or out of ignorance, replaces a character in a word with an incorrect character. On conventional keyboards the two main sources of typing errors are inaccurate spelling and incorrect finger manoeuvres. Therefore, traditional spelling error detection and correction research focus on character level errors. Character level errors detection and correction is however not the topic of this paper. For a detailed 0-7803-9187-X/05/$20.00 ©2005 IEEE. 373