Evaluation of an ambiguous-keyboard prototype scanning-system with word and character disambiguation

Ambiguous keyboards are common in small-size devices such as mobile phones, but they can be applied to other fields such as Augmentative and Alternative Communications, and specifically addressed to people with severe motor disabilities. This research proposes a novel alternative to assign letters to keys, where letters with similar graphical characteristics are grouped into the same key, leading to families of four, three and two-key simple and easy-to-learn layouts. All layouts have been analyzed for a scanning system that implements a word and a character disambiguation algorithm using only one switch as input device. With the best three-key layout, the text entry speeds predicted were 16.7 wpm using word disambiguation and 10.8 wpm for character disambiguation, with a 0.5 seconds scan period. In an experiment conducted with 6 participants and dynamic scan period, average entry speeds reached 12.2 and 6.3 wpm respectively. The top speeds reached by single participants were 16.9 and 8.3 wpm.