SAK: Scanning ambiguous keyboard for efficient one-key text entry

The design and evaluation of a scanning ambiguous keyboard (SAK) is presented. SAK combines the most demanding requirement of a scanning keyboard—input using one key or switch—with the most appealing feature of an ambiguous keyboard—one key press per letter. The optimal design requires just 1.713 scan steps per character for English text entry. In a provisional evaluation, 12 able-bodied participants each entered 5 blocks of text with the scanning interval decreasing from 1100 ms initially to 700 ms at the end. The average text entry rate in the 5th block was 5.11 wpm with 99% accuracy. One participant performed an additional five blocks of trials and reached an average speed of 9.28 wpm on the 10th block. Afterwards, the usefulness of the approach for persons with severe physical disabilities was shown in a case study with a software implementation of the idea explicitly adapted for that target community.

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