In single-switch communication, user input consists of repeated clicks, distinguished only by timing information; these clicks might be generated by pressing a button or blinking. For instance, the range of movement of individuals with severe motor impairments may be limited to a single muscle. Alternatively, a crowded or jostled mobile technology user may be able to click precisely while other actions are difficult or sloppy. A single switch may also be useful when information conveyed, such as a PIN, is sensitive and hand location on a normal keyboard might betray this content. Our method, “Nomon” (e.g. Figure 1), expands the application scope of existing methods and facilitates faster writing than the most common single-switch writing interface.

Existing single-switch communication methods include scanning [1, 2] and One-Button Dasher [3, 4]. (Morse Code, in contrast, requires either click duration information or multiple switches.) These methods require options to be arranged in a particular configuration. By contrast, traditional operating systems, web browsers, and free-form applications such as drawing place options at arbitrary points on the screen. We seek a single-switch selection method that is not limited to certain forms of option placement. We want our method to work for any number of options; to be able to effectively reorder the set of selections without imposing additional cognitive load; and to allow the user to attend only to the desired target. Our method, Nomon, accomplishes these objectives. It can further automatically adapt to individuals’ clicking abilities and incorporate prior beliefs about option selection frequency.

To test our method, we developed a writing application, the Nomon Keyboard (Figure 1), and compared its performance with a popular commercial scanning interface, The Grid 2 [5] (Figure 2). We examined study participants’ writing speeds, error rates, and number of clicks made per character as well as the subjective ratings of their experiences. We found that novice users wrote 35% faster with the Nomon interface than with the scanning interface. An experienced user (author TB, with > 10 hours practice) wrote at speeds of 9.3 words per minute with Nomon, using 1.2 clicks per character and making no errors in the final text.