Control of a trackball by the chin for communication applications, with and without neck movements

The overall aim was to evaluate whether a trackball could be used for communication by people who cannot speak due to severe motor impairment. The precision of trackball control by isolated jaw movements or a combination of jaw and head movements was evaluated in 18 healthy physical-education students, free of overt symptoms of craniomandibular dysfunction. The participants were asked to operate a trackball using the chin to type a standard text of four short sentences. There were two experimental situations: nine participants performed the typewriting task with their heads fixed; the other nine performed this task with free head movements. Trackball operation moved to the cursor over an alphabetical keyboard displayed on a computer screen and character selection was made by depression of the left-hand click button using the chin. Participants were asked to perform the task as quickly and accurately as possible. Result showed that those with free head movement typed the test significantly faster than those restricted to using only their jaw muscles. The mean time per character selection was 2.4 s (SD 0.3) for the group with free head movement and 2.7 s (SD 0.3) for the group using only jaw muscles. Group scores were not significantly different with regard to accuracy. It is suggested that a chin-operated trackball could be used for communication applications both with and without neck movements.