| Sumario: | To provide people with motor limitations access to technology, rehabilitation therapists identify a particular 'control site' or location on the body that can be used to operate a device. Research in the field of human-computer interaction shows that the number of skeletal joints or degrees of freedom used to control a computer input device influences movement time. It has also been suggested that for people with central nervous system pathology, reducing the degrees of freedom to complete common tasks improves functioning. This study investigated the effect of reducing the degrees of freedom required to operate a computer input device on performance. Two adapted input devices were compared in the context of a target acquisition task and a text-typing task. The devices selected involved different control sites (head versus hand/arm) and thus required control of varying degrees of freedom. To establish performance baselines, twenty-four young adults served as subjects. Total movement time for both target acquisition and typing was significantly faster when the head device was used. Data suggest that for typical young adults, reducing the degrees of freedom required to operate an input device facilitates performance by decreasing the time required to reach asymptote performance and by moderating cognitive demands for device operation. Though the hand/arm device took considerably longer than the head device for both tasks, it resulted in significantly less movement variability when acquiring a target and significantly lower error rates for typing. Subjects reported no significant difference in comfort and ease of use for the two devices. These results suggest that greater clinical attention should be given to the relationship between control site and number of skeletal joints involved when matching an individual's physical abilities to the operational requirements of a computer interface.
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