The Effects of Physical Attributes of Computer Interface Design on Novice and Experienced Performance of Users with Physical Disabilities

Abstract

It is well accepted that with even very simple tasks, a user's performance with a cursor control device improves substantially over some period of time before stabilizing. Although no systematic studies are available concerning how particular attributes of screen or device design affect the rate at which users learn to interact with a system, past studies with input devices have shown that the overall period of time required to learn to physically interact with a system is generally quite short. Hence the lack of attention paid to the “learning” phase with respect to physical interaction is probably justified. For users with mobility impairments, however, not only may the overall physical learning phase be significantly longer than for nondisabled users, but certain features of the interface design may require a longer learning period than others. Depending on how different “initial” performance is from “practiced” performance, systems meant for “walk up and use” or casual use may need to be designed differently to allow easy access for persons with mobility impairments. In addition, adaptive interfaces which change the physical design of features over time as a user becomes more proficient may facilitate access for individuals with impaired motor control. Twenty persons with impaired hand and arm function (as a result of spinal cord injury) performed a target acquisition task with five cursor control devices. The task required that the user select targets of different sizes and distances using both “point and click” and “drag” modes of interaction. Time and errors were recorded. The results indicate not only that some physical design attributes negatively effect performance, but that the magnitude of the effects differ for “initial” performance and “practiced” performance. In fact, in some cases attributes which had no effect once performance had asymptoted were shown to have a significant effect on novice performance. Also, some features required significantly longer periods of time for the users to become proficient at using than others. The implications for interface design are discussed.