In a computer course, provided by the Royal Dutch Visio, some partially sighted older clients had difficulty operating a PC. Clients are taught to use a keyboard, which may be difficult to use for a number of older adults. Studies comparing input devices conclude that the touch screen results in the greatest task performance for older adults. However, existing research mainly compares older adults without visual impairments. An experiment was conducted which compared task performance of two input devices (keyboard and touch screen) in two age groups (younger and partially sighted older adults). Task execution times and errors were obtained in three computer tasks. The results indicate that the touch screen outperformed the keyboard in both age groups in simple point-and-tap interfaces. But, there are activities and controls that caused difficulties, e.g. entering text and using a scroll bar. ACT-R, an influential cognitive architecture, was used to model task performance of the partially sighted older computer user to better understand the use of input devices. ACT-R parameters were updated to model the effects of age-related changes and visual impairments, which are not presently part of the architecture. Keyboard and touch screen models were developed which simulated task performance in a task from the experiment. Analyses revealed a good fit between the touch screen model and older adult data, although the keyboard model needs some more refinements.
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