Psychomotor Efficiency in Users of Notebook Input Devices: Confirmation and Restrictions of Fitts' Law as an Evaluative Tool for User-Friendly Design

Abstract

On the basis of Fitts' law the present study examined the psychomotor efficiency for 20 experienced users of force- (trackpoint) and motion-input (touchpad) devices in clicking and dragging tasks. Beyond task difficulty the impact of input modality, practice, and task type was investigated. On the one hand, the results support Fitts' law since performance data of both input devices fitted satisfyingly with Fitts' predictions. Motion-input was found to be very robust towards task difficulty, especially in dragging tasks. On the other hand, the results were incompatible to Fitts' assumptions as target size and distance did not equally contribute to task difficulty but rather target size was a stronger contributor. Thus, the effective task difficulty in small targets was notably underestimated. For user-friendly interfaces, button widths of over 0.5 cm should be provided, especially when distances farther than 7.5 cm are inevitable.

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