The Effects of Hand Strength on Pointing Performance

Pointing tasks form a significant part of human-computer interaction in graphical user interfaces. Fitts’ law (Fitts, 1954) and its variations (Mackenzie, 2003) are widely used to model pointing as a sequence of rapid aiming movements, especially for able-bodied users. Fitts’ Law predicts the movement time as a function of the width and distance to the target. This law is found to be very robust and works in many different situations (even in space and under water). However the application of Fitts’ Law for people with motor impairment is less clear. We have investigated also how the pointing performance of people with motor impairment varies from their able-bodied counterparts. In particular, we have studied how physical strength affects the pointing performance of people with and without motor impairment for different input devices. We have used this study to develop a simulator to help with the design and evaluation of assistive interfaces (Biswas and Robinson, 2008b). The simulator embodies both the internal state of a computer application and also the perceptual, cognitive and motor processes of its user. It takes a task definition and locations of different objects in an interface as input. It then predicts possible eye movements and cursor paths on the screen and uses these to predict task completion times. We hope this study will be helpful to understand and analyse the interaction patterns of people with motor impairment and design better assistive interfaces for them. It will also help in explaining motor action and developing better motor-behaviour models for motor impaired users.