Application of Fitts' Law to Individuals with Cerebral Palsy

Abstract

Cerebral palsy is a condition that results in motor abnormalities as a direct consequence of injury to the developing brain. Fitts' law, which describes a speed-accuracy tradeoff in visually guided movements, has been shown to characterize the motor behavior of normal subjects during aiming tasks. To assess whether Fitts' law can also describe the aimed movements of persons with cerebral palsy, eight cerebral palsied adults participated in an aimed movement study. 12 targets were used with Indices of Difficulty ranging from 2.19 to 6.00 bits. The impact of Gan and Hoffmann's 1988 ballistic movement factor, square root(A) , and Fitts' 1954 Index of Difficulty on subject's movement and reaction times was examined using multivariate linear models. The analysis of the full data set yielded a significant effect of square root(A) on movement times and no significant adherence to Fitts' law. However, high error rates that could be the result of oculomotor problems among the subject group were noted, and the method of handling errors had a large effect on the results. Tracking eye position during a Fitts' law task would provide information regarding the effect of oculomotor difficulties on aiming tasks in the cerebral palsied subject group.

Automatic evaluation of assistive interfaces

“…al. [2] obtained a different result. In general for real life pointing tasks, motor-impaired persons are not always governed by visual feedback.…”

“…al. [2] found significant correlation between the movement time and the root of movement amplitude (Ballistic Movement Factor [17]). Gajos, Wobbrock and Weld [18] estimated the movement time by selecting a set of features from a pool of seven functions of movement amplitude and target width, and then using the selected features in a linear regression model.…”

“…In general for real life pointing tasks, motor-impaired persons are not always governed by visual feedback. Their movements seem to be more ballistic (rapid and discrete movement without visual feedback, [2]). This may be a result of their poor coordination between perception and motor-action.…”

A comparison of area pointing and goal crossing for people with and without motor impairments

“…LoPresti et al [17] showed that Fitts' law holds for neck movements by people with motor impairments, although explicit formulations using Equation 1 were not reported. Gump et al [9] argued that Fitts' law did not hold for people with Cerebral Palsy, although they noted that their data contained problematically high error rates, possibly from oculomotor problems. More recently, SmitsEngelsman et al [25] showed that children with Cerebral Palsy do, in fact, adhere to Fitts' law.…”

Automatically generating user interfaces adapted to users' motor and vision capabilities

“…It is debatable, however, whether Fitts' law applies to individuals with motor impairments. Prior work suggests that in some cases it might [29], while in others it might not [13]. Due to these concerns, we need a new approach for modeling people's individual movement characteristics.…”