A Study of the Application of Fitts' Law to Selected Cerebral Palsied Adults

Abstract

Fitts' Law was applied to the evaluation of discrete aimed arm movements in one dimension performed by 6 adults with cerebral palsy and 6 adults with normal movement. Targets (1.27, 3.81, 6.35, 8.89 cm in width) placed at distances of 20.32, 30.48, 40.64, and 50.80 cm provided Indices of Difficulty of 2.19 to 6.32 bits. A video game was used for the signal to move. The t tests for corrected means showed that the cerebral palsied group had greater reaction and movement times than than the normal group. Linear regression analyses for pooled data and for the individual cerebral palsied subjects showed (a) no relationship between reaction time and Index of Difficulty for either group and (b) a negative, linear relationship between reaction time and Index of Difficulty for 1 cerebral palsied subject. Movement time was linearly and positively related to the Index of Difficulty for the normal group but not for the cerebral palsied group. Two cerebral palsied subjects had movement times which conformed to Fitts' Law. While the exceptions to Fitts' Law may be due to the limited range of movement and spasticity caused by severe cerebral palsy, there are indications that two of the cerebral palsied subjects were performing ballistic rather than visually guided aimed movements. Fitts' Law may still apply when the distances and target positions are individualized to conform to subjects' specific limitations and when the signal to move is auditory rather than visual.

A cross‐sectional study examining computer task completion by adolescents with cerebral palsy across the Manual Ability Classification System levels

“…This observation is consistent with the results observed by Gump et al . and Bravo et al . and suggests that when conducting computer tasks, adolescents with bilateral CP do not appear to adhere to Fitts' law.…”

Pointing with the ankle: the speed-accuracy trade-off

“…A few studies have given us ambiguous results in cerebral palsy (CP). Despite obvious limitations in fine motor control, children with congenital spastic hemiplegia—which is a common symptom in CP—are found to obey Fitts’ law (Smits-Engelsman et al 2007), whereas data analyses from two other studies in adults with CP yielded no significant adherence to the speed-accuracy trade-off (Bravo et al 1993; Gump et al 2002). …”

The Perils of Confounding Factors

“…What matters then, as we will show, is not that the confound be totally removed, but rather that its "strength" be reduced. We define X and Y as strongly confounded factors if r 2 (X, Y) > 0.9, otherwise they are weakly confounded 3 . In contrast to Guiard [14], the focus of this paper is to find designs that prevent strong confounds.…”

“…Studies include reciprocal tapping between two targets using different limbs and body parts, such as tapping pedals [9] and manipulating a cursor [15] with the feet, controlling a stylus attached to the chin with head movements [2], and moving a cursor by rolling the head [16]. More unexpected applications include pointing and dragging sequences [12], rapid elbow flexion [6], eye-gaze movements [25,21], and a study of patients with cerebral palsy [3], Fitts' pointing paradigm for the reciprocal tapping experiment [10, Experiment I] has proven to be very influential. Fitts' apparatus was comprised of two plates of width W, separated by distance D. Distance and width were systematically varied: The four different conditions of D (2,4,8,16 (in.…”

“…As noted in[14], a full form×scale design on Fitts' design for Experiment I[10] requires, e.g., W = 0.02 cm 3. The operational value of r 2 above which a confound is deemed strong or not depends of course on what is expected by the experimenter.…”