Movement time for motion-impaired users assisted by force-feedback: Effects of movement amplitude, target width, and gravity well width

This paper presents a study investigating how the performance of motion-impaired computer users in "point and click" tasks varies with target distance (A), target width (W), and force-feedback gravity well width (GWW). Six motion-impaired users performed "point and click" tasks across a range of values for A, W, and GWW. Times were observed to increase with A, and to decrease with W. Times also improved with GWW, and, with the addition of a gravity well, a greater improvement was observed for smaller targets than for bigger ones. It was found that Fitts' Law gave a good description of behaviour for each value of GWW, and that gravity wells reduced the effect of task difficulty on performance. A model based on Fitts' Law is proposed, which incorporates the effect of GWW on movement time. The model accounts for 88.8% of the variance in the observed data.