Both Sides Now: Both Height and Width of the Target Matter for Applying Fitts’ Law to Pointing Using a Mouse

Research on target acquisition has focused on two features of the task environment – the distance moved and the size of the target in the direction of movement. The present research examined the effect of the size of the target in the direction orthogonal to the direction of movement (typically called the target height) on the time to move to a target. The experiment varied the Index of Difficulty (ID) (by varying the distance moved and the target width) and the target height in a task in which participants moved a cursor from a starting point to the target. The results found that (1) movement time was linearly related to ID at each of three levels of target height, (2) movement time increased as target height decreased, and (3) the slope of the function relating movement time to ID decreased as target height decreased. The discussion addresses two possible explanations for the results, how Fitts’ Law might be modified to take target height into account, and how the results could be applied to user interface design.

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Fitting Motivation to Fitts’ Law : Effect of a Penalty Contingency on Controlled Movement

Proceedings of the Human Factors and Ergonomics Society Annual Meeting ◽

10.1177/1541931218621061 ◽

2018 ◽

Vol 62 (1) ◽

pp. 265-269 ◽

Cited By ~ 1

Author(s):

Douglas J. Gillan ◽

Randolph G. Bias

Keyword(s):

Movement Time ◽

Movement Control ◽

Target Size ◽

Movement Behavior ◽

Target Acquisition ◽

Computer Screen ◽

Fitts Law ◽

Starting Point ◽

Movement Distance ◽

Index Of Difficulty

An experiment examined the effect of a penalty on performance of target acquisition movements, focusing on overall movement time, the fit of the data to Fitts’ Law, and ballistic and homing submovements. Fitts’ Law, MT = a + b[Index of Difficulty], where Index of Difficulty (ID) = log2[Movement distance/target size], focuses on the control of the movement by external stimuli, rather than the consequences of a movement. In this study, participants moved a cursor on a computer screen from a starting point to a target with movement distance and target size varying systematically. In the Penalty condition, when the movement missed the target, the computer screen went blank and the next trial was delayed for 30 seconds. In the Nonpenalty condition, participants did not receive a penalty for missing the target. The results showed that receiving a penalty led to higher movement times, a higher Fitts’ Law slope parameter, fewer errors, and fewer nonerror overshoots of the target. Also, receiving penalties resulted in target acquisition movements with less time spent in the ballistic submovement. The results show that consequences of a movement control movement behavior.

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