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

Abstract

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.