Fitts' law is a robust model of human psychomotor behavior developed in 1954. The model is based on time and distance. It enables the prediction of human movement and human motion based on rapid, aimed movement, not drawing or writing.
It seems intuitive that movement time would be affected by the distance moved and the precision demanded by the size of the target to which one is moving. Fitts discovered that movement time was a logarithmic function of distance when target size was held constant, and that movement time was also a logarithmic function of target size when distance was held constant. Mathematically, Fitts' law is stated as follows:
MT = a + b log2(2A/W)
where
The foundations of Fitts' Law are discussed in the following lecture slides:
Fitts' Law has been used in many experimental settings. See the following lecture slides on Fitts' original experiments:
Commonly in HCI, Fitts' Law is used to evaluate input devices. For example, see the following lecture slides on the 1978 Card, English, and Burr experiments: An in-class exercise and an experiment were performed as part of this project.
Results of Fitts' original experiments:
Results of the 1978 Card, English, and Burr experiments:
One of our lecture slides talks about applications of Fitts’ Law.
Fitts' law is an effective method of modeling rapid, aimed movements, where one appendage (like a hand) starts at rest at a specific start position, and moves to rest within a target area. The law can be used to assist in the design of user interfaces. It can also be used to predict the performance of operators using a complex system, assist in allocating tasks to operators, and predict movement times for assembly line work. However, just as there are advantages, there are also disadvantages.
One such disadvantage is that Fitts' law predicts movement in only one dimension. Fitts' original experiments tested human performance in making horizontal moves toward a target. Both the amplitude of the move and the width of the terminating region were measured along the same axis. It follows that the method is inherently one-dimensional. So, when dealing with two-dimensional target acquisition tasks, new interpretations of "target width" must be considered. Another major deficiency is the absence of a consistent technique for dealing with errors. Researchers have developed a method to handle errors, but it has been largely ignored because of its complexity. Still another disadvantage is a lack of consensus in the measures found in across-study comparisons.