Fitts' Law as a Research and Design Tool in Human-Computer Interaction

Bibliographical Information:
I. Scott MacKenzie. 1992. Fitts' law as a research and design tool in human-computer interaction.Hum.-Comput. Interact. 7, 1 (March 1992), 91-139. DOI=10.1207/s15327051hci0701_3 http://dx.doi.org/10.1207/s15327051hci0701_3

URL:
http://dl.acm.org/citation.cfm?id=1461857

This paper is an outline on the principles of Fitts' Law, and how it can be applied to the domain of Human-Computer Interaction. Previously, this research and the subsequent applications had been applied only to the domains pertaining to psychology, measuring the cognitive effects of differing "targets". The main focus is in quantifying task completion time through a mathematical formula that depends on both the distance that the test subject is expected to traverse and the size of the target he or she is expected to "hit". The formula that Fitts developed is shown below:

 

Where T is the average time it will take the subject to perform the task, a and b are the parameters of the particular model, ID is what is called the "index of difficulty", which is calculated the logarithm (base 2) of twice the distance D of the target over the width of the target W, measured along the axis of rotation. The variation of this law that is most frequently used in the field of Human-Computer Interaction is called the "Shannon form", named after the Shannon-Hartley Theorem since the notation below resembles it very closely:

The purpose of this model is in the development of information in the form of "bits per second". This is decidedly an interesting abstraction, since at the time of this form's development little work had been done in quantifying human brain activity using computer science metrics. Interestingly, this particular implementation was originally not conceived as a direct application to the field of computer science but rather psychology, which was an interesting concept and eventually became very easily applied to computer science when it was decided to be applied that way.

Fitts' Law in the field of computer science has been traditionally used for gauging user interface readability with a traditional mouse pointer. However, I believe we can apply Fitts' Law in numerous ways. We can apply Fitts' Law in psychology exams delivered through computer systems to better analyze this information, and we can likely develop additional metrics and more information-rich variation of Fitts' Law once we can analyze this information with much finder granularity.