A Web-based Test of Fitts' Law

Right now you are sitting at a computer.  Your back and eyes may be straining in subtle ways.  Let's face it, do you really sit up straight like your mother always told you to?  


Ergonomics , also know as Human Factors, is the study of human capabilities in relationship to work demands.  This area is being studied in order to improve human performance, and provide a more comfortable work atmosphere.  We no longer try to fit the human to the machine, but the machine to the human.  These studies not only apply to things like furniture and hardware; now these ergonomic guidelines are being applied in web development, finding the best sizes and locations for every detail of the webpages you see online.

Fitts' Experiment
In 1954 a psychologist named Paul Fitts of Ohio State University and later the University of Michigan developed a model of human movement based on rapid, aimed movement.  It makes sense that response time would be affected by the distance moved and the precision demanded by the size of the target to which one is moving.  To investigate this relationship Fitts conducted experiments in which target distance and width were varied.

Reciprocal Tapping
In this experiment, subjects were asked to tap a stylus back and forth between two metal plates while their time was recorded.  If they tapped a side plate instead of the target center plate an error was recorded.  The subjects were also told to emphasize accuracy rather than speed.

More About Fitts' Law


Research Publications

  1. Fitts, P. M. (1954). The information capacity of the human motor system in   controlling the amplitude of movement. Journal of Experimental Psychology, 47, 381-391.

  2. Welford, A. T. (1968). Fundamentals of Skill. London: Methuen.

  3. MacKenzie, I. S. (1989).  A note on the information-theoretic basis for Fitts' law.  Journal of Motor Behavior, 21, 323-330.

  4. Mackenzie, I. S. Fitts' Law as a Performance Model in Human-Computer Interaction. PhD thesis, University of Toronto, 1991.

  5. MacKenzie, I. S. and Buxton, W. Extending Fitts' Law to Two-Dimensional Tasks. In CHI '92 Conference of Human Factors in Computing Systems, 1992, pp. 219-226.
    Summary:  Fitts' Law is designed for motion in one dimension only.  However, most practical applications of human movement involve motion in at least two dimensions. With rectangle shaped targets, D is still the distance to the center of the target, but it is unclear what to use for W.  If the approach angle creates a vector parallel to one of the sides, it is simple to choose the value for W.  However, if this is not the case, there are four other models to consider: W+H, W*H, SMALLER-OF, and W'.   The W+H and W*H models did not have significantly better correlations than the STATUS QUO model.  The SMALLER-OF model chooses the smaller of the two dimensions to use as W, indicating the accuracy demands of the task.   W' uses the width of the target along an approach vector, retaining the one dimensionality of the model.  When comparing these models with the STATUS QUO  model, the correlations of the SMALLER-OF and W' models did not differ significantly from eachother, but each had a higher correlation than the STATUS QUO model.
  1. MacKenzie IS. Movement time prediction in human-computer interfaces.  [Conference Paper] Proceedings. Graphics Interface '92. Canadian Inf. Process. Soc. 1992, pp.140-50.  Toronto, Ont., Canada.

  1. MacKenzie, I. S., & Buxton, W. (1994). The prediction of pointing and dragging times in graphical user interfaces. Interacting with Computers, 6, 213-227.

  2. Accot, J., & Zhai, S. (1997). Beyond Fitts' law: Models for trajectory-based HCI tasks. Proceedings of the CHI '97 Conference on Human Factors in Computing Systems, New York: ACM, pp. 295-302.

  3. Peter Oel, Paul Schmidt & Alfred Schmitt(2001). Time Prediction of Mouse-based Cursor movements. AFIHM-BCS Conference on Human-Computer Interaction IHM-HCI'2001. Lille, France, Sept. 10-14, 2001. Volume II, 37-40

    Summary: Fitts' Law is widely used as a predictor for movement time of mouse based cursor transfers between objects in a graphical user interface. However, Fitts' Law does not provide an accurate representation for low values of I nor for small target areas.  This paper proposes a new power model that describes movement time within classes of different Ws.  The best fit model is represented by MT=h(w)Dk(w).  h(W) and k(W) are replaced by regression models that best fit the experimental data.  The final power law is given by MT=(aWb)Dc+dlog2(W)

  4. More Fitts' Law Resources: http://www.yorku.ca/mack/RN-Fitts_bib.htm