Fitts’ Law: Improving Human Movement
26 Mar 2008
Fitts’ Law: Improving Human Movement
I chose Paul Fitts’ Information Capacity of Human Motor Systems in Controlling the Amplitude of Movement because I discovered Fitts’ Law in Jensen Harris blog post about the new user interface for Microsoft Office 2007. Jensen was explaining how Microsoft was using Fitts’ Law to make Microsoft Office 2007 easier to use. Fitts’ Law basically states that the speed of movement is a function of the size of the destination and the distance from the current position. Later research has proved that Fitts’ Law applies to computers, especially when using a mouse to click on a button. Jensen explained in the blog post that the "Mini Toolbar" was created to sharply decrease the distance from the cursor to commonly used formatting commands, especially with large monitors.
However Paul Fitts did his work long before computer mice were created in 1954, on a contract with the Air Force. The article was originally printed in the Journal of Experimental Psychology, 47, 381-391. His research was conducted in 3 experiments. The first one instructed a collage-aged subject using a stylus to touch an area on one side of the table and then the other as fast as the subject could. The experiment varied the size of the "goal" area and the distance between the two. Another experiment asked the subject to move rings from one peg to another. The experiment varied the difference between the size of the peg and the hole in the disk as well as the distance between pegs. A final experiment asked subjects to move pegs from one rack to another. The experiment varied the tolerance between the size of the hole and the size of the peg as well as the distance between the racks of pegs.
Fitts found that "the rate of performance for all tasks studied increased uniformly as movement amplitude was decreased and as tolerance limits were extended" ([Reprint] 266). Fitts also found that movements become difficult when there was a low tolerance and that movement was inefficient with a large tolerance and small amplitude. I would agree with his results and I believe that they make common sense.
As mentioned earlier, the results also match the user experience on a computer using a mouse of touch screen (Jensen).
Fitts’ report was only the beginning of research. Many researchers have worked on and extended his ideas (Jensen). Thus the original report written by Fitts does not provide a comprehensive introduction to Fitts’ Law which has been subsequently far more extensively researched. However Fitts’ research must have been convincing, since many people have worked on and built upon it.
Fitts’ goal was to investigate human motor skills under an Air Force contract. He was looking for a unified theory of motor capacity related to information gathered. I felt that he did not clearly explain how information was related to movement. He invented an index of difficulty and formula to create it. I however, do not see what the index of difficulty is trying to show. Also how does "information" relate to movement? I think that the information component should have been better explained or left out completely and the report should have focused on the time component.
I do not think that Fitts was biased or even could have been. Who has anything to gain by slanting research about human motor skills?
After reading Fitts’ report I am wondering about how the information component affects results or even how that could be tested. I am also wondering what his index of difficulty explains.
Fitts states that his research was unique because it attempted to find a unifying theory reconciling the amplitude, duration, and variability of movements (262). He did this by proposing a formula which takes into account all of these factors.
This is a scholarly report because it is terse and does not clearly summarize the importance of this new research. Also it is published in a scholarly journal and lays out the experiments in detail.
Fitts cited 25 sources in his paper. The majority of the sources were other scholarly papers printed in similar journals.
Fitts’ report broke new ground in 1954 by creating a unified theory reconciling the amplitude, duration, and variability of movements of the human motor system. His research was later built upon and confirmed by many substituent researchers. His law has been proven to be very important in the computer industry since it also applies to moving a mouse along the screen. Fitts’ Law was used in creating Microsoft Office 2007 to make buttons easier to hit.
- Harris, Jensen. "Giving You Fitts." Jensen Harris: An Office User Interface Blog. 22 Aug 2006. Microsoft. 25 Mar 2008 <http://blogs.msdn.com/jensenh/archive/2006/08/22/711808.aspx>.
- Fitts, Paul M. "Information Capacity of Human Motor Systems in Controlling the Amplitude of Movement." Journal of Experimental Psychology. 47 (1954) 381-391.