Figure 1. A scatter plot of response time versus index of difficulty.
distance target the movement strategy is to move quickly first and then adjust direction and speed, while for a short distance target, the strategy involves slow movement and direction correction simultaneously. Furthermore, there are two distinctive differences between Fitts' law and the way the user interacts with the mobile device. First, Fitts' law assumes the user interacts with a fixed target, while in this experiment, the mobile device is invariably affected by the movement of the subject. Second, the subject may move the hand-held device and the pen to coordinate the targeting action.
This experiment has provided the user interface designer with useful information about the placement and size of interface controls for pen-based interfaces. Further experimental work on walking speed and target size is required to derive a more comprehensive model of how users interact with these devices for on-the-move applications. Fitts' law can then be modified and applied to a broader domain.
Fitts, P. M.( 1954), "The information capacity of the human motor system in controlling amplitude of movement", Journal of Experimental Psychology, Vol 47, No. 6, pp381-391.
Ren, X. & Moriya, S.( 1997), Selection strategies for small targets and the smallest maximum target size on pen-based systems, IEICE Transactions on Information and Systems, Vol E00-D No 7, 1-6.