Finger width corrections in Fitts' law: implications for speed-accuracy research

This note points out that using the finger as a test probe in a Fitts task may lead to misleading results, because of the increased target tolerance resulting from the width of the finger pad. An experiment demonstrates the need to use a corrected target width when calculating the index of difficulty; without this correction, information processing rates are overestimated. An example is given of a developmental study in which the finger pad size changes with age. The resulting changes in the calculated rates of information processing are shown to be markedly different for the different age groups.