Modeling One-Dimensional Touch Pointing with Nominal Target Width

Yu-Jung Ko, HANG ZHAO, I. Ramakrishnan, Shumin Zhai, Xiaojun Bi

Abstract: Finger-Fitts law [6] is a variant of Fitts' law which accounts for the finger ambiguity in touch pointing. It involves the effective target width $W_e$ (i.e., $\sqrt{2 \pi e}\sigma$) in modeling touch pointing. We hypothesize that the nominal target width ($W$) can be used in lieu of $W_e$ in Finger-Fitts law. Such a model, called Finger-Fitts-$W$ model, complements the original Finger-Fitts law because it suits the situation where the distribution of endpoints is unknown, such as answering the following question without running a study: "what would be the target selection time if the target size increases from 2 to 3 cm?". Although the Finger-Fitts-$W$ model has been implied, it is under-studied. In this short paper, we compare using nominal width ($W$) vs. effective width ($W_e$) in one-dimensional touch modeling. The results showed that the Finger-Fitts-$W$ model improves the model fitness over the conventional Fitts' law and has a slight improvement over the original Finger-Fitts law. Our key takeaway is that Finger-Fitts-$W$ is a valid model for predicting touch pointing movement time. It complements the original Finger-Fitts law as it can predict movement time of touch pointing even if the distribution of endpoints is unknown.

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