ACCURACY AND VARIABILITY OF THE MOVEMENT IN FITTS AND SCHMIDTS LAWS

In Schmidt's experiments, only properties of actually produced movemen ts systems are measured; in Fitts' experiments, external task paramete rs are measured too (target size and distance). Thus, the laws contain variables of different natures and cannot be reduced to each other ev en formally. These difference especially reveals itself in modeling: a model of variability can be simpler if it deals with the performance variables only. On the other hand, modeling Fitts' law, one should tak e into account not only the human effector system but features of the experimental apparatus as well. These differences have not been suffic iently reflected in Plamondon & Alimi's target article.