The dynamics of human isometric pointing movements under varying accuracy requirements

The goal of the present study was to explore the relation between speed-acc uracy trade-off phenomena and action kinematics in the case of pointing und er isometric conditions. Increasing task difficulty resulted in a linear in crease in movement time las predicted by Fitts' law) and in systematic chan ges in the spatio-temporal patterning of force production. The observed cha nges in motion topology were similar to those reported for isotonic tasks a nd adequately captured by a limit cycle model derived for the latter type o f task. These results indicate that, for isometric force control as for iso tonic position control, the reasons underlying the emergence of Fitts' law might be sought in dynamic trajectory formation processes. (C) 2000 Elsevie r Science Ireland Ltd. All rights reserved.