Switching tools: perceptual-motor recalibration to weight changes.

In order to effectively switch between tools, an actor must re-calibrate perceptual-motor control appropriately for the new tool's kinetic properties. This study explored changes in perceptual-motor control in response to switching to a tool of a different weight when performing a complex control task with moving objects. In Experiment 1, 30 participants were each randomly assigned to one of three groups in a baseball batting simulation: a standard group that always used the same bat weight (1.08 kg), a Lighter group that switched from the standard bat to a 0.79 kg bat, and a Heavier group that switched from the standard bat to a 1.36 kg bat. For both the Heavier and Lighter groups, temporal swing errors were significantly larger (as compared to the standard group) in the first block of trials following the bat change. Both groups re-calibrated quickly: within 5-10 trials after the bat change there were no significant difference between the groups. Analysis of swing kinematics indicated that the two change groups used different means for re-calibrating perceptual-motor control: the Lighter group altered swing velocity while the Heavier group altered swing onset time. In Experiment 2, when batters switched from a 0.79 kg bat to a 1.08 kg bat, perceptual-motor calibration depended on the recommended bat weight for each participant (Bahill and Freitas in Ann Biomed Eng 23:436-444, 1995): batters with a heavier recommended weight altered swing velocity while batters with a lower recommended weight altered onset time. The strategy used for perceptual-motor recalibration and time required to re-calibrate in a complex motor task is dependent on the action boundaries of the actor.