Selection criteria for preparatory object rotation in manual lifting actions.

Participants lifted a canister by its handle while balancing a ball on the lid. Experiment 1 allowed object rotation prior to lifting. A lifting comfort zone was measured by the variability in object orientation at lift; its size depended on the object mass and required task precision. The amount of prelift rotation correlated with the resulting change in lifting capability, as measured for different object orientations. Experiment 2 required direct grasping without preparatory rotation. Task completion time and success rate decreased, and initial object orientation affected prelift time. Results suggest that lifting from the comfort zone produces more robust performance at a cost of slower completion; moreover, physical rotation could be replaced by mental planning when direct grasping is enforced.