Effect of Object and Task Properties on Bimanual Transport

ABSTRACT

The use of both hands simultaneously when manipulating objects is fairly commonplace, but it is not known what factors encourage people to use two hands as opposed to one during simple tasks such as transport. In particular, we are interested in three possible transport strategies: unimanual transport, handing off between hands, and symmetric bimanual transport. In this study, we investigate the effect of object size, weight, and starting and ending position (configuration) as well as the need to balance the object on the use of these three strategies in a bowl-moving task. We find that configuration and balance have a strong effect on choice of strategy, and size and weight have a weaker effect. Hand-offs are most often used when the task requires moving an object from left to right and vice versa, while the unimanual strategy was frequently used when passing front to back. The bimanual strategy is only weakly affected by configuration. The need to balance an object causes subjects to favor unimanual and bimanual strategies over the hand-off. In addition, an analysis of transport duration and body rotation suggests that strategy choice may be driven by the desire to minimize body rotation.

Keywords:

• arm movements
• bimanual performance
• grasping
• motion planning

Notes

¹ When grasping, subjects would first move and adjust their fingers on the bowl; then their fingers would stop moving for a moment as the participant braced to take on the load of the bowl. This solidifying of the grasp pose right before lifting was considered the moment a stable grasp is formed.

² These data separate out the two unimanual strategies (L and R) and the two hand-off strategies (LR and RL) and also show raw frequency of each strategy averaged over participants, rather than the predicted probabilities of Figure 2 that account for random variation between participants.