Multiple object handling: strategies for cumulative grasping and transport with a single hand

Humans can cumulatively grasp multiple objects and then transport them using a single hand (e.g., when clearing up tableware). This skill, which we refer to as ‘multiple object handling’, helps minimise the number of actions required to transport objects. However, it also presents unique challenges for the sensorimotor system, including the use of grips other than finger-thumb opposition (which is almost always used for grasping single objects). In the present work we explored the strategies used for multiple object handling, particularly focussing on object selection and grip choice. Participants were presented with pairs of objects, asked to grasp one of them and then, without placing that object down, grasp the second object and transport both to a designated location. We examined the order in which participants selected objects, as well as the grips used for grasping and holding them, enabling us to describe a typical approach to multiple object handling. When two objects are grasped cumulatively for transport, finger-thumb opposition is almost always used to grasp the first object, which is then frequently held using an atypical grip (e.g., finger-finger or finger-palm opposition). Finger-thumb opposition can then be used once again to grasp a subsequent object. Grasping objects that are smaller or with lower surface area first may facilitate this approach. This work provides insight into a technique commonly used for efficient object transport. Furthermore, it highlights how an extensive range of atypical grips can be used by humans, broadening understanding of our capacity for dextrous motor control.