Multiple object handling: exploring strategies for cumulative grasping and transport using 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 (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 and the grips used for grasping and holding them. Results provide preliminary evidence for a typical approach to multiple object handling. We observed that when two objects were grasped cumulatively for transport, finger-thumb opposition was almost always used to grasp the first object, which was then frequently held using an atypical grip (e.g., finger-finger or finger-palm opposition). Finger-thumb opposition was almost always used once again to grasp the subsequent object. Participants preferred to grasp objects with lower mass or surface area first, potentially facilitating this approach. In sum, this work provides insight into a technique commonly used for efficient object transport.