Subsequent actions influence motor control parameters of a current grasping action

When humans perform a simple grasping movement (e.g., when they pick-up a bottle) in different task contexts (e.g., with the intention to place the bottle at another location or to pour water into a glass), the respective grasping movement is adapted on-line to the task requirements and executed in a fast, precise and smooth way. We investigated whether and how different types of after-grasp movements affected the planning and execution of the same initial grasping segment. If future actions are anticipated and integrated into the execution of an ongoing movement, then parameters of the initial grasping movement should be altered dependent on requirements of the subsequent after-grasp movement. Results indeed showed a strong impact of the after-grasp movement on initial grasping. Participants adopted their grip position to the goal position of the after-grasp movement. Additionally, temporal parameters (such as movement time, timing of peak velocity, acceleration and deceleration) were affected by the after-grasp movement type. These results indicate that parameters of the after-grasp movement were anticipated already at an early motor planning stage. Possible implications on robot control are discussed.