No strategic interactions between sequential grasping actions.

Every day we perform consecutive grasping actions to complete our desired goals. Although we have a good understanding about how the brain programs one grasping action towards a single object, we have limited knowledge about how the brain programs a grasping action within the context of a sequential task. The aim of this study was to investigate whether the characteristics of the second object in a sequence of two grasping movements affects how the first object is grasped. In Experiment 1, we explored whether the size and orientation of the second object would affect the grip aperture and grip orientation used to grasp a first cylindrical object that varied between two sizes. Unlike results reported by Hesse and Deubel, the orientation of the second object had no significant influence on the grip orientation used to grasp the first object. However, when the second object was smaller than the first object, participants reached out with a smaller peak grip aperture relative to when the second object was the same size or larger. In Experiment 2 we manipulated object orientation but not size, in a strict replication of Hesse and Deubel's study. Like Experiment 1, we found no effect of the second object's orientation on the first grasping movement. Based on these results, it is suggested that the second object within a sequential task will only interfere with the grasping kinematics towards the first object when both action plans have overlapping features, and most importantly this is not dependent on providing a strategic benefit to the overall movement.