Abstract
Prior to initiating a grasping action, the nervous system generates a motor plan aimed at optimizing task performance. Despite extensive research on single target grasping, the mechanisms by which grasping movements are planned in the context of multiple potential targets, referred to as target uncertainty, remain poorly understood. The present study investigated how the nervous system concurrently plans multiple grasping movements for potential targets with conflicting size characteristics. Using 3D motion capture to measure hand kinematics, participants were presented with two cylindrical objects of different sizes and were required to grasp one of them under two distinct conditions. In the Go-Before-You-Know condition, participants initiated their grasping movement before knowing which object would be the target. In contrast, in the Know-Before-You-Go condition, the target object was identified prior to movement onset. Results revealed that, under target uncertainty, peak grip aperture increased when the distractor object was larger than the target but was not significantly influenced when the distractor was smaller than the target. These findings suggest that the nervous system engages in parallel motor planning for multiple potential actions and tends to scale the grip toward the largest possible target. This behaviour appears to represent an adaptive strategy in which the motor system proactively scales the grasp to accommodate the largest potential target within the action space. This approach likely serves to optimize the efficiency and reliability of executing a successful grasping action.
