Action preparation in grasping reveals generalization of precision between implicit and explicit motor processes

It is often claimed that merely seeing a graspable object can elicit the implicit representation of a potential grasp. But can this representation affect the explicit execution of an actual grasp, and if so, how? In an open-loop paradigm, we instructed participants to grasp small, medium, or large test disks with the appropriate grip configuration (pincer, tripod, or pentapod). Before the presentation of these tests, we presented congruent or incongruent distractors. To assess interactions between implicit (putatively elicited by the distractors) and explicit (actually executed) sensorimotor processes, we measured preview reaction times (as an index of action preparation) and grasp kinematics (as an indicator of sensorimotor representations for motor control). Results indicate that action preparation is indeed affected by the presentation of preceding distractors. However, costs in action preparation were measured only when the first, implicit process was less precise than that of the actual grasp. We suggest that an interaction occurs at the level of sensorimotor processes through a mechanism which generalizes a precision parameter. We interpret these findings in relation to processes involved in real-time motor control and within the framework of theories of motor cognition.