Don't spill my beer: A comparison of reach trajectories between grasping and pointing to two potential target objects


Simple pointing/reaching tasks are used to understand how the brain plans movements. Often, reaching movements are used to transport the hand to grasp an object. Grasping requires more task demands and affordances. For instance, the need to grasp with the palm as opposed to the back of the hand requires the limb to orient the palm to the object whereas pointing has no such constraint. The purpose of the study was to compare the limb transport strategies used between pointing and grasping to an uncertain target location. Participants initiated a reaching movement to two cylinders placed horizontally in front of them, only on movement initiation was one of the cylinders cued as the target object. Previous work in 'go-before-you-know' tasks using pointing suggests participants plan a movement between the two target locations to increase the chance of success once the target is cued. When grasping it is not clear what the participant will prioritize. When reaching with the right hand, if participants prioritize having the palm available to both objects they should veer to the right side. If they prioritize reaching to the object most available to their palm, they will veer to the left, but a corrective movement may cause them to hit the right object with the back of their hand (hence 'spilling the beer'). The results will be able to identify whether different biomechanical constraints and the risk of conflicting non-target objects associated with grasping lead to different reach trajectories compared to a simple pointing task.