Does Precision Grip Research Extend to Unconstrained, Multidigit Grasping?

Abstract

Most daily tasks require using our hands. Whether taking a sip from a glass or throwing a ball, we effortlessly select appropriate grasps. Yet, despite many possible hand configurations, most grasping research has focused on the finger-and-thumb precision grip. We thus questioned whether findings on precision grip hold under unconstrained grasping conditions. To test this, we compared how participants grasped 3D objects made of brass and wood, with both precision grip and unconstrained grasps. When unconstrained, participants rarely selected precision grips, favoring multi-digit grasps. Nevertheless, in both conditions, participants shifted grasps towards the objects center of mass and, when grasp factors conflicted, the variability in their selections increased, indicating greater uncertainty about the optimal strategy. Further, despite favoring multidigit grasps, participants consistently placed the thumb and index finger on the same positions on the objects, suggesting that in multidigit grasps, the additional fingers primarily provided support. Our findings thus reveal that object material affects unconstrained grasping similarly to precision grip and imply that previous precision grip research may extend to unconstrained, multidigit conditions. NEW & NOTEWORTHYMost grasping research focuses on two-digit precision grips, yet humans have more than two fingers. Here, we test whether previous precision grip findings apply to unconstrained grasping. We find that participants often use more than two digits when free to choose but consistently place thumb and index finger similarly on objects regardless of the number of fingers used. Our results thus highlight how the large body of precision grip literature can extend to multidigit grasping.