Abstract
When performing a goal-directed action with a tool, it is generally assumed that the point of control of the action system is displaced from the hand to the tool, implying that body and tool function as one system. Studies of how actions with tools are performed have been limited to studying either end-effector kinematics or joint-angle coordination patterns. Because joint-angle coordination patterns affect end-effector kinematics, the current study examined them together, with the aim of revealing how body and tool function as one system. Seated participants made point-to-point movements with their index finger, and with rods of 10, 20, and 30 cm attached to their index finger. Start point and target were presented on a table in front of them, and in half of the conditions a participant displacement compensated for rod length. Results revealed that the kinematics of the rod's tip showed higher peak velocity, longer deceleration time, and more curvature with longer rods. End-effector movements were more curved in the horizontal plane when participants were not displaced. Joint-angle trajectories were similar across rod lengths when participants were displaced, whereas more extreme joint-angles were used with longer rods when participants were not displaced. Furthermore, in every condition the end-effector was stabilized to a similar extent; both variability in joint-angle coordination patterns that affected end-effector position and variability that did not affect end-effector position increased in a similar way vis-à-vis rod length. Moreover, the increase was higher in those conditions, in which participants were not displaced. This suggests that during tool use, body and tool are united in a single system so as to stabilize the end-effector kinematics in a similar way that is independent of tool length. In addition, the properties of the actual trajectory of the end-effector, as well as the actual joint-angles used, depend on the length of the tool and the specifics of the task.
Highlights
A tool in use is “a sort of extension of the hand, almost an attachment to it or a part of the user’s own body” (Gibson, 2015, p. 35)
We studied how the kinematics of the rod’s tip as well as the degree of stabilization of the tip were affected by rod length
We examined how the combination of participant placement and different end-effector lengths was affecting: (1) the trajectory of the tip of the end-effector, (2) joint-angle trajectories, (3) jointangle coordination patterns, and (4) the relationship between end-effector kinematics and joint-angle coordination patterns
Summary
A tool in use is “a sort of extension of the hand, almost an attachment to it or a part of the user’s own body” (Gibson, 2015, p. 35). Others have concentrated on processes underlying tooling kinematics; Van der Steen and Bongers (2011) studied participants who were making pointto-point movements with the tip of a small rod attached to the index finger They showed that the joint-angle coordination patterns in the arm stabilized the rod’s tip and the hand to a similar extent. The current paper has investigated how endeffector kinematics and the stabilizing properties of joint-angle coordination patterns are affected by tool length in order to advance our understanding of how body and tool function as one system This was done by studying able-bodied participants making point-to-point movements with rods of varying lengths attached to the index finger. We expected that GEV would increase in these conditions to ensure stabilization of the tip of the tool (cf. Greve et al, 2015), which would reflect a way in which body and tool function as one system
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
