Figure 1 | Scientific Reports

Figure 1

From: Analogous adaptations in speed, impulse and endpoint stiffness when learning a real and virtual insertion task with haptic feedback

Figure 1

Comparable changes in the correlates of motor learning were observed in the real and virtual insertion task. (a) In the real task, the hand was strapped to the end-effector of a robot interface, to which a set of pliers and a metal clip were attached. Participants were instructed to move the hand from the start position and insert the tool into the fixture 120 times. (b) A separate group of participants grasped a robotic interface to insert a virtual tool into a fixture. Haptic feedback of the interaction was provided. (c) The hand’s trajectory in the early phase from two representative participants in the real (black) and virtual insertion (blue). The hand moved relatively straight from the start to the insertion position. (d) Normalized movement duration as a function of trial number in both environments. The duration dropped rapidly in the first few trials, and slowly declined thereafter. (e) Normalized speed increased more rapidly in the first half than in the latter half of the task. The change in the speed was comparable between the real and virtual tasks. (f) Normalized impulse and (g) normalized stiffness, estimated from average normalized muscle activity in the real task and grasp force in the virtual task, both declined as a function of trials in a comparable manner in the real and virtual environments. (h) Normalized force during insertion declined in the real insertion task, but not during virtual insertion. (i) Control experiment revealed that the force needed to insert the tool with the clip decreased with repeated insertion due to the degradation of the fixture.

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