Effect of Dyadic Haptic Collaboration on Ankle Motor Learning and Task Performance

Abstract

Optimizing skill acquisition during novel motor tasks and regaining lost motor functions have been the interest of many researchers over the past few decades. One approach shown to accelerate motor learning involves haptically coupling two individuals through robotic interfaces. Studies have shown that an individual's solo performance during upper-limb tracking tasks may improve after haptically-coupled training with a partner. In this study, our goal was to investigate whether these findings can be translated to lower-limb motor tasks, more specifically, during an ankle position tracking task. Using one-degreeof-freedom ankle movements, pairs of participants (i.e., dyads) tracked target trajectories independently. Participants alternated between tracking trials with and without haptic coupling, achieved by rendering a virtual spring between two ankle rehabilitation robots. In our analysis, we compared changes in task performance across trials while training with and without haptic coupling. The tracking performance of both individuals (i.e., dyadic task performance) improved during haptic coupling, which was likely due to averaging of random errors of the dyadic pair during tracking. However, we found that dyadic haptic coupling did not lead to faster individual learning for the tracking task. These results suggest that haptic coupling between unimpaired individuals may not be an effective method of This paragraph of the first footnote will contain the date on which you submitted your paper for review.

Haptic Human-Human Interaction During an Ankle Tracking Task: Effects of Virtual Connection Stiffness

“…1A). (1) In blocks with soft connections, the stiffness (K virt ) and damping (C virt ) were set to 20 Nm/rad and 2 Nm•s/rad, respectively, consistent with our previous study [12]. (2) In blocks with hard connections, the stiffness and damping were set to 200 Nm/rad and 6.3 Nm•s/rad, respectively.…”

“…Simulating the connection as a system of springs in series suggested that improvements in tracking could be explained by the averaging of random errors within each dyad, depending on the stiffness of the connection and the relative ankle stiffness of each partner. One potential explanation for these results is the relatively soft stiffness of the connection used in our previous work [12], possibly limiting the communication of tracking goals as described by Takagi et al [5].…”

“…These time and phase shifts prevented memorization of the target trajectory [3]. Consistent with our previous study [12], the amplitude and frequency of the three multi-sine components were chosen to emulate ankle kinematics during healthy gait [16]. In each trial, participants tracked the target trajectory for 26 seconds, then rested for 10 seconds.…”

“…Therefore, the goal of our study was to investigate the effects of virtual stiffness on task performance during a 1-DoF ankle tracking task with and without random noise added to a visually-displayed target. Based on similarities between upper-and lower-limb tracking in our initial findings [12], we hypothesized that dyadic improvements increase with connection stiffness, benefiting the worse partner in the dyad, and that these improvements are explained by the averaging of random errors across partners. We also expected that less correlated tracking errors across partners would correspond to greater improvements due to a larger amount of random error corrected by an elastic connection.…”

“…It remains unclear whether changes in task performance and individual learning obtained for upper-limb movements can be generalized to the lower limb, given differences in physiology and functional tasks in which each are involved [10], [11]. As a first study in healthy individuals, our group investigated a 1-DoF ankle motor task, comparing changes in tracking performance in response to compliant haptic connections with a partner [12]. Our results showed no difference in shortterm, individual learning when training alone or with a partner.…”