Abstract: Background: Practicing arm and gait movements with robotic assistance after neurologic injury can help patients
improve their movement ability, but patients sometimes reduce their effort during training in response to the
assistance. Reduced effort has been hypothesized to diminish clinical outcomes of robotic training. To better
understand patient slacking, we studied the role of visual distraction and auditory feedback in modulating patient
effort during a common robot-assisted tracking task.
Methods: Fourteen participants with chronic left hemiparesis from stroke, five control participants with chronic
right hemiparesis and fourteen non-impaired healthy control participants, tracked a visual target with their arms
while receiving adaptive assistance from a robotic arm exoskeleton. We compared four practice conditions: the
baseline tracking task alone; tracking while also performing a visual distracter task; tracking with the visual
distracter and sound feedback; and tracking with sound feedback. For the distracter task, symbols were randomly
displayed in the corners of the computer screen, and the participants were instructed to click a mouse button when
a target symbol appeared. The sound feedback consisted of a repeating beep, with the frequency of repetition
made to increase with increasing tracking error.
Results: Participants with stroke halved their effort and doubled their tracking error when performing the visual
distracter task with their left hemiparetic arm. With sound feedback, however, these participants increased their
effort and decreased their tracking error close to their baseline levels, while also performing the distracter task
successfully. These effects were significantly smaller for the participants who used their non-paretic arm and for
the participants without stroke.
Conclusions: Visual distraction decreased participants effort during a standard robot-assisted movement training
task. This effect was greater for the hemiparetic arm, suggesting that the increased demands associated with
controlling an affected arm make the motor system more prone to slack when distracted. Providing an alternate
sensory channel for feedback, i.e., auditory feedback of tracking error, enabled the participants to simultaneously
perform the tracking task and distracter task effectively. Thus, incorporating real-time auditory feedback of
performance errors might improve clinical outcomes of robotic therapy systems.