Discrimination of visual-proprioceptive trajectories during passive movements with muscle vibration


In a previous study (Alexander et al. SCAPPS 2019), we examined how the addition of proprioceptive noise impacted the perceived trajectory of reaching movements. We asked participants to perform rapid reaching movements to self-selected directions and judge whether a visual cursor, representing fingertip position, was rotated clockwise or counterclockwise with respect to their actual reach. We used simultaneous biceps-triceps tendon vibration during the movement to implement proprioceptive noise. Surprisingly, we found that participants' discrimination sensitivity (JND) consistently improved when reaching with concurrent vibration compared to without vibration (mean difference -8.72°, 95% CI [-11.48, -5.05]). We proposed that the presence of proprioceptive noise may have increased the weight given to the visual prediction associated with the reaching movements and its comparison with the visual feedback, resulting in improvement of trajectory discrimination. Based on this logic, we hypothesized that the removal of the active sensorimotor prediction during passive movements would remove the facilitating effects of movement vibration observed previously. To test this, participants (n=16) grasped a motorized hand platform that moved their hand passively through random trajectories. They were required to judge if visual feedback was rotated with respect to the trajectory, performing the discrimination task with concurrent vibration and without vibration. Estimates of JND showed that the passive discrimination was not affected by vibration (mean difference 1.15° [-1.42, 3.73]). Taken together, our results support the hypothesis that the comparison of visual feedback with a forward visual sensorimotor prediction leads to improved visual discrimination.

Acknowledgments: Supported by Natural Sciences and Engineering Research Council of Canada