Abstract
Evidence suggests that the sense of the position of our body parts can be surreptitiously deceived, for instance through illusory visual inputs. However, whether altered visual feedback during limb movement can induce substantial unconscious motor and muscular adjustments is not known. To address this question, we covertly manipulated virtual body movements in immersive virtual reality. Participants were instructed to flex their elbow to 90° while tensing an elastic band, as their virtual arm reproduced the same, a reduced (75°), or an amplified (105°) movement. We recorded muscle activity using electromyography, and assessed body ownership, agency and proprioception of the arm. Our results not only show that participants compensated for the avatar’s manipulated arm movement while being completely unaware of it, but also that it is possible to induce unconscious motor adaptations requiring significant changes in muscular activity. Altered visual feedback through body ownership illusions can influence motor performance in a process that bypasses awareness.
Highlights
Evidence suggests that the sense of the position of our body parts can be surreptitiously deceived, for instance through illusory visual inputs
As we observed for the arm movement amplitudes, the altered visual feedback led to significantly different magnitudes of the real arm’s muscular activity, as shown by the index of the EMG peaks (F(2,46) = 4.80; Greenhouse-Geisser www.nature.com/scientificreports (G-G) corrected p = 0.022; η2 = 0.17), especially between the conditions “C 15°” and the “C −15°”, with the latter inducing stronger muscular activations (EMG peaks: “C 15°” vs. “C −15°”: p = 0.001)
In the condition in which the avatar’s arm range of movement was increased (“15°”) the EMG peaks were on average smaller than the ones reported in the condition where the avatar’s arm had no drift (“C 15°” vs. “C 0°”: p = 0.087). These results were confirmed by the index of the overall muscular activity (i.e. EMG areas) for which a large effect of condition was found (F(2,46) = 9.70; p < 0.001, η2 = 0.30); post-hoc tests revealed significantly stronger muscular activity in the “C 0°” and “C-15°” conditions compared to the “C 15°” one
Summary
Evidence suggests that the sense of the position of our body parts can be surreptitiously deceived, for instance through illusory visual inputs. Whether altered visual feedback during limb movement can induce substantial unconscious motor and muscular adjustments is not known To address this question, we covertly manipulated virtual body movements in immersive virtual reality. The authors found that during active displacement, the location of the hand indicated by the participants was closer to the position indicated on the screen, while in the passive condition, the location indicated by participants was closer to the real hand location[9] These studies suggest that vision predominates over proprioception in limb localization tasks, and that the reliance on altered visual input can increase the error in limb position estimation. Our final aim was to see whether significant changes in motor behavior of participants could go unnoticed
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