Visual feedback improves bimanual force control performances at planning and execution levels

Abstract

The purpose of this study was to determine the effect of different visual conditions and targeted force levels on bilateral motor synergies and bimanual force control performances. Fourteen healthy young participants performed bimanual isometric force control tasks by extending their wrists and fingers under two visual feedback conditions (i.e., vision and no-vision) and three targeted force levels (i.e., 5%, 25%, and 50% of maximum voluntary contraction: MVC). To estimate bilateral motor synergies across multiple trials, we calculated the proportion of good variability relative to bad variability using an uncontrolled manifold analysis. To assess bimanual force control performances within a trial, we used the accuracy, variability, and regularity of total forces produced by two hands. Further, analysis included correlation coefficients between forces from the left and right hands. In addition, we examined the correlations between altered bilateral motor synergies and force control performances from no-vision to vision conditions for each targeted force level. Importantly, our findings revealed that the presence of visual feedback increased bilateral motor synergies across multiple trials significantly with a reduction of bad variability as well as improved bimanual force control performances within a trial based on higher force accuracy, lower force variability, less force regularity, and decreased correlation coefficients between hands. Further, we found two significant correlations in (a) increased bilateral motor synergy versus higher force accuracy at 5% of MVC and (b) increased bilateral motor synergy versus lower force variability at 50% of MVC. Together, these results suggested that visual feedback effectively improved both synergetic coordination behaviors across multiple trials and stability of task performance within a trial across various submaximal force levels.

Higher visual gain contributions to bilateral motor synergies and force control

“…Moreover, our correlation findings indicated that a decrease in V ORT across multiple trials with higher visual gain conditions was significantly related to less force error within a trial. These findings expand prior results in that bilateral motor synergies across multiple trials from no vision to vision conditions were associated with improved bimanual force control within a trial 34 . Improved bilateral force control strategies with increased visual gain is typically observed when a surgeon is performing an operation using microscopic surgery techniques 47 , 48 .…”

“…To stabilize task performances (i.e., greater V Index ), the motor system may select one of three strategies: (a) increased flexibility (higher V UCM ) of elemental variables without changes in stability (V ORT ), (b) increased stability (lower V ORT ) of elemental variables without changes in flexibility (V UCM ), and (c) increased both flexibility (higher V UCM ) of elemental variables and stability (lower V UCM ). Our recent findings revealed that the presence of visual feedback using two visual gain conditions (i.e., 13 pixels/N at 5% of MVC and 8 pixels/N at 25% and 50% of MVC) improved bilateral motor synergies with decreased bad variance as compared with no vision condition 34 . These findings suggested that the availability of visual information during bimanual force control may facilitate the motor system to increase the stability patterns (i.e., a reduction of bad variance) across multiple trials stabilizing task performances.…”

“…Vision influenced the non-motor equivalent components in a four-fingers force control task and V Index in a bimanual index finger force control task as compared with no vision 17 , 32 , 33 . Moreover, recent UCM findings indicated that V Index during bimanual force control tasks increased from no vision to vision conditions, and the improved V Index values were related to a reduction of force error and variability within a trial 34 . Beyond these identified vision and no vision effects, potential changes in bilateral motor synergies are still unknown across multiple trials that vary by visual gain.…”

Examining the Alignment between Subjective Effort and Objective Force Production

“…Current research argues that force accuracy between intended and actual force can be increased by visual feedback 65 . We deliberately did not use visual feedback in the present experiment for two reasons.…”