Effects of limb-specific visual occlusion on bimanual reach-to-grasp coordination in an immersive virtual reality environment.

Introduction: Visual feedback plays an important role in bimanual coordination, but the specific contribution of visual information from each limb during symmetric bimanual reach-to-grasp movements remains unclear. This study examined how selective visual occlusion of one or both hands influences movement coordination in an immersive virtual reality environment. Methods: Nineteen right-handed participants performed symmetric bimanual reach-to-grasp movements under four visual feedback conditions: both hands visible (BV), left hand absent (LA), right hand absent (RA), and both hands absent (BA). Movement initiation, movement termination, movement time, peak velocity, time after peak velocity, path length, lateral trajectory deviation, and grasp success were analyzed. Results: Movement initiation remained synchronized across visual conditions, whereas movement termination, movement time, trajectory characteristics, and grasp success were influenced by selective visual occlusion. Peak velocity showed condition-dependent differences between the hands, while movement time increased primarily for the occluded hand under unilateral visual occlusion. The non-dominant hand consistently exhibited longer path lengths, whereas lateral trajectory deviations depended on the availability of visual feedback. Grasp success was higher for the visible hand during single-hand occlusion. Conclusion: Selective visual occlusion primarily influenced the later stages of bimanual reaching and grasping, while early movement planning remained comparatively robust. These findings demonstrate that limb-specific visual feedback contributes to coordinated bimanual behavior in a movement-phase-dependent manner and highlight the utility of immersive virtual reality for investigating the role of visual information during upper-limb coordination.