Investigating the role of binocular vision in visuomotor control during the reciprocal Fitts's tapping task

Vision provides critical sensory information for the planning and control of goal-directed actions. Relative to monocular viewing, binocular viewing results in superior speed, accuracy, and precision of upper-limb movements, indicating that binocular input facilitates movement planning and execution. Although the contribution of binocular vision to discrete actions is well established, its role in reciprocal movements remains poorly understood. Reciprocal tapping movements (i.e., Fitts' task) provide a useful model for examining movement execution because they place relatively lower demands on motor planning. Moreover, varying the index of difficulty (ID) alters the balance between feedforward and feedback control, with greater ID increasing reliance on feedback. If binocular vision enhances the processing of visual information used for online movement regulation, its benefits should be particularly evident under these more demanding conditions. Accordingly, it was hypothesized that a binocular advantage would be observed during reciprocal actions and would be most pronounced at higher levels of task difficulty. Thirty-four adults with normal vision performed a reciprocal Fitts' tapping task at six ID levels under binocular and monocular viewing conditions, while eye tracking and a motion capture system were used to record movement kinematics. Participants were additionally tested using a discrete pointing task. Consistent with the literature, a significant binocular advantage was found for discrete movements, which was evident in the final deceleration (homing) phase. For the reciprocal task, a reliable binocular advantage emerged earlier during the deceleration phase specifically at ID 3.5 and ID 4.24 while no significant differences were found at ID 5.41 or ID 6.97. In addition, dwell time (i.e., time spent on the target before reversing direction and initiating the next movement) was shorter during binocular viewing at high task IDs. Eye-hand coordination analysis revealed that hand movement initiation preceded eye movement initiation during reciprocal actions, and binocular viewing was associated with a shorter eye-hand delay at ID 3.5 and 4.24. These findings demonstrate that binocular vision plays an important role in movement execution and highlight its multifaceted contribution to sensorimotor control, supporting both the monitoring of limb motion during movement and the visual guidance required for accurate target acquisition.