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.
Typical visual displays cover only a fraction of the visual field. How do such restrictions influence the perception of visual speed during self-motion? While surrounded by a panoramic screen on which an alley of terraced houses was presented, participants walked at constant speed on a treadmill. They adjusted the speed of the visual scene to match their subjectively experienced walking speed. We manipulated which areas of the visual field remained visible. Only this effective Field of View (FoV) contributed to stimulation by scene motion, while the remainder of the scene was replaced by a homogenous grey overlay with no optic flow. We found that the central part of the visual field needs to be presented substantially faster than the actual walking speed to be perceived as matching. This ratio of visual to actual walking speed (“gain”) is lower for equally sized parts of the visual periphery. This result is mainly explained by motion-energy density, but there are also unique contributions of size and position in the visual field (including interaction of the three). There is substantial inter-individual variability in the overall gain perceived as optimal, which is in part explained by step length, but shows no relation to anthropometric measures (body height, leg length). Our results quantify the contribution of different visual field areas to motion perception in complex scenes and are of specific relevance for simulating self-motion, especially in virtual-reality setups with limited horizontal FoV.
Prolonged exposure (adaptation) to blur, flicker or motion can transiently enhance visual acuity (VA). Such improvement could be linked to decreased contrast sensitivity (CS) for low spatial frequency (SF) image structure. Here, we determine if and why low SFs are required for such acuity improvement following adaptation. We measured CS using SF band-pass filtered optotypes with and without adaptation. We also measured CS for these stimuli in the presence of a SF low-pass fixed-contrast “pedestal”. Adaptation to receding motion improves VA for conventional but not vanishing optotypes (which contain little low SF structure), indicating a crucial role for low SFs. Adaptation reduces CS at all SFs (particularly for the lowest SF). In unadapted observers - interestingly, however, CS for higher SF information is always enhanced/facilitated by a low SF pedestal. Therefore, any adaptation-driven suppression of low SFs must improve the discriminability (rather than detection) of high SFs to improve recognition. Using a simple filter-combination model, we show that recognition must be operating on information that has been combined across SFs.
