Abstract
Stereopsis is important for prehension. In particular, the end-phase of the reach and initial-phase of the grip that rely on 3D information, visual feedback and online movement correction. This study compared prehension movement kinematics for binocular and monocular viewing between 1) stereo-typical and stereo-anomalous and 2) people with long-term and recent stereo-loss. We recorded movement during a prehension task where participants were instructed to “pick-up a peg and place it in the appropriate slot”. From the movement traces, we extracted six kinematic parameters: peak velocity (PV), maximum grip aperture (MGA), time to maximum grip aperture (tMGA), grip closure time (GCT), deceleration and peg placement time (PPT), which represent movement aspects that rely on different spatial and temporal information. We compared data from “stereo-typical” (n=8) and “stereo-anomalous” (n=13) participants, and we also compared data from people with “long-term stereo-loss” to data collected from people with “recent stereo-loss” (n=10) due to age-related macular degeneration (Verghese et al., 2016). Binocular viewing (compared to monocular) resulted in faster reach and more appropriate grasp for the stereo-anomalous group (all variables p<0.01, except PV) and faster deceleration and PPT in the stereo-typical group (both variables p=0.008). However, the only significant difference between the two groups was for tMGA under monocular viewing (p=0.038). Additionally, binocular viewing for the recent stereo-loss group resulted in a more accurate (MGA p=0.008) and timely grip (GCT p=0.036). More importantly, compared to the long-term stereo-loss group, they performed better in tMGA (p=0.036), deceleration (p<0.001) and PPT (p<0.05) in both viewing conditions (except tMGA binocular) — revealing a stereovision experience benefit. Our data support the claim that a lack of binocularity has detrimental effects on the temporal aspects of the grip (Niechwiej-Szwedo et al., 2011). Furthermore, the experience of stereovision provides an advantage in prehension kinematics well beyond the loss of stereopsis.