Melmoth Dean R, Finlay Alison L, Morgan Michael J, Grant Simon
Department of Optometry and Visual Science, City University, London, United Kingdom.
Invest Ophthalmol Vis Sci. 2009 Aug;50(8):3711-20. doi: 10.1167/iovs.08-3229. Epub 2009 Apr 1.
To examine the effects of permanent versus brief reductions in binocular stereo vision on reaching and grasping (prehension) skills.
The first experiment compared prehension proficiency in 20 normal and 20 adults with long-term stereo-deficiency (10 with coarse and 10 with undetectable disparity sensitivities) when using binocular vision or just the dominant or nondominant eye. The second experiment examined effects of temporarily mimicking similar stereoacuity losses in normal adults, by placing defocusing low- or high-plus lenses over one eye, compared with their control (neutral lens) binocular performance. Kinematic and error measures of prehension planning and execution were quantified from movements of the subjects' preferred hand recorded while they reached, precision-grasped, and lifted cylindrical objects (two sizes, four locations) on 40 to 48 trials under each viewing condition.
Performance was faster and more accurate with normal compared with reduced binocular vision and least accomplished under monocular conditions. Movement durations were extended (up to approximately 100 ms) whenever normal stereo vision was permanently (ANOVA P < 0.05) or briefly (ANOVA P < 0.001) reduced, with a doubling of error rates in executing the grasp (ANOVA P < 0.001). Binocular deficits in reaching occurred during its end phase (prolonged final approach, more velocity corrections, poorer coordination with object contact) and generally increased with the existing loss of disparity sensitivity. Binocular grasping was more uniformly impaired by stereoacuity loss and influenced by its duration. Adults with long-term stereo-deficiency showed increased variability in digit placement at initial object contact, and they adapted by prolonging (by approximately 25%) the time spent subsequently applying their grasp (ANOVA P < 0.001). Brief stereoreductions caused systematic shifts in initial digit placement and two to three times more postcontact adjustments in grip position (ANOVA P < 0.01).
High-grade binocular stereo vision is essential for skilled precision grasping. Reduced disparity sensitivity results in inaccurate grasp-point selection and greater reliance on nonvisual (somesthetic) information from object contact to control grip stability.
研究双眼立体视觉的永久性降低与短暂降低对伸手和抓握（prehensile）技能的影响。
第一个实验比较了20名正常成年人和20名长期存在立体视觉缺陷的成年人（10名具有粗略立体视觉缺陷，10名具有无法检测到的视差敏感度）在使用双眼视觉、仅使用优势眼或非优势眼时的抓握熟练度。第二个实验通过在一只眼睛上放置散焦的低度数或高度数镜片，来暂时模拟正常成年人中类似的立体视敏度损失，并将其与对照（中性镜片）双眼视觉表现进行比较。在每种观察条件下，对受试者优势手在伸手、精确抓握和提起圆柱形物体（两种尺寸，四个位置）时进行40至48次试验，记录其运动，对抓握计划和执行的运动学及误差测量进行量化。
与双眼视觉降低相比，正常双眼视觉时的表现更快、更准确，而单眼条件下的表现最差。每当正常立体视觉永久性降低（方差分析P<0.05）或短暂降低（方差分析P<0.001）时，运动持续时间都会延长（最长约100毫秒），抓握执行时的错误率会翻倍（方差分析P<0.001）。伸手时的双眼缺陷出现在其末期阶段（最终接近时间延长、速度校正更多、与物体接触时的协调性更差），并且通常随着现有的视差敏感度损失而增加。双眼抓握受到立体视敏度损失的影响更均匀，并且受其持续时间的影响。长期存在立体视觉缺陷的成年人在最初接触物体时手指放置的变异性增加，并且他们通过延长（约25%）随后施加抓握的时间来进行适应（方差分析P<0.001）。短暂的立体视觉降低导致初始手指放置出现系统性偏移，抓握位置的接触后调整增加两到三倍（方差分析P<0.01）。
高质量的双眼立体视觉对于熟练的精确抓握至关重要。视差敏感度降低会导致抓握点选择不准确，并且更依赖来自物体接触的非视觉（本体感觉）信息来控制抓握稳定性。
