Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
Invest Ophthalmol Vis Sci. 2013 Jun 27;54(6):4409-21. doi: 10.1167/iovs.12-11369.
Humans make smooth pursuit eye movements to bring the image of a moving object onto the fovea. Although pursuit accuracy is critical to prevent motion blur, the eye often falls behind the target. Previous studies suggest that pursuit accuracy differs between motion directions. Here, we systematically assess asymmetries in smooth pursuit.
In experiment 1, binocular eye movements were recorded while observers (n = 20) tracked a small spot of light moving along one of four cardinal or diagonal axes across a featureless background. We analyzed pursuit latency, acceleration, peak velocity, gain, and catch-up saccade latency, number, and amplitude. In experiment 2 (n = 22), we examined the effects of spatial location and constrained stimulus motion within the upper or lower visual field.
Pursuit was significantly faster (higher acceleration, peak velocity, and gain) and smoother (fewer and later catch-up saccades) in response to downward versus upward motion in both the upper and the lower visual fields. Pursuit was also more accurate and smoother in response to horizontal versus vertical motion. CONCLUSIONS. Our study is the first to report a consistent up-down asymmetry in human adults, regardless of visual field. Our findings suggest that pursuit asymmetries are adaptive responses to the requirements of the visual context: preferred motion directions (horizontal and downward) are more critical to our survival than nonpreferred ones.
人类进行平滑追踪眼动，以使运动物体的影像落在中央凹上。尽管追踪精度对于防止运动模糊至关重要，但眼睛常常会落后于目标。先前的研究表明，追踪精度在运动方向上存在差异。在这里，我们系统地评估了平滑追踪的不对称性。
在实验 1 中，当观察者（n=20）追踪一个小光点沿着四个方位或对角线之一在无特征的背景上运动时，记录双眼的眼动。我们分析了追踪潜伏期、加速度、峰值速度、增益和追上性眼跳潜伏期、数量和幅度。在实验 2（n=22）中，我们研究了空间位置和受限制刺激运动在上下视野内的影响。
无论是在上视野还是在下视野中，相对于向上运动，向下运动都能使追踪更快（更高的加速度、峰值速度和增益）、更平滑（更少和更迟的追上性眼跳）。相对于垂直运动，水平运动也能使追踪更准确和更平滑。
我们的研究首次报告了人类成年人中一致的上下不对称性，而与视野无关。我们的发现表明，追踪不对称性是对视觉环境要求的适应性反应：优先的运动方向（水平和向下）比非优先的运动方向对我们的生存更重要。
