Barnes G R
Faculty of Life Sciences, University of Manchester, Moffat Building, Sackville St., Manchester M60 1QD, United Kingdom.
Brain Cogn. 2008 Dec;68(3):309-26. doi: 10.1016/j.bandc.2008.08.020. Epub 2008 Oct 10.
Ocular pursuit movements allow moving objects to be tracked with a combination of smooth movements and saccades. The principal objective is to maintain smooth eye velocity close to object velocity, thus minimising retinal image motion and maintaining acuity. Saccadic movements serve to realign the image if it falls outside the fovea, the area of highest acuity. Pursuit movements are often portrayed as voluntary but their basis lies in processes that sense retinal motion and can induce eye movements without active participation. The factor distinguishing pursuit from such reflexive movements is the ability to select and track a single object when presented with multiple stimuli. The selective process requires attention, which appears to raise the gain for the selected object and/or suppress that associated with other stimuli, the resulting competition often reducing pursuit velocity. Although pursuit is essentially a feedback process, delays in motion processing create problems of stability and speed of response. This is countered by predictive processes, probably operating through internal efference copy (extra-retinal) mechanisms using short-term memory to store velocity and timing information from prior stimulation. In response to constant velocity motion, the initial response is visually driven, but extra-retinal mechanisms rapidly take over and sustain pursuit. The same extra-retinal mechanisms may also be responsible for generating anticipatory smooth pursuit movements when past experience creates expectancy of impending object motion. Similar, but more complex, processes appear to operate during periodic pursuit, where partial trajectory information is stored and released in anticipation of expected future motion, thus minimising phase errors associated with motion processing delays.
眼球追踪运动可通过平滑运动和扫视的组合来追踪移动的物体。主要目的是使眼球的平滑速度接近物体速度，从而将视网膜图像运动降至最低并保持敏锐度。如果图像落在中央凹（敏锐度最高的区域）之外，扫视运动则用于重新对齐图像。追踪运动通常被描述为自愿性的，但其基础在于感知视网膜运动的过程，这些过程可以在没有主动参与的情况下诱发眼球运动。将追踪与这种反射性运动区分开来的因素是在面对多个刺激时选择并追踪单个物体的能力。选择性过程需要注意力，这似乎会提高所选物体的增益和/或抑制与其他刺激相关的增益，由此产生的竞争通常会降低追踪速度。尽管追踪本质上是一个反馈过程，但运动处理中的延迟会产生稳定性和反应速度方面的问题。这可以通过预测过程来抵消，预测过程可能通过内部传出副本（视网膜外）机制起作用，利用短期记忆存储来自先前刺激的速度和时间信息。对于匀速运动，最初的反应是由视觉驱动的，但视网膜外机制会迅速接管并维持追踪。当过去的经验产生对即将到来的物体运动的预期时，同样的视网膜外机制也可能负责产生预期的平滑追踪运动。在周期性追踪过程中，似乎也有类似但更复杂的过程在起作用，在这种情况下，部分轨迹信息会被存储并在预期未来运动时释放，从而将与运动处理延迟相关的相位误差降至最低。
