Lappe M, Pekel M, Hoffmann K P
Department of Zoology and Neurobiology, Ruhr University Bochum, D-44780 Bochum, Germany.
J Neurophysiol. 1998 Mar;79(3):1461-80. doi: 10.1152/jn.1998.79.3.1461.
We recorded spontaneous eye movements elicited by radial optic flow in three macaque monkeys using the scleral search coil technique. Computer-generated stimuli simulated forward or backward motion of the monkey with respect to a number of small illuminated dots arranged on a virtual ground plane. We wanted to see whether optokinetic eye movements are induced by radial optic flow stimuli that simulate self-movement, quantify their parameters, and consider their effects on the processing of optic flow. A regular pattern of interchanging fast and slow eye movements with a frequency of 2 Hz was observed. When we shifted the horizontal position of the focus of expansion (FOE) during simulated forward motion (expansional optic flow), median horizontal eye position also shifted in the same direction but only by a smaller amount; for simulated backward motion (contractional optic flow), median eye position shifted in the opposite direction. We relate this to a change in Schlagfeld typically observed in optokinetic nystagmus. Direction and speed of slow phase eye movements were compared with the local flow field motion in gaze direction (the foveal flow). Eye movement direction matched well the foveal motion. Small systematic deviations could be attributed to an integration of the global motion pattern. Eye speed on average did not match foveal stimulus speed, as the median gain was only approximately 0.5-0.6. The gain was always lower for expanding than for contracting stimuli. We analyzed the time course of the eye movement immediately after each saccade. We found remarkable differences in the initial development of gain and directional following for expansion and contraction. For expansion, directional following and gain were initially poor and strongly influenced by the ongoing eye movement before the saccade. This was not the case for contraction. These differences also can be linked to properties of the optokinetic system. We conclude that optokinetic eye movements can be elicited by radial optic flow fields simulating self-motion. These eye movements are linked to the parafoveal flow field, i.e., the motion in the direction of gaze. In the retinal projection of the optic flow, such eye movements superimpose retinal slip. This results in complex retinal motion patterns, especially because the gain of the eye movement is small and variable. This observation has special relevance for mechanisms that determine self-motion from retinal flow fields. It is necessary to consider the influence of eye movements in optic flow analysis, but our results suggest that direction and speed of an eye movement should be treated differently.
我们使用巩膜搜索线圈技术记录了三只猕猴在径向光流刺激下引发的自发性眼动。计算机生成的刺激模拟了猴子相对于排列在虚拟地面平面上的多个小亮点的向前或向后运动。我们想了解模拟自我运动的径向光流刺激是否会诱发视动性眼动，量化其参数，并考虑它们对视流处理的影响。观察到一种频率为2Hz的快速和慢速眼动交替的规律模式。当我们在模拟向前运动（扩张性光流）期间改变扩张中心（FOE）的水平位置时，水平眼位中位数也会向相同方向移动，但移动量较小；对于模拟向后运动（收缩性光流），眼位中位数向相反方向移动。我们将此与视动性眼球震颤中通常观察到的Schlagfeld变化联系起来。将慢相眼动的方向和速度与注视方向（中央凹光流）上的局部流场运动进行比较。眼动方向与中央凹运动匹配良好。小的系统性偏差可归因于全局运动模式的整合。平均眼速与中央凹刺激速度不匹配，因为中位数增益仅约为0.5 - 0.6。扩张刺激的增益总是低于收缩刺激。我们分析了每次扫视后眼动的时间进程。我们发现扩张和收缩在增益和方向跟随的初始发展方面存在显著差异。对于扩张，方向跟随和增益最初较差，并且在扫视前受到正在进行的眼动的强烈影响。收缩情况并非如此。这些差异也可以与视动系统的特性联系起来。我们得出结论，模拟自我运动的径向光流场可以诱发视动性眼动。这些眼动与中央凹旁流场相关，即注视方向上的运动。在光流的视网膜投影中，这种眼动会叠加视网膜滑移。这导致了复杂的视网膜运动模式，特别是因为眼动的增益较小且可变。这一观察结果对于从视网膜流场确定自我运动的机制具有特殊意义。在光流分析中考虑眼动的影响是必要的，但我们的结果表明，眼动的方向和速度应区别对待。
