Vercher J L, Gauthier G M
Département de Psychophysiologie, Université de Provence, Marseille, France.
J Vestib Res. 1990;1(2):161-70.
To maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counter-rotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the optokinetic reflex. A problem of importance relates to the value of the so-called intrinsic gain of the VOR (VORG) in man, and how this gain is modulated to provide appropriate eye movements. We have studied these problems in two situations: 1. fixation of a stationary object of the visual space while the head moves; 2. fixation of an object moving with the head. These two situations were compared to a basic condition in which no visual target was allowed in order to induce "pure" VOR. Eye movements were recorded in seated subjects during stationary sinusoidal and transient rotations around the vertical axis. Subjects were in total darkness (DARK condition) and involved in mental arithmetic. Alternatively, they were provided with a small foveal target, either fixed with respect to earth (earth-fixed target: EFT condition), or moving with them (chair-fixed-target: CFT condition). The stationary rotation experiment was used as baseline for the ensuing experiment and yielded control data in agreement with the literature. In all 3 visual conditions, typical responses to transient rotations were rigorously identical during the first 200 ms. They showed, sequentially, a 16-ms delay of the eye behind the head and a rapid increase in eye velocity during 75 to 80 ms, after which the average VORG was 0.9 +/- 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 200 ms, the VORG remained around 0.9 in DARK and increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of the later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit, and position error through saccades. Our data also show that in total darkness VORG is set to 0.9 in man. Lower values reported in the literature essentially reflect predictive properties of the vestibulo-ocular mechanism, particularly evident when the input signal is a sinewave.
为保持清晰的视觉，视网膜上的图像必须保持相当稳定。头部运动通常通过前庭眼反射（VOR）和视动反射的联合作用引起的眼球反向旋转而成功应对。一个重要问题涉及人类中所谓的VOR内在增益（VORG）的值，以及该增益如何被调节以提供适当的眼球运动。我们在两种情况下研究了这些问题：1. 头部移动时注视视觉空间中的静止物体；2. 注视随头部移动的物体。将这两种情况与不允许有视觉目标以诱导“纯”VOR的基本条件进行比较。在坐位受试者围绕垂直轴进行静止正弦和瞬态旋转期间记录眼球运动。受试者处于完全黑暗（黑暗条件）并进行心算。或者，为他们提供一个小的中央凹目标，该目标相对于地球固定（地球固定目标：EFT条件）或与他们一起移动（椅子固定目标：CFT条件）。静止旋转实验用作后续实验的基线，并产生与文献一致的对照数据。在所有3种视觉条件下，对瞬态旋转的典型反应在最初200毫秒内严格相同。它们依次显示眼球滞后头部16毫秒，以及在75至80毫秒期间眼球速度快速增加，此后平均VORG为0.9±0.15。在接下来的50至100毫秒内，所有三种条件下增益都保持在约0.9左右。超过200毫秒后，黑暗条件下VORG保持在约0.9左右，而在EFT和CFT条件下分别缓慢增加至1或降至零。后期事件的时间进程表明视觉跟踪机制开始起作用，通过平滑追踪减少视网膜滑动，并通过扫视减少位置误差。我们的数据还表明，在完全黑暗中，人类的VORG设定为0.9。文献中报道的较低值基本上反映了前庭眼机制的预测特性，当输入信号为正弦波时尤为明显。
