Bronstein A M, Gresty M A
Institute of Neurology, National Hospital, Queen Square, London, UK.
Exp Brain Res. 1991;85(3):697-700. doi: 10.1007/BF00231756.
Orbital motion of the head with the face directed towards the axis of rotation is a stimulus to the otolith organs which is in the opposite rightwards-left-wards sense to the rotational stimulus to the semicircular canals. This can be experienced, for example, by a child held at arms length "en face' and swung from side to side. As one swings, say to the right, the child's head rotates to its right yet moves linearly to its left. Eye movement responses to a transient orbital movement were observed whilst subjects fixated earth-fixed targets. i) a "near target" placed between the head and the axis whose relative displacement is in the same direction as head rotation, and ii) a "far target" placed beyond the axis whose relative motion is in the opposite direction to head rotation. The motion stimuli evoked slow phase eye movements at 45 ms latency, always in the opposite direction to head rotation, thus compensating for the motion of the far target but in the wrong direction for fixating the near target. Theoretically, fixating the near target demands a predominance of the otolith ocular-reflex, which would give an eye movement in the correct direction. However, despite visual cues, it seems that if the canal and otolith-ocular reflexes are evoked in opposing directions, the otolith reflex fails to operate at a sensitivity sufficiently high to reverse the direction of the canal-reflex.
头部朝着旋转轴方向运动且面部朝向旋转轴时，对耳石器官而言是一种刺激，这种刺激与对半规管的旋转刺激在左右方向上相反。例如，一个被伸直手臂“面对面”抱着的孩子左右摇晃时就能体验到这种情况。当摇晃时，比如说向右，孩子的头部向右旋转，但却向左做直线运动。在受试者注视固定于地面的目标时，观察到了对短暂轨道运动的眼球运动反应。i）一个“近目标”置于头部与旋转轴之间，其相对位移与头部旋转方向相同；ii）一个“远目标”置于旋转轴之外，其相对运动与头部旋转方向相反。运动刺激在45毫秒潜伏期诱发了慢相眼球运动，其方向始终与头部旋转方向相反，从而补偿了远目标的运动，但对于注视近目标而言方向错误。从理论上讲，注视近目标需要耳石眼反射占主导，这会使眼球运动方向正确。然而，尽管有视觉线索，但似乎如果半规管和耳石眼反射以相反方向诱发，耳石反射无法以足够高的敏感度起作用来反转半规管反射的方向。
