Abstract:
The angular vestibulo-ocular reflex (aVOR) stabilizes retinal images by counter-rotating the eyes during head rotations. Perfect compensatory movements would thus rotate the eyes exactly opposite to the head, that is, eyes vs. head would exhibit a unity gain. However, in many species, but also in elderly humans or patients with a history of vestibular damage, the aVOR is far from compensatory with gains that are in part considerably lower than unity. The reason for this apparent suboptimality is unknown. Here, we propose that low VOR gain values reflect an optimal adaptation to sensory and motor signal variability. According to this hypothesis, gaze stabilization mechanisms that aim at minimizing the overall retinal image slip must consider the effects of (1) sensory and motor noise and (2) dynamic constraints of peripheral and central nervous processing. We demonstrate that a computational model for optimizing retinal image slip in the presence of such constraints of signal processing in fact predicts gain values smaller than unity. We further show specifically for tadpoles of the clawed toad, Xenopus laevis with particularly low gain values that previously reported VOR gains quantitatively correspond to the observed variability of eye movements and thus constitute an optimal adaptation mechanism. We thus hypothesize that lower VOR gain values in elderly human subjects or recovered patients with a history of vestibular damage may be the sign of an optimization given higher noise levels rather than a direct consequence of the damage, such as an inability of executing fast compensatory eye movements.
摘要:
角前庭-眼反射(aVOR)通过在头部旋转期间反向旋转眼睛来稳定视网膜图像。因此,完美的补偿运动将使眼睛与头部完全相反地旋转,也就是说,眼睛vs.头将表现出统一的增益。然而,在许多物种中,而且在老年人或有前庭损伤史的患者中,aVOR远非补偿性的,部分收益远低于统一。这种明显的次优性的原因是未知的。这里,我们认为低VOR增益值反映了对感觉和运动信号变异性的最佳适应。根据这个假设,旨在最大程度减少整体视网膜图像滑动的注视稳定机制必须考虑(1)感觉和运动噪声以及(2)周围和中枢神经处理的动态约束的影响。我们证明,在存在这种信号处理约束的情况下,用于优化视网膜图像滑动的计算模型实际上预测的增益值小于1。我们进一步展示了专门针对爪蟾蜍的t,先前报告的VOR增益具有特别低的增益值的非洲爪狼定量地对应于观察到的眼球运动的可变性,因此构成了最佳的适应机制。因此,我们假设老年受试者或有前庭损伤病史的康复患者的较低VOR增益值可能是优化的迹象,因为噪声水平较高,而不是损伤的直接后果。例如无法执行快速的补偿性眼动。