Dept. of Neurology, Univ. Hospital Zurich, Zurich, Switzerland.
J Neurophysiol. 2012 Jun;107(11):3095-106. doi: 10.1152/jn.00724.2010. Epub 2012 Mar 21.
Gravicentric visual alignments become less precise when the head is roll-tilted relative to gravity, which is most likely due to decreasing otolith sensitivity. To align a luminous line with the perceived gravity vector (gravicentric task) or the perceived body-longitudinal axis (egocentric task), the roll orientation of the line on the retina and the torsional position of the eyes relative to the head must be integrated to obtain the line orientation relative to the head. Whether otolith input contributes to egocentric tasks and whether the modulation of variability is restricted to vision-dependent paradigms is unknown. In nine subjects we compared precision and accuracy of gravicentric and egocentric alignments in various roll positions (upright, 45°, and 75° right-ear down) using a luminous line (visual paradigm) in darkness. Trial-to-trial variability doubled for both egocentric and gravicentric alignments when roll-tilted. Two mechanisms might explain the roll-angle-dependent modulation in egocentric tasks: 1) Modulating variability in estimated ocular torsion, which reflects the roll-dependent precision of otolith signals, affects the precision of estimating the line orientation relative to the head; this hypothesis predicts that variability modulation is restricted to vision-dependent alignments. 2) Estimated body-longitudinal reflects the roll-dependent variability of perceived earth-vertical. Gravicentric cues are thereby integrated regardless of the task's reference frame. To test the two hypotheses the visual paradigm was repeated using a rod instead (haptic paradigm). As with the visual paradigm, precision significantly decreased with increasing head roll for both tasks. These findings propose that the CNS integrates input coded in a gravicentric frame to solve egocentric tasks. In analogy to gravicentric tasks, where trial-to-trial variability is mainly influenced by the properties of the otolith afferents, egocentric tasks may also integrate otolith input. Such a shared mechanism for both paradigms and frames of reference is supported by the significantly correlated trial-to-trial variabilities.
当头部相对于重力倾斜时，重心动视觉对齐会变得不那么精确，这很可能是由于耳石敏感性降低所致。为了使发光线与感知重力矢量（重心动任务）或感知身体纵轴（自心任务）对齐，必须整合视网膜上光线的滚动方向和眼睛相对于头部的扭转位置，以获得相对于头部的光线方向。耳石输入是否有助于自心任务，以及变异性的调制是否仅限于依赖视觉的范式，目前尚不清楚。在九名受试者中，我们在黑暗中使用发光线（视觉范式）比较了在各种倾斜位置（直立、45°和 75°右耳向下）下的重心动和自心对齐的精度和准确性。当倾斜时，自心和重心动对齐的试验间变异性都增加了一倍。有两种机制可能解释自心任务中与倾斜角度相关的调制：1）调制估计眼扭转的变异性，这反映了耳石信号的倾斜依赖性精度，影响了相对于头部估计线方向的精度；这个假设预测变异性调制仅限于依赖视觉的对齐。2）估计身体纵轴反映了感知地球垂直的倾斜依赖性变异性。重心动线索因此被整合，无论任务的参考框架如何。为了检验这两个假设，我们使用棒而不是线（触觉范式）重复了视觉范式。与视觉范式一样，对于两个任务，精度都随着头部倾斜的增加而显著降低。这些发现表明，中枢神经系统将以重心动框架编码的输入进行整合，以解决自心任务。与重心动任务类似，其中试验间变异性主要受耳石传入的特性影响，自心任务也可能整合耳石输入。这种用于两种范式和参考框架的共享机制得到了试验间变异性显著相关的支持。
