Department of Neuroscience, Erasmus University Medical Centre Rotterdam, Dr. Molewaterplein 50, 3000 DR Rotterdam, The Netherlands.
Neuroscience. 2013 Aug 29;246:73-81. doi: 10.1016/j.neuroscience.2013.04.029. Epub 2013 Apr 30.
Vestibulo-ocular reflexes are the fastest compensatory reflex systems. One of these is the translational vestibulo-ocular reflex (TVOR) which stabilizes the gaze at a given fixation point during whole body translations. For a proper response of the TVOR the eyes have to counter rotate in the head with a velocity that is inversely scaled to viewing distance of the target. It is generally assumed that scaling of the TVOR is automatically coupled to vergence angle at the brainstem level. However, different lines of evidence also argue that in humans scaling of the TVOR also depends on a mechanism that pre-sets gain on a priori knowledge of target distance. To discriminate between these two possibilities we used a real target paradigm with vergence angle coupled to distance and a virtual target paradigm with vergence angle dissociated from target distance. We compared TVOR responses in six subjects who underwent lateral sinusoidal whole-body translations at 1 and 2 Hz. Real targets varied between distance of 50 and 22.4 cm in front of the subjects, whereas the virtual targets consisting of a green and red light emitting diode (LED) were physically located at 50 cm from the subject. Red and green LED's were dichoptically viewed. By shifting the red LED relative to the green LED we created a range of virtual viewing distances where vergence angle changed but the ideal kinematic eye velocity was always the same. Eye velocity data recorded with virtual targets were compared to eye velocity data recorded with real targets. We also used flashing targets (flash frequency 1 Hz, duration 5 ms). During the real, continuous visible targets condition scaling of compensatory eye velocity with vergence angle was nearly perfect. During viewing of virtual targets, and with flashed targets compensatory eye velocity only weakly correlated to vergence angle, indicating that vergence angle is only partially coupled to compensatory eye velocity during translation. Our data suggest that in humans vergence angle as a measure of target distance estimation has only limited use for automatic TVOR scaling.
前庭眼反射是最快的补偿反射系统之一。其中之一是平移性前庭眼反射（TVOR），它在整个身体平移过程中稳定注视在给定的注视点。为了使 TVOR 得到适当的反应，眼睛必须在头部中反向旋转，其速度与目标的观察距离成反比。一般认为，TVOR 的缩放自动耦合到脑干水平的聚散角。然而，不同的证据也表明，在人类中，TVOR 的缩放还取决于一种机制，该机制根据目标距离的先验知识预先设置增益。为了区分这两种可能性，我们使用了一个真实目标范式，其中聚散角与距离耦合，以及一个虚拟目标范式，其中聚散角与目标距离分离。我们比较了六位受试者在 1 和 2 Hz 的横向正弦全身平移时的 TVOR 反应。真实目标在距离受试者 50 到 22.4 厘米之间变化，而虚拟目标由一个绿色和红色发光二极管（LED）组成，物理上位于距离受试者 50 厘米处。红色和绿色 LED 是双视的。通过将红色 LED 相对于绿色 LED 移动，我们创建了一个虚拟观看距离范围，其中聚散角发生变化，但理想的运动眼球速度始终相同。用虚拟目标记录的眼球速度数据与用真实目标记录的眼球速度数据进行了比较。我们还使用了闪烁的目标（闪烁频率 1 Hz，持续时间 5 ms）。在真实的、连续可见目标条件下，补偿眼球速度与聚散角的缩放几乎是完美的。在观看虚拟目标和闪烁目标时，补偿眼球速度仅与聚散角弱相关，这表明在平移过程中，聚散角仅部分耦合到补偿眼球速度。我们的数据表明，在人类中，作为目标距离估计的聚散角对于自动 TVOR 缩放的使用有限。
