Center for Systems Engineering and Applied Mechanics, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
J Neurophysiol. 2010 Jan;103(1):543-56. doi: 10.1152/jn.00656.2009. Epub 2009 Nov 18.
Spatial updating is the ability to keep track of the position of world-fixed objects while we move. In the case of vision, this phenomenon is called spatial constancy and has been studied in head-restraint conditions. During head-restrained smooth pursuit, it has been shown that the saccadic system has access to extraretinal information from the pursuit system to update the objects' position in the surrounding environment. However, during head-unrestrained smooth pursuit, the saccadic system needs to keep track of three different motor commands: the ocular smooth pursuit command, the vestibuloocular reflex (VOR), and the head movement command. The question then arises whether saccades compensate for these movements. To address this question, we briefly presented a target during sinusoidal head-unrestrained smooth pursuit in darkness. Subjects were instructed to look at the flash as soon as they saw it. We observed that subjects were able to orient their gaze to the memorized (and spatially updated) position of the flashed target generally using one to three successive saccades. Similar to the behavior in the head-restrained condition, we found that the longer the gaze saccade latency, the better the compensation for intervening smooth gaze displacements; after about 400 ms, 62% of the smooth gaze displacement had been compensated for. This compensation depended on two independent parameters: the latency of the saccade and the eye contribution to the gaze displacement during this latency period. Separating gaze into eye and head contributions, we show that the larger the eye contribution to the gaze displacement, the better the overall compensation. Finally, we found that the compensation was a function of the head oscillation frequency and we suggest that this relationship is linked to the modulation of VOR gain. We conclude that the general mechanisms of compensation for smooth gaze displacements are similar to those observed in the head-restrained condition.
空间更新是指在我们移动时跟踪世界固定物体位置的能力。在视觉的情况下，这种现象被称为空间恒常性，并在头固定条件下进行了研究。在头固定平滑追踪期间，已经表明扫视系统可以从追踪系统获取视网膜外信息，以更新周围环境中物体的位置。然而，在头不固定平滑追踪期间，扫视系统需要跟踪三个不同的运动指令：眼球平滑追踪指令、前庭眼反射（VOR）和头部运动指令。那么问题就来了，扫视是否会补偿这些运动。为了解决这个问题，我们在黑暗中在正弦曲线头不固定平滑追踪期间短暂呈现一个目标。要求受试者一旦看到闪光就注视它。我们观察到，受试者通常使用一个到三个连续的扫视来将目光定位到记忆中的（并空间更新的）闪光目标位置。与头固定条件下的行为类似，我们发现注视扫视潜伏期越长，对平滑注视位移的补偿越好；在大约 400 毫秒后，62%的平滑注视位移得到了补偿。这种补偿取决于两个独立的参数：扫视的潜伏期和在潜伏期内眼睛对视点位移的贡献。将注视分为眼睛和头部贡献，我们表明眼睛对视点位移的贡献越大，整体补偿效果越好。最后，我们发现补偿是头部摆动频率的函数，我们建议这种关系与 VOR 增益的调制有关。我们得出结论，平滑注视位移补偿的一般机制与在头固定条件下观察到的机制相似。
