Wallman J, Fuchs A F
Department of Biology, City College, City University of New York, New York 10031, USA.
J Neurophysiol. 1998 Nov;80(5):2405-16. doi: 10.1152/jn.1998.80.5.2405.
The brain maintains the accuracy of saccadic eye movements by adjusting saccadic amplitude relative to the target distance (i.e., saccade gain) on the basis of the performance of recent saccades. If an experimenter surreptitiously moves the target backward during each saccade, thereby causing the eyes to land beyond their targets, saccades undergo a gradual gain reduction. The error signal driving this conventional saccadic gain adaptation could be either visual (the postsaccadic distance of the target from the fovea) or motoric (the direction and size of the corrective saccade that brings the eye onto the back-stepped target). Similarly, the adaptation itself might be a motor adjustment (change in the size of saccade for a given perceived target distance) or a visual remapping (change in the perceived target distance). We studied these possibilities in experiments both with rhesus macaques and with humans. To test whether the error signal is motoric, we used a paradigm devised by Heiner Deubel. The Deubel paradigm differed from the conventional adaptation paradigm in that the backward step that occurred during the saccade was brief, and the target then returned to its original displaced location. This ploy replaced most of the usual backward corrective saccades with forward ones. Nevertheless, saccadic gain gradually decreased over hundreds of trials. Therefore, we conclude that the direction of saccadic gain adaptation is not determined by the direction of corrective saccades. To test whether gain adaptation is a manifestation of a static visual remapping, we decreased the gain of 10 degrees horizontal saccades by conventional adaptation and then tested the gain to targets appearing at retinal locations unused during adaptation. To make the target appear in such "virgin territory," we had it jump first vertically and then 10 degrees horizontally; both jumps were completed and the target spot extinguished before saccades were made sequentially to the remembered target locations. Conventional adaptation decreased the gain of the second, horizontal saccade even though the target was in a nonadapted retinal location. In contrast, the horizontal component of oblique saccades made directly to the same virgin location showed much less gain decrease, suggesting that the adaptation is specific to saccade direction rather than to target location. Thus visual remapping cannot account for the entire reduction of saccadic gain. We conclude that saccadic gain adaptation involves an error signal that is primarily visual, not motor, but that the adaptation itself is primarily motor, not visual.
大脑通过根据近期扫视的表现来调整扫视幅度与目标距离的关系（即扫视增益），从而维持扫视眼动的准确性。如果实验者在每次扫视过程中偷偷将目标向后移动，导致眼睛落在目标之外，扫视的增益会逐渐降低。驱动这种传统扫视增益适应的误差信号可能是视觉的（目标相对于中央凹的扫视后距离）或运动的（将眼睛带到后移目标上的校正扫视的方向和大小）。同样，适应本身可能是一种运动调整（对于给定的感知目标距离，扫视大小的变化）或视觉重映射（感知目标距离的变化）。我们在恒河猴和人类的实验中研究了这些可能性。为了测试误差信号是否是运动性的，我们使用了海纳·德贝尔设计的范式。德贝尔范式与传统适应范式的不同之处在于，扫视过程中发生的向后移动是短暂的，然后目标会回到其原来的移位位置。这种策略用向前的扫视取代了大部分通常的向后校正扫视。然而，在数百次试验中，扫视增益逐渐降低。因此，我们得出结论，扫视增益适应的方向不是由校正扫视的方向决定的。为了测试增益适应是否是静态视觉重映射的表现，我们通过传统适应降低了10度水平扫视的增益，然后测试对在适应过程中未使用的视网膜位置出现的目标的增益。为了使目标出现在这样的“未使用区域”，我们让它先垂直跳跃，然后水平跳跃10度；两次跳跃都完成且目标点熄灭后，再依次向记忆中的目标位置进行扫视。传统适应降低了第二次水平扫视的增益，即使目标处于未适应的视网膜位置。相比之下，直接指向相同未使用位置的斜向扫视的水平分量显示增益降低要少得多，这表明适应特定于扫视方向而非目标位置。因此，视觉重映射不能解释扫视增益的全部降低。我们得出结论，扫视增益适应涉及一个主要是视觉而非运动的误差信号，但适应本身主要是运动的而非视觉的。
