Edelman Jay A, Xu Kitty Z
Department of Biology, The City College of New York, New York, New York 10034, USA.
J Neurophysiol. 2009 Mar;101(3):1222-34. doi: 10.1152/jn.90708.2008. Epub 2008 Nov 19.
Saccadic eye movements are made both to explore the visual world and to react to sudden sensory events. We studied the ability for humans to execute a voluntary (i.e., nonstimulus-driven) saccade command in the face of a suddenly appearing visual stimulus. Subjects were required to make a saccade to a memorized location when a central fixation point disappeared. At varying times relative to fixation point disappearance a visual distractor appeared at a random location. When the distractor appeared at locations distant from the target virtually no saccades were initiated in a 30- to 40-ms interval beginning 70-80 ms after appearance of the distractor. If the distractor was presented slightly earlier relative to saccade initiation then saccades tended to have smaller amplitudes, with velocity profiles suggesting that the distractor terminated them prematurely. In contrast, distractors appearing close to the saccade target elicited express saccade-like movements 70-100 ms after their appearance, although the saccade endpoint was generally scarcely affected by the distractor. An additional experiment showed that these effects were weaker when the saccade was made to a visible target in a delayed task and still weaker when the saccade itself was made in response to the abrupt appearance of a visual stimulus. A final experiment revealed that the effect is smaller, but quite evident, for very small stimuli. These results suggest that the transient component of a visual response can briefly but almost completely suppress a voluntary saccade command, but only when the stimulus evoking that response is distant from the saccade goal.
扫视眼动既用于探索视觉世界，也用于对突发的感官事件做出反应。我们研究了人类在面对突然出现的视觉刺激时执行自愿性（即非刺激驱动）扫视指令的能力。当中央注视点消失时，受试者被要求向记忆中的位置进行扫视。在相对于注视点消失的不同时间，一个视觉干扰物出现在随机位置。当干扰物出现在远离目标的位置时，在干扰物出现后70 - 80毫秒开始的30 - 40毫秒间隔内，几乎没有引发扫视。如果干扰物相对于扫视启动稍微提前呈现，那么扫视的幅度往往较小，速度曲线表明干扰物过早地终止了它们。相比之下，出现在靠近扫视目标处的干扰物在出现后70 - 100毫秒会引发类似快速扫视的运动，尽管扫视终点通常几乎不受干扰物影响。另一个实验表明，当在延迟任务中向可见目标进行扫视时，这些效应较弱，而当扫视本身是对视觉刺激的突然出现做出反应时，效应更弱。最后一个实验表明，对于非常小的刺激，这种效应较小但相当明显。这些结果表明，视觉反应的瞬态成分可以短暂但几乎完全抑制自愿性扫视指令，但前提是引发该反应的刺激远离扫视目标。
