Weber H, Dürr N, Fischer B
Brain Research Unit, Institute of Biophysics, Freiburg, Germany.
Exp Brain Res. 1998 Jun;120(4):417-31. doi: 10.1007/s002210050415.
The reaction times of saccades (SRT) to a suddenly presented visual stimulus (pro-saccade) can be decreased and a separate mode of express saccades can occur when a gap paradigm is used (i.e. fixation-point offset precedes target onset by 200 ms). A valid peripheral cue, presented briefly (100 ms) before target onset, has been found to facilitate the generation of saccades to the target, thereby increasing the frequency of express saccades and decreasing the mean latency. This facilitation occurs only for cues that correctly indicate the direction of the subsequent target presentation (valid cues). The present study investigates the effects of valid cues on SRTs and error rate in the anti-saccade task (saccades in the direction opposite to the stimulus) by systematically varying the cue lead time (CLT) and using the gap and overlap conditions, i.e. fixation point remains on throughout the trial. For a CLT of 100 ms, both reaction times and error rates were significantly increased. With increasing CLT (200-500 ms), both the reaction times of the anti-saccades and the error rates returned to approximately control level, with CLT more than 200 ms in both the gap and the overlap condition. Additional experiments using non-informative cues in the overlap task showed that the reaction times of correct anti-saccades and the error rate were decreased when cue and stimulus appeared at the same side. Analysis of the erratic pro-saccades revealed that almost all of them were corrected, i.e. they were followed by a second saccade towards the required location. It is found that the correction times were usually very short, with intersaccadic intervals between 0 and 150 ms. We suggest that the orienting mechanism, elicited by a transient peripheral cue, relates to the command and the decision to make a pro- rather than an anti-saccade. The cue elicits pro-orienting towards its position when a pro-saccade is required, and anti-orienting when an anti-saccade is required. The orienting effect is transient and decays with CLTs of more than 200 ms; this result holds for both anti-saccades and pro-saccades. Since subjects reported that they could not prevent the erratic pro-saccades or were often not aware of them, we conclude that this orienting mechanism occurs automatically, beyond voluntary control.
当使用间隙范式（即注视点偏移先于目标呈现200毫秒）时，对突然呈现的视觉刺激做出的扫视反应时间（SRT）（顺向扫视）可以缩短，并且会出现一种单独的快速扫视模式。研究发现，在目标呈现前短暂呈现（100毫秒）的有效外周线索能够促进向目标的扫视生成，从而增加快速扫视的频率并缩短平均潜伏期。这种促进作用仅针对能正确指示后续目标呈现方向的线索（有效线索）。本研究通过系统改变线索提前时间（CLT）并使用间隙和重叠条件（即整个试验过程中注视点一直存在），研究了有效线索在反扫视任务（向与刺激相反方向的扫视）中对SRT和错误率的影响。对于100毫秒的CLT，反应时间和错误率均显著增加。随着CLT增加（200 - 500毫秒），反扫视的反应时间和错误率在间隙和重叠条件下均在CLT超过200毫秒时恢复到大致对照水平。在重叠任务中使用非信息性线索的额外实验表明，当线索和刺激出现在同一侧时，正确反扫视的反应时间和错误率会降低。对不稳定顺向扫视的分析表明，几乎所有这些扫视都得到了纠正，即随后会有第二次扫视指向所需位置。研究发现，纠正时间通常非常短，眼跳间隔在0到150毫秒之间。我们认为，由短暂外周线索引发的定向机制与做出顺向而非反扫视的指令和决策有关。当需要顺向扫视时，线索引发向其位置的顺向定向，而当需要反扫视时引发反向定向。定向效应是短暂的，并且在CLT超过200毫秒时会衰减；这一结果在反扫视和顺向扫视中均成立。由于受试者报告他们无法阻止不稳定的顺向扫视或常常未意识到它们，我们得出结论，这种定向机制是自动发生的，不受自主控制。
