Humans are able to generate target-directed visuomotor responses in less than 100ms after stimulus onset. These "express" responses have been termed stimulus-locked responses (SLRs) and are proposed to be modulated by visuomotor transformations performed subcortically via the superior colliculus. Unfortunately, these responses have proven difficult to detect consistently across individuals. The recent report of an effective paradigm for generating SLRs in 100% of participants appears to change this. The task required the interception of a target moving at a constant velocity that emerged from behind a barrier. Here we aimed to reproduce the efficacy of this paradigm for eliciting SLRs and to test the hypothesis that its effectiveness derives from the predictability of target onset time as opposed to target motion per se. In one experiment, we recorded surface EMG from shoulder muscles as participants made reaches to intercept temporally predictable or unpredictable targets. Consistent with our hypothesis, predictably timed targets produced more frequent and stronger SLRs than unpredictably timed targets. In a second experiment, we compared different temporally predictable stimuli and observed that transiently presented targets produced larger and earlier SLRs than sustained moving targets. Our results suggest that target motion is not critical for facilitating the SLR expression and that timing predictability does not rely on extrapolation of a physically plausible motion trajectory. These findings provide support for a mechanism whereby an internal timer, probably located in cerebral cortex, primes the processing of both visual input and motor output within the superior colliculus to produce SLRs.

中文翻译：

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时间可预测性对表达视觉​​运动反应的影响

人类能够在刺激开始后不到 100 毫秒内产生目标导向的视觉运动反应。这些“表达”反应被称为刺激锁定反应 (SLRs)，并建议通过上丘皮质下执行的视觉运动转换来调节。不幸的是，这些反应已被证明难以在个体之间一致地检测到。最近关于在 100% 的参与者中生成 SLR 的有效范例的报告似乎改变了这一点。该任务需要拦截从障碍物后面出现的以恒定速度移动的目标。在这里，我们旨在重现这种范式在引发 SLR 方面的功效，并测试其有效性源自目标起始时间的可预测性而不是目标运动本身的假设。在一项实验中，当参与者伸手拦截时间上可预测或不可预测的目标时，我们记录了肩部肌肉的表面 EMG。与我们的假设一致，可预测的定时目标比不可预测的定时目标产生更频繁和更强的 SLR。在第二个实验中，我们比较了不同的时间可预测刺激，并观察到瞬时呈现的目标比持续移动的目标产生更大和更早的 SLR。我们的结果表明，目标运动对于促进 SLR 表达并不重要，并且时间可预测性不依赖于物理上合理的运动轨迹的外推。这些发现为一种机制提供了支持，该机制可能位于大脑皮层的内部计时器，