Department of Cognitive Neuroscience, Universität Bielefeld, Bielefeld, Germany ; Cognitive Interaction Technology Center of Excellence, Universität Bielefeld, Bielefeld, Germany.
PLoS One. 2013 Oct 30;8(10):e78757. doi: 10.1371/journal.pone.0078757. eCollection 2013.
Random errors are omnipresent in sensorimotor tasks due to perceptual and motor noise. The question is, are humans aware of their random errors on an instance-by-instance basis? The appealing answer would be 'no' because it seems intuitive that humans would otherwise immediately correct for the errors online, thereby increasing sensorimotor precision. However, here we show the opposite. Participants pointed to visual targets with varying degree of feedback. After movement completion participants indicated whether they believed they landed left or right of target. Surprisingly, participants' left/right-discriminability was well above chance, even without visual feedback. Only when forced to correct for the error after movement completion did participants loose knowledge about the remaining error, indicating that random errors can only be accessed offline. When correcting, participants applied the optimal correction gain, a weighting factor between perceptual and motor noise, minimizing end-point variance. Together these results show that humans optimally combine direct information about sensorimotor noise in the system (the current random error), with indirect knowledge about the variance of the perceptual and motor noise distributions. Yet, they only appear to do so offline after movement completion, not while the movement is still in progress, suggesting that during movement proprioceptive information is less precise.
由于感知和运动噪声的存在，感觉运动任务中存在着无处不在的随机误差。问题是，人类是否能逐个实例地意识到自己的随机误差？一个吸引人的答案是“否”，因为直观地说，人类否则会立即在线纠正错误，从而提高感觉运动精度。然而，在这里我们展示的是相反的情况。参与者用不同程度的反馈指向视觉目标。运动完成后，参与者指出他们是否认为自己的落点在目标的左侧或右侧。令人惊讶的是，参与者的左右分辨能力明显高于随机水平，即使没有视觉反馈也是如此。只有在运动完成后被迫纠正错误时，参与者才会失去对剩余错误的了解，这表明随机错误只能离线访问。在进行纠正时，参与者应用了最佳的纠正增益，即感知和运动噪声之间的权重因子，以最小化端点方差。这些结果表明，人类最优地结合了系统中关于感觉运动噪声的直接信息（当前的随机误差），以及关于感知和运动噪声分布方差的间接知识。然而，它们似乎只在运动完成后离线进行，而不是在运动进行时进行，这表明在运动过程中本体感觉信息不太准确。
