Chang Acer Y-C, Schwartzman David J, VanRullen Rufin, Kanai Ryota, Seth Anil K
Department of Informatics, University of Sussex, Brighton BN1 9QJ, United Kingdom,
Sackler Centre for Consciousness Science, University of Sussex, Brighton BN1 9QJ, United Kingdom.
J Neurosci. 2017 Aug 30;37(35):8486-8497. doi: 10.1523/JNEUROSCI.3714-16.2017. Epub 2017 Aug 1.
A novel neural signature of active visual processing has recently been described in the form of the "perceptual echo", in which the cross-correlation between a sequence of randomly fluctuating luminance values and occipital electrophysiological signals exhibits a long-lasting periodic (∼100 ms cycle) reverberation of the input stimulus (VanRullen and Macdonald, 2012). As yet, however, the mechanisms underlying the perceptual echo and its function remain unknown. Reasoning that natural visual signals often contain temporally predictable, though nonperiodic features, we hypothesized that the perceptual echo may reflect a periodic process associated with regularity learning. To test this hypothesis, we presented subjects with successive repetitions of a rapid nonperiodic luminance sequence, and examined the effects on the perceptual echo, finding that echo amplitude linearly increased with the number of presentations of a given luminance sequence. These data suggest that the perceptual echo reflects a neural signature of regularity learning.Furthermore, when a set of repeated sequences was followed by a sequence with inverted luminance polarities, the echo amplitude decreased to the same level evoked by a novel stimulus sequence. Crucially, when the original stimulus sequence was re-presented, the echo amplitude returned to a level consistent with the number of presentations of this sequence, indicating that the visual system retained sequence-specific information, for many seconds, even in the presence of intervening visual input. Altogether, our results reveal a previously undiscovered regularity learning mechanism within the human visual system, reflected by the perceptual echo. How the brain encodes and learns fast-changing but nonperiodic visual input remains unknown, even though such visual input characterizes natural scenes. We investigated whether the phenomenon of "perceptual echo" might index such learning. The perceptual echo is a long-lasting reverberation between a rapidly changing visual input and evoked neural activity, apparent in cross-correlations between occipital EEG and stimulus sequences, peaking in the alpha (∼10 Hz) range. We indeed found that perceptual echo is enhanced by repeatedly presenting the same visual sequence, indicating that the human visual system can rapidly and automatically learn regularities embedded within fast-changing dynamic sequences. These results point to a previously undiscovered regularity learning mechanism, operating at a rate defined by the alpha frequency.
最近，一种新的主动视觉处理神经特征以“感知回声”的形式被描述出来，即随机波动的亮度值序列与枕叶电生理信号之间的互相关显示出输入刺激的持久周期性（约100毫秒周期）回响（范鲁伦和麦克唐纳，2012年）。然而，到目前为止，感知回声背后的机制及其功能仍然未知。鉴于自然视觉信号通常包含时间上可预测但非周期性的特征，我们推测感知回声可能反映了与规律性学习相关的周期性过程。为了验证这一假设，我们向受试者呈现快速非周期性亮度序列的连续重复，并检查对感知回声的影响，发现回声幅度随给定亮度序列的呈现次数线性增加。这些数据表明感知回声反映了规律性学习的神经特征。此外，当一组重复序列之后是具有相反亮度极性的序列时，回声幅度降至由新刺激序列诱发的相同水平。至关重要的是，当原始刺激序列再次呈现时，回声幅度恢复到与该序列呈现次数一致的水平，表明视觉系统即使在存在中间视觉输入的情况下，也能在数秒内保留序列特异性信息。总之，我们的结果揭示了人类视觉系统中一种以前未被发现的规律性学习机制，由感知回声反映出来。大脑如何编码和学习快速变化但非周期性的视觉输入仍然未知，尽管这种视觉输入是自然场景的特征。我们研究了“感知回声”现象是否可能指示这种学习。感知回声是快速变化的视觉输入与诱发的神经活动之间的持久回响，在枕叶脑电图与刺激序列之间的互相关中明显可见，在阿尔法（约10赫兹）范围内达到峰值。我们确实发现，通过反复呈现相同的视觉序列可以增强感知回声，这表明人类视觉系统可以快速自动地学习嵌入在快速变化的动态序列中的规律。这些结果指向一种以前未被发现的规律性学习机制，以阿尔法频率定义的速率运行。
