Center for Mind and Brain, University of California, Davis, California 95616, USA.
J Neurosci. 2010 Feb 3;30(5):1905-13. doi: 10.1523/JNEUROSCI.4391-09.2010.
In reverberant environments, the brain can suppress echoes so that auditory perception is dominated by the primary or leading sounds. Echo suppression comprises at least two distinct phenomena whose neural bases are unknown: spatial translocation of an echo toward the primary sound, and object capture to combine echo and primary sounds into a single event. In an electroencephalography study, we presented subjects with primary-echo (leading-lagging) click pairs in virtual acoustic space, with interclick delay at the individual's 50% suppression threshold. On each trial, subjects reported both click location (one or both hemifields) and the number of clicks they heard (one or two). Thus, the threshold stimulus led to two common percepts: Suppressed and Not Suppressed. On some trials, a subset of subjects reported an intermediate percept, in which two clicks were perceived in the same hemifield as the leading click, providing a dissociation between spatial translocation and object capture. We conducted time-frequency and event-related potential analyses to examine the time course of the neural mechanisms mediating echo suppression. Enhanced gamma band phase synchronization (peaking at approximately 40 Hz) specific to successful echo suppression was evident from 20 to 60 ms after stimulus onset. N1 latency provided a categorical neural marker of spatial translocation, whereas N1 amplitude still reflected the physical presence of a second (lagging) click. These results provide evidence that (1) echo suppression begins early, at the latest when the acoustic signal first reaches cortex, and (2) the brain spatially translocates a perceived echo before the primary sound captures it.
在混响环境中，大脑可以抑制回声，从而使听觉感知主要受原始或主导声音的支配。回声抑制至少包括两种不同的现象，其神经基础尚不清楚：回声向原始声音的空间移位，以及将回声和原始声音组合成单个事件的目标捕获。在一项脑电图研究中，我们在虚拟声空中向受试者呈现了原始-回声（领先-滞后）点击对，其点击间隔延迟为个体的 50%抑制阈值。在每次试验中，受试者报告点击的位置（一个或两个半视野）和听到的点击数量（一个或两个）。因此，阈值刺激导致了两种常见的感知：抑制和未抑制。在一些试验中，一部分受试者报告了一种中间感知，其中两个点击在与主导点击相同的半视野中被感知，从而在空间移位和目标捕获之间产生了分离。我们进行了时频和事件相关电位分析，以检查介导回声抑制的神经机制的时间进程。从刺激开始后 20 到 60 毫秒，与成功的回声抑制相关的增强伽马波段相位同步（峰值约为 40 Hz）是明显的。N1 潜伏期为空间移位提供了一个分类的神经标记，而 N1 振幅仍反映了第二个（滞后）点击的物理存在。这些结果提供了证据，表明（1）回声抑制很早就开始了，最晚在声音信号首次到达皮层时开始，（2）大脑在主要声音捕获之前就将感知到的回声进行了空间移位。
