Department of Anatomy & Neurobiology, Washington University School of Medicine, St. Louis, Missouri, USA.
PLoS One. 2013;8(1):e53398. doi: 10.1371/journal.pone.0053398. Epub 2013 Jan 10.
Humans are highly adept at processing speech. Recently, it has been shown that slow temporal information in speech (i.e., the envelope of speech) is critical for speech comprehension. Furthermore, it has been found that evoked electric potentials in human cortex are correlated with the speech envelope. However, it has been unclear whether this essential linguistic feature is encoded differentially in specific regions, or whether it is represented throughout the auditory system. To answer this question, we recorded neural data with high temporal resolution directly from the cortex while human subjects listened to a spoken story. We found that the gamma activity in human auditory cortex robustly tracks the speech envelope. The effect is so marked that it is observed during a single presentation of the spoken story to each subject. The effect is stronger in regions situated relatively early in the auditory pathway (belt areas) compared to other regions involved in speech processing, including the superior temporal gyrus (STG) and the posterior inferior frontal gyrus (Broca's region). To further distinguish whether speech envelope is encoded in the auditory system as a phonological (speech-related), or instead as a more general acoustic feature, we also probed the auditory system with a melodic stimulus. We found that belt areas track melody envelope weakly, and as the only region considered. Together, our data provide the first direct electrophysiological evidence that the envelope of speech is robustly tracked in non-primary auditory cortex (belt areas in particular), and suggest that the considered higher-order regions (STG and Broca's region) partake in a more abstract linguistic analysis.
人类非常擅长处理语音。最近的研究表明，语音中的缓慢时间信息（即语音包络）对于语音理解至关重要。此外，已经发现人类皮层中的诱发电潜能与语音包络相关。然而，目前尚不清楚这种基本的语言特征是否在特定区域中以不同的方式进行编码，或者它是否在整个听觉系统中都有表示。为了回答这个问题，我们在人类受试者听口语故事时，用高时间分辨率直接从皮层记录神经数据。我们发现，人类听觉皮层中的伽马活动强烈地跟踪语音包络。这种效应非常显著，以至于在每个受试者单次呈现口语故事时都可以观察到。与涉及语音处理的其他区域（包括颞上回（STG）和后下额回（布罗卡区））相比，该效应在听觉通路中相对较早的区域（带状区域）中更为明显。为了进一步区分语音包络是否作为语音相关的音系特征（phonological），或者作为更一般的声学特征在听觉系统中进行编码，我们还使用旋律刺激来探测听觉系统。我们发现，带状区域微弱地跟踪旋律包络，并且是唯一被考虑的区域。总之，我们的数据提供了第一个直接的电生理证据，表明语音包络在非主要听觉皮层（特别是带状区域）中得到了强烈的跟踪，并表明所考虑的更高阶区域（STG 和布罗卡区）参与了更抽象的语言分析。
