Watching the lips of a speaker enhances speech perception. At the same time, the 100 ms response to speech sounds is suppressed in the observer's auditory cortex. Here, we used whole-scalp 306-channel magnetoencephalography (MEG) to study whether lipreading modulates human auditory processing already at the level of the most elementary sound features, i.e., pure tones. We further envisioned the temporal dynamics of the suppression to tell whether the effect is driven by top-down influences. Nineteen subjects were presented with 50 ms tones spanning six octaves (125–8000 Hz) (1) during “lipreading,” i.e., when they watched video clips of silent articulations of Finnish vowels /a/, /i/, /o/, and /y/, and reacted to vowels presented twice in a row; (2) during a visual control task; (3) during a still-face passive control condition; and (4) in a separate experiment with a subset of nine subjects, during covert production of the same vowels. Auditory-cortex 100 ms responses (N100m) were equally suppressed in the lipreading and covert-speech-production tasks compared with the visual control and baseline tasks; the effects involved all frequencies and were most prominent in the left hemisphere. Responses to tones presented at different times with respect to the onset of the visual articulation showed significantly increased N100m suppression immediately after the articulatory gesture. These findings suggest that the lipreading-related suppression in the auditory cortex is caused by top-down influences, possibly by an efference copy from the speech-production system, generated during both own speech and lipreading.
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机译:看着说话者的嘴唇可以增强语音感知能力。同时,观察者的听觉皮层对语音的100 ms响应被抑制。在这里,我们使用全头皮306通道脑磁图(MEG)来研究唇读是否已经在最基本的声音特征(即纯音)水平上调节了人类听觉处理。我们进一步设想了抑制的时间动态,以判断该影响是否由自上而下的影响所驱动。在“唇读”期间,即当他们观看芬兰语元音/ a /,/ i /,/ o /的无声发音的视频剪辑时,向19个主题展示了跨越6个八度音阶(125-8000 Hz)(1)的50 ms音调。和/ y /,并对连续出现两次的元音作出反应; (2)在视觉控制任务中; (3)在静止的被动控制状态下; (4)在一个秘密实验中,由9名受试者组成的子集,在相同的元音的秘密产生过程中。与视觉控制和基线任务相比,在唇读和秘密语音制作任务中听觉皮层100 ms响应(N100m)受到同等抑制;这些影响涉及所有频率,并且在左半球最明显。在视觉连接开始后,对在不同时间出现的音调的响应显示,N100m抑制立即显着增加。这些发现表明,在听觉皮层中与唇读相关的抑制是由自上而下的影响引起的,可能是由自己的语音和唇读期间产生的来自语音产生系统的有效拷贝引起的。
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