Chair of Cognitive and Clinical Neuroscience, Faculty of Psychology, Technische Universität Dresden, Dresden 01187, Germany.
Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig 04103, Germany.
J Neurosci. 2021 Aug 18;41(33):7136-7147. doi: 10.1523/JNEUROSCI.2902-20.2021. Epub 2021 Jul 9.
Recognizing speech in background noise is a strenuous daily activity, yet most humans can master it. An explanation of how the human brain deals with such sensory uncertainty during speech recognition is to-date missing. Previous work has shown that recognition of speech without background noise involves modulation of the auditory thalamus (medial geniculate body; MGB): there are higher responses in left MGB for speech recognition tasks that require tracking of fast-varying stimulus properties in contrast to relatively constant stimulus properties (e.g., speaker identity tasks) despite the same stimulus input. Here, we tested the hypotheses that (1) this task-dependent modulation for speech recognition increases in parallel with the sensory uncertainty in the speech signal, i.e., the amount of background noise; and that (2) this increase is present in the ventral MGB, which corresponds to the primary sensory part of the auditory thalamus. In accordance with our hypothesis, we show, by using ultra-high-resolution functional magnetic resonance imaging (fMRI) in male and female human participants, that the task-dependent modulation of the left ventral MGB (vMGB) for speech is particularly strong when recognizing speech in noisy listening conditions in contrast to situations where the speech signal is clear. The results imply that speech in noise recognition is supported by modifications at the level of the subcortical sensory pathway providing driving input to the auditory cortex. Speech recognition in noisy environments is a challenging everyday task. One reason why humans can master this task is the recruitment of additional cognitive resources as reflected in recruitment of non-language cerebral cortex areas. Here, we show that also modulation in the primary sensory pathway is specifically involved in speech in noise recognition. We found that the left primary sensory thalamus (ventral medial geniculate body; vMGB) is more involved when recognizing speech signals as opposed to a control task (speaker identity recognition) when heard in background noise versus when the noise was absent. This finding implies that the brain optimizes sensory processing in subcortical sensory pathway structures in a task-specific manner to deal with speech recognition in noisy environments.
在背景噪声中识别语音是一项艰巨的日常活动，但大多数人都能掌握它。迄今为止，对于人类大脑在语音识别过程中如何应对这种感官不确定性，还没有解释。以前的工作表明，在没有背景噪声的情况下识别语音涉及听觉丘脑（内侧膝状体；MGB）的调制：在需要跟踪快速变化的刺激特性的语音识别任务中，左 MGB 的反应更高，与相对恒定的刺激特性（例如，说话者身份任务）相比，尽管输入相同的刺激。在这里，我们测试了以下假设：（1）这种依赖于任务的调制随着语音信号中的感官不确定性（即背景噪声的数量）而平行增加；（2）这种增加存在于腹侧 MGB 中，与听觉丘脑的初级感觉部分相对应。根据我们的假设，我们通过使用男性和女性人类参与者的超高分辨率功能磁共振成像（fMRI）显示，当在嘈杂的听力条件下识别语音时，左腹侧 MGB（vMGB）对语音的任务依赖性调制特别强烈，与语音信号清晰的情况相比。结果表明，噪声中的语音识别得到了下丘体感通路水平的修改的支持，该修改为听觉皮层提供了驱动输入。在嘈杂环境中识别语音是一项具有挑战性的日常任务。人类能够掌握这项任务的一个原因是，由于涉及到非语言大脑皮层区域的招募，因此会招募额外的认知资源。在这里，我们表明，初级感觉通路的调制也特别参与了噪声中的语音识别。我们发现，当在背景噪声中而不是在没有噪声的情况下听到语音信号时，相对于控制任务（说话者身份识别），左初级感觉丘脑（腹侧内侧膝状体；vMGB）的参与度更高。这一发现意味着大脑以特定于任务的方式优化了下丘体感通路结构中的感官处理，以应对嘈杂环境中的语音识别。
