Alickovic Emina, Ng Elaine Hoi Ning, Fiedler Lorenz, Santurette Sébastien, Innes-Brown Hamish, Graversen Carina
Eriksholm Research Centre, Oticon A/S, Snekkersten, Denmark.
Department of Electrical Engineering, Linkoping University, Linkoping, Sweden.
Front Neurosci. 2021 Mar 26;15:636060. doi: 10.3389/fnins.2021.636060. eCollection 2021.
Previous research using non-invasive (magnetoencephalography, MEG) and invasive (electrocorticography, ECoG) neural recordings has demonstrated the progressive and hierarchical representation and processing of complex multi-talker auditory scenes in the auditory cortex. Early responses (<85 ms) in primary-like areas appear to represent the individual talkers with almost equal fidelity and are independent of attention in normal-hearing (NH) listeners. However, late responses (>85 ms) in higher-order non-primary areas selectively represent the attended talker with significantly higher fidelity than unattended talkers in NH and hearing-impaired (HI) listeners. Motivated by these findings, the objective of this study was to investigate the effect of a noise reduction scheme (NR) in a commercial hearing aid (HA) on the representation of complex multi-talker auditory scenes in distinct hierarchical stages of the auditory cortex by using high-density electroencephalography (EEG).
We addressed this issue by investigating early (<85 ms) and late (>85 ms) EEG responses recorded in 34 HI subjects fitted with HAs. The HA noise reduction (NR) was either on or off while the participants listened to a complex auditory scene. Participants were instructed to attend to one of two simultaneous talkers in the foreground while multi-talker babble noise played in the background (+3 dB SNR). After each trial, a two-choice question about the content of the attended speech was presented.
Using a stimulus reconstruction approach, our results suggest that the attention-related enhancement of neural representations of target and masker talkers located in the foreground, as well as suppression of the background noise in distinct hierarchical stages is significantly affected by the NR scheme. We found that the NR scheme contributed to the enhancement of the foreground and of the entire acoustic scene in the early responses, and that this enhancement was driven by better representation of the target speech. We found that the target talker in HI listeners was selectively represented in late responses. We found that use of the NR scheme resulted in enhanced representations of the target and masker speech in the foreground and a suppressed representation of the noise in the background in late responses. We found a significant effect of EEG time window on the strengths of the cortical representation of the target and masker.
Together, our analyses of the early and late responses obtained from HI listeners support the existing view of hierarchical processing in the auditory cortex. Our findings demonstrate the benefits of a NR scheme on the representation of complex multi-talker auditory scenes in different areas of the auditory cortex in HI listeners.
以往使用非侵入性（脑磁图，MEG）和侵入性（皮层脑电图，ECoG）神经记录的研究表明，听觉皮层中复杂多说话者听觉场景的表征和处理是渐进且分层的。初级样区域中的早期反应（<85毫秒）似乎以几乎相同的保真度表征各个说话者，并且在听力正常（NH）的听众中与注意力无关。然而，在高阶非初级区域中的晚期反应（>85毫秒）在NH和听力受损（HI）的听众中，选择性地表征被关注的说话者，其保真度明显高于未被关注的说话者。受这些发现的启发，本研究的目的是通过使用高密度脑电图（EEG）来研究商业助听器（HA）中的降噪方案（NR）对听觉皮层不同分层阶段中复杂多说话者听觉场景表征的影响。
我们通过研究34名佩戴HA的HI受试者记录的早期（<85毫秒）和晚期（>85毫秒）EEG反应来解决这个问题。当参与者聆听复杂听觉场景时，HA的降噪（NR）处于开启或关闭状态。参与者被指示在背景中播放多说话者嘈杂声（+3 dB信噪比）时，关注前景中同时出现的两个说话者之一。每次试验后，会提出一个关于被关注语音内容的二选一问题。
使用刺激重建方法，我们的结果表明，位于前景中的目标和掩蔽说话者的神经表征与注意力相关的增强，以及在不同分层阶段对背景噪声的抑制，均受到NR方案的显著影响。我们发现NR方案有助于在早期反应中增强前景和整个声学场景，并且这种增强是由目标语音的更好表征驱动的。我们发现HI听众中的目标说话者在晚期反应中被选择性地表征。我们发现使用NR方案会导致在晚期反应中增强前景中目标和掩蔽语音的表征，并抑制背景中噪声的表征。我们发现EEG时间窗口对目标和掩蔽的皮层表征强度有显著影响。
总之，我们对HI听众早期和晚期反应的分析支持了听觉皮层分层处理的现有观点。我们的研究结果证明了NR方案对HI听众听觉皮层不同区域中复杂多说话者听觉场景表征的益处。
