1 Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, NJ, USA.
2 Graduate School of Biomedical Sciences, Rutgers University, Newark, NJ, USA.
Trends Hear. 2018 Jan-Dec;22:2331216518817464. doi: 10.1177/2331216518817464.
Informational masking (IM) can greatly reduce speech intelligibility, but the neural mechanisms underlying IM are not understood. Binaural differences between target and masker can improve speech perception. In general, improvement in masked speech intelligibility due to provision of spatial cues is called spatial release from masking. Here, we focused on an aspect of spatial release from masking, specifically, the role of spatial attention. We hypothesized that in a situation with IM background sound (a) attention to speech recruits lateral frontal cortex (LFCx) and (b) LFCx activity varies with direction of spatial attention. Using functional near infrared spectroscopy, we assessed LFCx activity bilaterally in normal-hearing listeners. In Experiment 1, two talkers were simultaneously presented. Listeners either attended to the target talker (speech task) or they listened passively to an unintelligible, scrambled version of the acoustic mixture (control task). Target and masker differed in pitch and interaural time difference (ITD). Relative to the passive control, LFCx activity increased during attentive listening. Experiment 2 measured how LFCx activity varied with ITD, by testing listeners on the speech task in Experiment 1, except that talkers either were spatially separated by ITD or colocated. Results show that directing of auditory attention activates LFCx bilaterally. Moreover, right LFCx is recruited more strongly in the spatially separated as compared with colocated configurations. Findings hint that LFCx function contributes to spatial release from masking in situations with IM.
信息掩蔽（IM）会极大地降低语音的可懂度，但 IM 背后的神经机制尚不清楚。目标和掩蔽之间的双耳差异可以提高语音感知。一般来说，由于提供空间线索而导致的掩蔽语音可懂度的提高称为掩蔽释放。在这里，我们关注掩蔽释放的一个方面，即空间注意的作用。我们假设在存在 IM 背景声音的情况下（a）注意言语会募集外侧额前皮质（LFCx），（b）LFCx 活动随空间注意方向而变化。我们使用功能性近红外光谱技术，双侧评估正常听力听众的 LFCx 活动。在实验 1 中，同时呈现两个说话者。听众要么专注于目标说话者（言语任务），要么被动地听声音混合物的无法理解的乱序版本（控制任务）。目标和掩蔽在音调和两耳时间差（ITD）上有所不同。与被动控制相比，在专注聆听时，LFCx 活动增加。实验 2 通过在实验 1 中的言语任务中测试听众，测量 LFCx 活动如何随 ITD 而变化，只是说话者在空间上通过 ITD 分开或共置。结果表明，听觉注意力的引导会双侧激活 LFCx。此外，与共置配置相比，在空间分离的情况下，右侧 LFCx 的募集更强。这些发现表明，在存在 IM 的情况下，LFCx 功能有助于掩蔽释放。
