Prévost François, Lehmann Alexandre
1 Department of Speech Pathology and Audiology, McGill University Health Centre, Montreal, Quebec, Canada.
2 International Laboratory for Brain, Music & Sound Research, Montreal, Quebec, Canada.
Clin EEG Neurosci. 2018 Nov;49(6):388-397. doi: 10.1177/1550059418770051. Epub 2018 Apr 24.
Cochlear implants restore hearing in deaf individuals, but speech perception remains challenging. Poor discrimination of spectral components is thought to account for limitations of speech recognition in cochlear implant users. We investigated how combined variations of spectral components along two orthogonal dimensions can maximize neural discrimination between two vowels, as measured by mismatch negativity. Adult cochlear implant users and matched normal-hearing listeners underwent electroencephalographic event-related potentials recordings in an optimum-1 oddball paradigm. A standard /a/ vowel was delivered in an acoustic free field along with stimuli having a deviant fundamental frequency (+3 and +6 semitones), a deviant first formant making it a /i/ vowel or combined deviant fundamental frequency and first formant (+3 and +6 semitones /i/ vowels). Speech recognition was assessed with a word repetition task. An analysis of variance between both amplitude and latency of mismatch negativity elicited by each deviant vowel was performed. The strength of correlations between these parameters of mismatch negativity and speech recognition as well as participants' age was assessed. Amplitude of mismatch negativity was weaker in cochlear implant users but was maximized by variations of vowels' first formant. Latency of mismatch negativity was later in cochlear implant users and was particularly extended by variations of the fundamental frequency. Speech recognition correlated with parameters of mismatch negativity elicited by the specific variation of the first formant. This nonlinear effect of acoustic parameters on neural discrimination of vowels has implications for implant processor programming and aural rehabilitation.
人工耳蜗可恢复聋人的听力，但言语感知仍具有挑战性。人们认为，对频谱成分的辨别能力差是导致人工耳蜗使用者言语识别受限的原因。我们研究了频谱成分沿两个正交维度的组合变化如何能最大限度地提高两个元音之间的神经辨别能力，这通过失配负波来衡量。成年人工耳蜗使用者和匹配的听力正常的听众在最优-1奇偶数范式下进行脑电图事件相关电位记录。在声学自由场中呈现一个标准的/a/元音，同时呈现具有偏离基频（+3和+6半音）、使元音变为/i/的偏离第一共振峰或基频和第一共振峰同时偏离（+3和+6半音/i/元音）的刺激。通过单词重复任务评估言语识别能力。对每个偏离元音诱发的失配负波的幅度和潜伏期进行方差分析。评估失配负波的这些参数与言语识别以及参与者年龄之间的相关性强度。人工耳蜗使用者的失配负波幅度较弱，但通过元音第一共振峰的变化可使其最大化。人工耳蜗使用者的失配负波潜伏期较晚，并且基频的变化会使其显著延长。言语识别与第一共振峰特定变化诱发的失配负波参数相关。声学参数对元音神经辨别的这种非线性效应对植入处理器编程和听觉康复具有启示意义。
