Department of Otolaryngology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR, 97239, USA.
National Center for Rehabilitative Auditory Research, VA Portland Health Care System, 3710 SW US Veterans Road, Portland, OR, 97239, USA.
J Assoc Res Otolaryngol. 2021 Jul;22(4):443-461. doi: 10.1007/s10162-021-00790-7. Epub 2021 Apr 20.
Normal-hearing (NH) listeners use frequency cues, such as fundamental frequency (voice pitch), to segregate sounds into discrete auditory streams. However, many hearing-impaired (HI) individuals have abnormally broad binaural pitch fusion which leads to fusion and averaging of the original monaural pitches into the same stream instead of segregating the two streams (Oh and Reiss, 2017) and may similarly lead to fusion and averaging of speech streams across ears. In this study, using dichotic speech stimuli, we examined the relationship between speech fusion and vowel identification. Dichotic vowel perception was measured in NH and HI listeners, with across-ear fundamental frequency differences varied. Synthetic vowels /i/, /u/, /a/, and /ae/ were generated with three fundamental frequencies (F) of 106.9, 151.2, and 201.8 Hz and presented dichotically through headphones. For HI listeners, stimuli were shaped according to NAL-NL2 prescriptive targets. Although the dichotic vowels presented were always different across ears, listeners were not informed that there were no single vowel trials and could identify one vowel or two different vowels on each trial. When there was no F difference between the ears, both NH and HI listeners were more likely to fuse the vowels and identify only one vowel. As ΔF increased, NH listeners increased the percentage of two-vowel responses, but HI listeners were more likely to continue to fuse vowels even with large ΔF. Binaural tone fusion range was significantly correlated with vowel fusion rates in both NH and HI listeners. Confusion patterns with dichotic vowels differed from those seen with concurrent monaural vowels, suggesting different mechanisms behind the errors. Together, the findings suggest that broad fusion leads to spectral blending across ears, even for different ΔF, and may hinder the stream segregation and understanding of speech in the presence of competing talkers.
正常听力 (NH) 者使用频率线索,如基频 (音高),将声音分离成离散的听觉流。然而,许多听力受损 (HI) 个体的双耳音调融合异常宽阔,导致原始单耳音高融合并平均分配到同一流中,而不是将两个流分离 (Oh 和 Reiss,2017),并且可能类似地导致双耳之间的语音流融合和平均分配。在这项研究中,我们使用双音节语音刺激,研究了语音融合与元音识别之间的关系。在 NH 和 HI 者中测量了双音节元音感知,跨耳基频差异变化。使用三个基频 (F) 为 106.9、151.2 和 201.8 Hz 的合成元音 /i/、/u/、/a/ 和 /ae/,通过耳机呈现双音节。对于 HI 者,刺激根据 NAL-NL2 处方目标进行塑形。尽管呈现的双音节元音在双耳之间始终不同,但者没有被告知没有单个元音试验,并且可以在每个试验中识别一个元音或两个不同的元音。当双耳之间没有 F 差异时,NH 和 HI 者都更有可能融合元音并仅识别一个元音。随着 ΔF 的增加,NH 者增加了双元音反应的百分比,但 HI 者即使在大 ΔF 下也更有可能继续融合元音。双耳音调融合范围与 NH 和 HI 者的元音融合率显著相关。双音节元音的混淆模式与同时呈现的单音节元音不同,这表明错误背后存在不同的机制。总之,这些发现表明,宽阔的融合导致双耳之间的频谱混合,即使对于不同的 ΔF,并且可能会阻碍存在竞争说话者时的流分离和语音理解。