Department of Otorhinolaryngology/Head and Neck Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Research School of Behavioral and Cognitive Neurosciences, Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands.
Ear Hear. 2019 Jan/Feb;40(1):63-76. doi: 10.1097/AUD.0000000000000591.
Real-life, adverse listening conditions involve a great deal of speech variability, including variability in speaking style. Depending on the speaking context, talkers may use a more casual, reduced speaking style or a more formal, careful speaking style. Attending to fine-grained acoustic-phonetic details characterizing different speaking styles facilitates the perception of the speaking style used by the talker. These acoustic-phonetic cues are poorly encoded in cochlear implants (CIs), potentially rendering the discrimination of speaking style difficult. As a first step to characterizing CI perception of real-life speech forms, the present study investigated the perception of different speaking styles in normal-hearing (NH) listeners with and without CI simulation.
The discrimination of three speaking styles (conversational reduced speech, speech from retold stories, and carefully read speech) was assessed using a speaking style discrimination task in two experiments. NH listeners classified sentence-length utterances, produced in one of the three styles, as either formal (careful) or informal (conversational). Utterances were presented with unmodified speaking rates in experiment 1 (31 NH, young adult Dutch speakers) and with modified speaking rates set to the average rate across all utterances in experiment 2 (28 NH, young adult Dutch speakers). In both experiments, acoustic noise-vocoder simulations of CIs were used to produce 12-channel (CI-12) and 4-channel (CI-4) vocoder simulation conditions, in addition to a no-simulation condition without CI simulation.
In both experiments 1 and 2, NH listeners were able to reliably discriminate the speaking styles without CI simulation. However, this ability was reduced under CI simulation. In experiment 1, participants showed poor discrimination of speaking styles under CI simulation. Listeners used speaking rate as a cue to make their judgements, even though it was not a reliable cue to speaking style in the study materials. In experiment 2, without differences in speaking rate among speaking styles, listeners showed better discrimination of speaking styles under CI simulation, using additional cues to complete the task.
The findings from the present study demonstrate that perceiving differences in three speaking styles under CI simulation is a difficult task because some important cues to speaking style are not fully available in these conditions. While some cues like speaking rate are available, this information alone may not always be a reliable indicator of a particular speaking style. Some other reliable speaking styles cues, such as degraded acoustic-phonetic information and variability in speaking rate within an utterance, may be available but less salient. However, as in experiment 2, listeners' perception of speaking styles may be modified if they are constrained or trained to use these additional cues, which were more reliable in the context of the present study. Taken together, these results suggest that dealing with speech variability in real-life listening conditions may be a challenge for CI users.
现实生活中的不利听力条件涉及到大量的言语可变性，包括说话风格的可变性。根据说话的情境，说话者可能会使用更随意、更简洁的说话方式，或者更正式、更谨慎的说话方式。关注描述不同说话风格的细微的声学语音细节有助于感知说话者使用的说话风格。这些声学语音线索在人工耳蜗（CI）中编码较差，可能会使说话风格的区分变得困难。作为对现实生活中言语形式的 CI 感知进行特征描述的第一步，本研究调查了正常听力（NH）听众在有无 CI 模拟的情况下对不同说话风格的感知。
在两个实验中，使用说话风格辨别任务来评估三种说话风格（会话中简化的言语、复述故事中的言语和仔细阅读的言语）的辨别。NH 听众将以三种风格之一产生的句子长度的话语分类为正式（谨慎）或非正式（会话）。在实验 1 中，以未修改的说话率呈现话语（31 名 NH，年轻成年荷兰语说话者），在实验 2 中，以所有话语的平均率设置为修改后的说话率（28 名 NH，年轻成年荷兰语说话者）。在这两个实验中，除了没有 CI 模拟的情况下的无模拟条件外，还使用了 CI-12 和 CI-4 声码器模拟条件的声学噪声声码器模拟。
在实验 1 和实验 2 中，NH 听众无需 CI 模拟即可可靠地区分说话风格。然而，在 CI 模拟下，这种能力会降低。在实验 1 中，参与者在 CI 模拟下的说话风格辨别能力较差。参与者使用说话率作为判断依据，尽管在研究材料中，它不是说话风格的可靠依据。在实验 2 中，由于说话风格之间的说话率没有差异，因此听众在 CI 模拟下使用其他线索来完成任务，从而更好地辨别说话风格。
本研究的结果表明，在 CI 模拟下感知三种说话风格的差异是一项困难的任务，因为有些重要的说话风格线索在这些条件下无法完全获得。虽然有些线索（如说话率）是可用的，但单凭这些信息并不总是特定说话风格的可靠指标。其他一些可靠的说话风格线索，例如语音信息的降级和话语内说话率的变化，可能是可用的，但不太明显。然而，正如实验 2 所示，如果听众受到约束或接受使用这些额外线索的训练，他们对说话风格的感知可能会发生变化，这些线索在本研究的背景下更为可靠。总的来说，这些结果表明，在现实生活中的听力条件下处理言语可变性可能是 CI 用户的一个挑战。
