Measurement and Applications of Speech-evoked Auditory Brainstem Responses (sABRs)

当声音到达耳朵时，微小的电脉冲通过大脑中不同的听觉中心传播，从而产生听觉。尽管这个过程仍然是个谜，但通过将表面电极贴在头皮上，我们可以无创地记录这些听觉中心的电活动。特别是，可以记录大脑深处产生的听觉脑干反应。这些反应使临床医生能够诊断听力问题并确定其在大脑中的起源。临床医生在这个测试中最常用的声音是一个简短的响亮的咔哒声，它的好处是作为一个简单的刺激，有一个明确的诱发反应。然而，点击声并不能提供足够的信息来让我们评估听到语音的能力。因此，人们对开发记录大脑对语言的电反应的测试越来越感兴趣。最近，我们的研究小组记录了自然和合成语音刺激下的语音诱发听觉脑干反应（sABRs），并表明这些反应可以为正常和听力受损个体的语音听觉加工提供一个重要的窗口。例如，我们已经表明，sABR密切关注元音音高的细微变化。事实上，这种大脑信号与语音波形非常相似，如果将其转换为声音并回放，就会被认为是可理解的语音。这意味着它允许我们“偷听”大脑内部的语言表达。

When sound reaches the ear, tiny electrical pulses propagate through the different auditory centers in the brain, resulting in the sensation of hearing. Although much about this process remains a mystery, by taping surface electrodes to the scalp we can non-invasively record the electrical activity in these auditory centers. In particular, it is possible to record auditory brainstem responses, which are generated deep within the brain. These responses allow clinicians to diagnose hearing problems and locate their origin in the brain. The sound that clinicians most commonly use for this test is a brief loud click, which has the benefit of being a simple stimulus with a well-defined evoked response. However, a click does not provide sufficient information to allow us to assess the ability to hear speech. As a result, there is increasing interest in developing tests that record the brain's electrical response to speech. Recently, our group has recorded Speech-evoked Auditory Brainstem Responses (sABRs) with natural and synthetic speech stimuli, and we have shown that these responses can provide an important window into auditory processing of speech in normal and hearing impaired individuals. For example, we have shown that the sABR closely follows the fine variations in the pitch of a vowel. In fact, this brain signal is so similar to the speech waveform, if it is converted to a sound and played back, it is perceived as intelligible speech. This means that it allows us to "listen in" on the internal representation of speech within the brain. One impediment to progress in this field has been that excessive recording times are often required. The proposed research program aims to develop more efficient methods to detect the sABR that are inspired by speech enhancement algorithms developed for noisy communication environments. Moreover, because the sABR has been recorded in response to a limited set of speech stimuli, experimental and theoretical work will be performed to clarify the basic properties of the responses, with a diverse set of speech samples and in different acoustic environments. The measurement of sABRs will also be used to determine the impact of hearing aids on the internal representation of the speech signal. This is expected to provide a powerful objective tool for improving hearing aid fitting, which is important for optimising hearing aid performance. The proposed research program is expected to have a significant impact in the fields of Biomedical Engineering and Audiology. Novel techniques for the assessment and treatment of hearing impairment - an important health problem in Canada - will be developed, including improved models of human auditory processing of speech, new signal processing algorithms for speech-evoked responses, and instrumentation for measuring these responses and applying them for hearing aid fitting. Moreover, Doctoral and Master’s students will be trained in interdisciplinary research spanning engineering and audiology, and will develop skills of value to the Canadian biomedical and hearing assistive devices industries, healthcare, and the hearing and speech research communities.