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

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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.