New Technologies and Applications using the Speech-evoked Frequency Following Response

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Hearing impairment is an important health problem in Canada, and there is a need to develop improved technologies to objectively evaluate hearing. When sound reaches the ear, small electrical pulses propagate through the auditory centers in the brain, eventually resulting in the sensation of hearing. Much about this process is not well-understood, but by placing surface electrodes on the scalp we can non-invasively record the electrical activity originating in these auditory centers. In particular, it is possible to record auditory brainstem responses, which allow audiologists to diagnose hearing problems and locate their origin in the brain. The sound that audiologists most commonly use for this test is a brief loud click. However, a click does not provide sufficient information to allow assessing the ability to hear speech. As a result, there is increasing interest in recording the brain's electrical responses that follow the temporal and frequency patterns of speech. Recently, our group has recorded Speech-evoked Frequency Following Responses (sFFRs) with natural and synthetic speech stimuli, and we have shown that these responses can provide an important window into auditory processing of speech. The sFFR is so similar to the speech waveform, that if it is converted to a sound and played back, it is perceived as intelligible speech. This means that this signal 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 techniques to detect the sFFR that are inspired by speech enhancement algorithms developed for noisy communication environments. Moreover, because the sFFR has been recorded in response to a limited set of speech stimuli, experimental and theoretical work will be performed with listeners who have normal hearing to clarify the basic properties of the responses, with a diverse set of speech samples and in different realistic acoustic environments. A new brain-computer interface technology based on the sFFR will also be developed to automatically optimize hearing aid fitting, which is often a challenging task. The proposed research program is expected to have a significant impact in the field of Biomedical Engineering and on hearing assistive technologies. Novel techniques for the assessment of hearing function will be developed, including new signal processing algorithms and instrumentation for detecting speech-evoked responses, improved models of human auditory processing of speech, and new technologies for objective hearing aid fitting. Moreover, Doctoral and Master's students will be trained in interdisciplinary and collaborative research, and so will develop skills of value to the Canadian biomedical and hearing devices industries, the hearing and speech research communities, and healthcare.