Early exploration of innovative AEP-Tests for hidden hearing loss

Project Goals

Early signs of hearing loss usually involve speech-comprehension difficulties in noisy environments with no discernible alteration in audiometric results – the audiometry is the gold-standard method for measuring hearing loss and consist of estimating the lowest hearing level at different frequencies. This form of hearing problem is known as hidden hearing loss (HHL) – hidden because it is not possible to diagnose using best-practice clinical tools, such as the audiogram. In fact, one person for every ten who visit a hearing clinic reporting hearing-in-noise difficulties cannot be helped because the nature of their hearing difficulties cannot be determined.

Studies conducted in animals provide a model of different neurophysiological pathologies that could be involved in HHL in humans, however research in humans remains inconclusive, and no significant progress has been made in the past 10 years. This project aimed to design and demonstrate the feasibility of three novel tests based on auditory evoked potentials (AEPs) – signals recorded from the brain that are associated with the activity of the neurons in response to sounds. The main advantage of using AEP methodologies is that they are independent from a person’s subjectivity – which is why these methods are known as objective. The three novel tests proposed in this project included:

• Test 1. A comprehensive measure of the neural activity from all the auditory pathway – from the inner ear to the brain. This extends existing methods that only provide the neural response to portions of the auditory pathway.
• Test 2. An objective measure of binaural hearing performance. Existing methods measuring binaural hearing are unreliable. In contrast, the novel test of this project will provide reliable responses sensitive to binaural hearing.
• Test 3. A test that measures the brain response to natural speech which can be used to evaluate cognitive processes such as selective attention – critical for understanding speech in noisy venues.

Results & Significance

• Test 1. Results demonstrated that it is feasible to obtain the combined neural response across the auditory pathway using stimuli that assess isolated portions of the human cochlea. The new biomarkers of this test could increase sensitivity to early signs of hearing loss which to date are undetected. Further, the novel representation of this signals has potential to transform the way that these signals are recorded and analysed in clinical environments.
• Test 2. Results showed that the brain signals recorded in this test are sensitive to binaural hearing performance, and that their magnitude correlates with a behavioural speech-in-noise test. This points out that these novel biomarkers could be sensitive to binaural hearing difficulties expected in individuals with normal audiograms who struggle keeping a conversation in a noisy place.
• Test 3. Results showed that (1) it is feasible to record the brain signal evoked by a complex stimulus such as real running speech, and that (2) the recorded response is sensitive to selective attention. This novel biomarker has a strong potential to characterise hearing-in-noise difficulties and to evaluate the benefit of assistive technologies such as hearing aids and hearables.