360 million people worldwide have some form of hearing loss, 10% of them children. While hearing aids and cochlear implants reasonably restore the hearing with the ear they supply, they do often not restore two things that normal hearing listeners take for granted: 1) Being able to localize a sound source in space and 2) being able to understand a conversation partner even in the presence of more intense competing talkers and other sound sources. Both of these abilities have been shown to contribute to the quality of life.
A sound arriving from a certain direction in space (e.g. off the midline) arrives at the two ears at slightly different times, generating an interaural time difference (ITD). In addition, the head attenuates the sound at the ear opposite to the sound source to produce an interaural level difference (ILD). Brainstem circuits are specialized in detecting ITDs and ILDs with a temporal precision unique within the nervous system. As soon as one or two hearing aids or cochlear implants are applied to the ears, any difference in their sound processing corrupts the interaural differences, reducing the binaural advantage. Further, a fair number of people that are said to be “normal hearing” in clinical terms does not get the “normal” advantage of listening with two ears – binaural hearing. This includes particularly people with a neurologic history, such as a stroke but can also happen in completely healthy individuals. To date hearing researchers can list many factors that may limit the binaural benefit. However, due to the complexity of the auditory system (a complex inner ear followed by an even more complex brain), they have only a limited understanding in which way and in which situation a certain pathology corrupts binaural hearing. Hearing devices are far from employing such causalities for optimizing algorithms to the specific pathology.
The objective of the project is therefore to better relate neurophysiology and pathophysiology to normal and impaired perception. This is done by developing a detailed computer simulation of the auditory system validated through a broad range of listening experiments. Once we are confident that we know the pathology of an individual we can then simulate this impairment and see when and how it causes the most extreme and maybe a unique problem. More though, we can develop algorithms, similar to those in hearing aids, but specific to the pathology, optimize them with the simulation and test them with the patient. If the patient shows the same improvement we have predicted in our simulation, we have not only helped the patient but demonstrated that our novel approach can potentially help hundreds of thousand people to improve their binaural hearing and hence their quality of life. Our team is thrilled to pioneer this approach and hope to trigger many follow-up studies.
