Part 1: Binaural Hearing in Single-Sided Deafness

For many years, physicist Dr Reinhold Schatzer has been researching the audiological fundamentals of hearing and implantable hearing systems, with a focus on single-sided deafness (SSD).
In this expert interview, he explains the challenges that people with single-sided deafness face and how SSD impacts their quality of life.
Reinhold Schatzer is a Senior Research Engineer at MED-EL and an expert in sound coding and signal processing.

HB: Dr Schatzer, you have been working on single-sided deafness (SSD) for many years. What are the biggest challenges in everyday life for people living with this condition?
RS: Single-sided deafness, i.e. one ear with severe hearing loss and the other with no hearing loss, leads to a number of limitations, especially in sound localization and speech understanding in noise. Patients need more listening effort and attention, and tire more quickly.

HB: Let us take a brief look at the basics: What happens in binaural hearing?
RS: In binaural hearing, the brain combines signals from both ears. SSD patients do not have this binaural loudness summation. They need a higher sound pressure level, i.e. more dB, to perceive the same loudness as individuals with normal hearing in both ears. Hearing soft sounds becomes more difficult.

HB: How does SSD affect directional hearing?
RS: For sound localisation, our brain uses interaural time differences (ITD) and interaural level differences (ILD) between both ears. In case of single-sided deafness, this information is missing, resulting in limited spatial orientation.

HB: How does monaural hearing affect speech understanding?
RS: Patients with SSD have significantly poorer speech understanding in noisy environments. This is caused by two effects: first, the head shadow effect, where our head acts as an acoustic barrier. If the sound signal reaches the deaf ear, the head attenuates transmission to the normal-hearing ear, worsening the signal-to-noise ratio. The second reason is a lack of binaural noise reduction, where the brain uses redundancy from both ears to filter out noise. These deficits make speech understanding in noisy environments much more difficult for SSD patients.

HB: Bone conduction hearing systems are often used to treat SSD. How are the outcomes?
RS: Systems like CROS or BAHA transmit sound from the deaf ear to the normal-hearing ear. However, they do not deliver real binaural hearing. They also do not alleviate tinnitus in the deaf ear, which often occurs as a side effect in SSD patients, further reducing their quality of life.

About the expert:
Dr Reinhold Schatzer is a Senior Research Engineer at MED-EL and an expert in sound coding and signal processing.

*Disclaimer: Cochlear implants for single-sided deafness may not be reimbursed in every country; please check whether they are covered by the healthcare or insurance system in your country of residence.