People with fully-functioning hearing are able to precisely estimate where a sound is coming from, even with their eyes closed. Sound coming from the right enters the right ear first, and the left ear later. The difference in time is registered by our brain, which allows us to determine where the sound is coming from. This is very difficult for people who use hearing aids or implants, because the current systems are not able to localise sound. This makes it difficult for people with a hearing aid to engage in conversations in a busy environment: they aren’t able to hear where each sound is coming from.
On a team day, neuroscientist Martijn Agterberg attended a presentation of beekeeper Marius Woensdrecht where he realised that bees are probably able to locate sound. Agterberg: “Marius talked about bees being able to hear. I asked where the ears are located. They turned out to be located on antennas that the bees can move. I thought: ‘That has a reason, maybe it’s a mechanism to locate sound’.”
The distance between bees’ ears is so small that they cannot deduce where the sound is coming from using a difference in time. And bees don’t have the nicely shaped auricle that humans have, which helps us analyse whether sound is coming from above or below. Apparently, bees locate sounds in a different way than humans. Agterberg theorised that bees are able to move their ears to determine where sounds are coming from. In 2020, Agterberg was given the chance to study this with a NWO Open Mind grant.
“I promptly found an article by Harvard researchers written in 2019. The article itself is about the Drosophila, a fruit fly. By moving its ears, the Drosophila generates its own Doppler-effect. They are able to scan for this and determine where the sound is coming from. Brilliant but very simple at the same time.”
Hearing implants: 5 to 10 times better
The idea for applying this to a better hearing implant can quickly: if the directional sensitivity of the implants can be improved, the quality of hearing can be improved for hearing-impaired people. Agterberg: “By using a directivity sensor in the microphone in implants, you could potentially be able to better determine where the sound is coming from with one implant only, and process the sound much more efficiently in the sound processor. This allows people to keep up with conversations in surroundings with a lot of background noise. With an improved sound processor, you’re able to better understand speech in complex listening situations than when you’re listening with two implants.” Agterberg built a prototype with a NWO Take-off grant and it worked: the prototype has a so-called ‘beam shaper’ that’s 5 to 10 times better, making the prototype 5 to 10 times better than the current hearing implants.