The fly: an insect with a “rocker” for unique hearing
They possess one of the most accurate and efficient hearing systems in the animal kingdom, and the precision with which the fly species Ormia ochracea can localize sources of sound is unparalleled – which is why researchers are trying to reverse engineer its hearing apparatus with a view to helping people affected by hearing loss.
Things can get pretty loud in the natural world – for flies’ ears at least. The fly species Ormia ochracea is nonetheless able to locate exactly where a cricket’s chirping is coming from, for example, and researchers at the University of Texas have discovered that it is a flexible “rocker” in the insect’s head that allows it to do this. When a sound wave hits the seesaw-shaped membrane, it deforms and tips to one side, allowing the fly to positively identify a cricket’s chirping – and where it is coming from.
This precise localization is unique in the animal kingdom – although the fly’s hearing organs are positioned only half a millimeter apart, they can pinpoint the direction of a sound to within two degrees. This is all the more astounding when you consider how directional hearing usually works: the brain registers how much later a sound reaches the eardrum located further away from the source, and how great the difference in volume is from ear to ear. To achieve this, however, there has to be a certain spacing between the two receptors: sound pressure diminishes with distance. “In principle, a fly’s ear is a clever directional microphone,” explains Stefan Launer, Sonova’s Senior Vice President Science & Technology and an audiological research expert.
The process described above could, if replicated successfully, benefit people with hearing loss, as it could be deployed to help them filter out significant sounds – such as a voice for example – from background noise. “The problem is that a fly’s ear is constructed for a higher frequency range than we use for a hearing aid, so we are investigating how the principle and the mechanism might be adapted and transposed to the correct frequency band.” While Launer concedes that the mode of operation cannot be transferred directly to humans, he says: “It certainly makes sense to attempt to understand such systems. Doing so is genuinely inspiring and prompts you to think about things in entirely new ways.”
Discreet and effective methods for hearing aid wearers to focus voices already exist – Phonak’s Roger Pen, for example. A wireless microphone for use at work or home, the Roger Pen offers optimal speech comprehension in noise and over distance, plus Bluetooth connectivity.