Our eardrums seem to move to shift our hearing in the same direction it is looking at. It is a newly discovered curious fact for which the reason is not known .
Jennifer Groh of Duke University in Durham, North Carolina, and her team have been using microphones inserted into people’s ears to study how the eardrums act during saccades .
Saccades and eardrum
Humans do not usually look at a scene statically, but rather their eyes flick back and forth, with small movements, looking for interesting parts of a scene and building a mind map of it. These are the so-called saccades .
In the aforementioned study, 16 people were examined, detecting changes in the pressure of the ear canal that were probably caused by the muscles of the middle ear pulling on the eardrum. These pressure changes indicate that when we look to the left, for example, the left eardrum is pulled further into the ear and the one on the right ear outward, before they both move back and forth a few times.
These changes in the eardrums took place 10 milliseconds before the eyes began to move , and continued for a few tens of milliseconds after the eyes stopped.
"We believe that before actual eye movement occurs, the brain sends a signal to the ear to say ‘I have commanded the eyes to move 12 degrees to the right,’" says Groh . The movements of the eardrum that follow the change in focus can prepare our ears to hear sounds from a particular direction.
It is the first time that this movement of the eardrums synchronized with our eyes has been demonstrated. How the movement of our eardrums affects what we hear is still unclear. One theory why the eyes and ears move together in this way is that they help the brain to make sense of what we see and hear .
The discovery could lead to better hearing aids , which currently amplify all sound equally, no matter where it comes from. Just like the brain of a person with normal hearing can focus on the sound of a person you are talking to in a restaurant, while ignoring a conversation at a nearby table, a mechanism built into hearing aids that picks up signals from the eyes moving to a new location might try to amplify the sound in that particular location.