Quirks & Quarks

Your eardrums are pointing where your eyes are looking

Scientists think this discovery could lead to improved hearing aid design.
Eye movements can affect the signals in auditory areas of the brain. (Pixabay)

The experiment

Imagine yourself sitting down, head still, and moving your eyes around. You likely don't feel any other part of your head moving, but a new study suggests that wherever your eyes go, your eardrums follow. 

Dr. Jennifer Groh is a professor in the departments of neurobiology and of psychology and neuroscience at Duke University in Durham, N.C.

"We had previously done experiments measuring signals in the brain. And we knew from those experiments that eye movements can affect the signals in auditory areas of the brain. So that motivated us to then ask, 'Where's the first point in the process of hearing that eye movements affect what is happening?" asks Groh.

Groh and her colleagues put microphones in the ear canals of test subjects to pick up the sounds the ear was making. Then they had subjects wear an eye tracker and instructed them to move their eyes around. 

"What the microphones are picking up is any kind of sound that is generated from within the ear itself," says Groh. The brain makes the eardrums move by pulling and pushing on the bones in the middle ear, and this makes a noise the microphones can detect. With the information from the microphone in the ear and the eye tracker, they can determine how the ears move in relation to the eyes. 

The discovery

"We found that the eye movements were accompanied by little sounds that the eardrums were making. There was a little vibration in the eardrum. The amount of the vibration depended on how big the eye movement was," says Groh. "And the direction eardrum movement varied with the direction of the eye movement." 

The eyes and eardrums move in sync. (Jessi Cruger and David Murphy/ Duke University)

She says it's possible the eyes are telling the ears where to listen. But she also says it's possible this is affecting the entire auditory scene the brain is stitching together with the the visual input from our eyes. 

A better hearing aid

One of the challenges for those who are hearing impaired and require a hearing aid is that the hearing aids often amplify all the sounds around, making it difficult to focus on what they really want to hear.

Groh says: "What these people really need is to have the sound amplified selectively for the things they're paying attention to. It's hard for a mechanical device to do that because it doesn't have these mechanisms that the brain uses for tailoring its own input. So I think if some eye movement sensing, some eye-tracking, could be incorporated into hearing aids and used to amplify sounds coming from particular directions, that would be a helpful innovation."