New research shows that the small sounds generated within the ear by the brain contain accurate information about contemporaneous eye movements in the spatial domain: the direction and amplitude of the eye movements could be inferred from these sounds.
Lovich et al. show that eye movement-related eardrum oscillations contain parametric information about horizontal and vertical eye displacement as well as initial/final eye position with respect to the head. Image credit: Lovich et al., doi: 10.1073/pnas.2303562120.
“You can actually estimate the movement of the eyes, the position of the target that the eyes are going to look at, just from recordings made with a microphone in the ear canal,” said Duke University’s Professor Jennifer Groh, senior author of the study.
In 2018, Professor Groh and her colleagues discovered that the ears make a subtle, imperceptible noise when the eyes move.
In their new study, the researchers found that that these sounds can reveal where your eyes are looking.
Just by knowing where someone is looking, they were able to predict what the waveform of the subtle ear sound would look like.
“Since a diagonal eye movement is just a horizontal component and vertical component, we realized you can take those two components and guess what they would be if you put them together,” said first author Stephanie Lovich, a graduate student at Duke University.
“Then you can go in the opposite direction and look at an oscillation to predict that someone was looking 30 degrees to the left.”
According to the authors, these sounds may be caused when eye movements stimulate the brain to contract either middle ear muscles, which typically help dampen loud sounds, or the hair cells that help amplify quiet sounds.
“We think this is part of a system for allowing the brain to match up where sights and sounds are located, even though our eyes can move when our head and ears do not,” Professor Groh said.
Understanding the relationship between subtle ear sounds and vision might lead to the development of new clinical tests for hearing.
“If each part of the ear contributes individual rules for the eardrum signal, then they could be used as a type of clinical tool to assess which part of the anatomy in the ear is malfunctioning,” Lovich said.
The researchers are now starting to examine whether these ear sounds play a role in perception.
One set of projects is focused on how eye-movement ear sounds may be different in people with hearing or vision loss.
They are also testing whether people who don’t have hearing or vision loss will generate ear signals that can predict how well they do on a sound localization task, like spotting where an ambulance is while driving, which relies on mapping auditory information onto a visual scene.
“Some folks have a really reproducible signal day-to-day, and you can measure it quickly,” Professor Groh said.
“You might expect those folks to be really good at a visual-auditory task compared to other folks, where it’s more variable.”
The findings were published in the Proceedings of the National Academy of Sciences.
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Stephanie N. Lovich et al. 2023. Parametric information about eye movements is sent to the ears. PNAS 120 (48): e2303562120; doi: 10.1073/pnas.2303562120
