It happens even when we are completely silent.
If we move our eyes to the sides while keeping our head in a straight position, changes in the pressure of our ear canal and vibrations take place that make the eardrums also move.
What’s more, the team of neuroscientists who have noticed this assures that, surprising as it may seem, the latter occurs a few milliseconds before the eyes move , which, in their opinion, suggests that the same brain mechanism controls both things .
“In essence, it is as if the brain plans to move the eyes and, at that moment, says to itself ‘wait, the eardrums better also do it'”, explains in a statement Professor Jennifer Groh, from the departments of Psychology and Neuroscience and Neurobiology at Duke University, which has coordinated this initiative.
In an article published in the journal Proceedings of the National Academy of Sciences , the researchers, belonging to different US institutions, point out that when they examined this phenomenon in humans and in Rhesus macaques, they obtained identical results.
Scientists have long known that both eyes and ears are involved in our hearing and vision.
In fact, most people find that it is easier to understand a person if they can see them, specifically if they pay attention to their lips. However, the way the brain combines both types of information still raises many questions. Groh and his collaborators suspect that this synchrony facilitates our understanding of the environment.
A basic mechanism
In one experiment, sixteen volunteers who had been fitted with highly sensitive microphones, capable of capturing the vibrations of the eardrums, were asked to follow the evolution of an LED with their eyes. The experts found that when they moved, their eardrums moved in line with them, and that more pronounced movements also caused higher vibrations.
The point is that although the eardrums respond mainly to sounds that come from outside, the brain can also control them through small bones located in the middle ear and cells with microvilli in the cochlea, a structure of the inner ear.
This mechanism helps to modulate the intensity of sound and produces so-called otoacoustic emissions.
Now, the researchers plan to study the role this phenomenon plays in our sense of hearing and whether eye movements from top to bottom also cause these vibrations.
“These tympanic displacements contain information about ocular activity. This shows that both sensory pathways are connected at a basic level,” emphasizes Groh.
The neuroscientist hopes that her work will shed some light on how the brain coordinates these abilities and that it will also serve to better understand some ear ailments or to develop better hearing aids.
Image: Jessi Cruger – David Murphy / Duke University
Reference: The Eardrums Move When the Eyes Move: A Multisensory Effect on the Mechanics of Hearing . KG Gruters, DLK Murphy, Cole D. Jensen, DW Smith, CA Shera, and JM Groh. Proceedings of the National Academy of Sciences . January 2018. DOI: 10.1073 / pnas.1717948115
