157 — The eardrums move when the eyes move: A multisensory effect on the mechanics of hearing

It’s well established that visual information under scrutiny by primate brains affects the auditory processing of the same cues: Changing what a primate sees can change what he or she hears. In general, it’s believed that this adjustment takes place in the brain.

But this paper demonstrates that middle ear muscles — the stapedius and tensor tympani — adjust the position and orientation of the eardrum itself in response to the motion of the eyes. These motions, dubbed “eye-movement-related eardrum oscillations” or EMREOs, are detected by placing a small, hyper-sensitive microphones in the ear canal and listening for the quiet vibrations that indicate a movement of this miniscule musculature.

The authors found that even in the absence of sounds, the eardrum musculature was manipulated. And when this was compared to eye motion (saccades), it became clear that these motions corresponded directly to the motions of the eyes. (The researchesr were able to establish this by measuring the positions of the eyes of monkeys and humans in response to click stimuli or light stimuli.)

These motions are really interesting because it means that there is a relationship between the auditory and visual systems prior to cortex: Somehow, information is journeying from sensory cortex back out to the sensory organs themselves.

I imagine that these feedback systems enable higher-fidelity spatial acuity when trying to locate the origin of a stimulus in 3D space. But this immensely complicated system is fascinating: I wonder when in the evolutionary chain this began to arise.