Stability of eye movement-related eardrum oscillations to acoustic and gravitational/postural manipulations

Recent studies describe Eye Movement-Related Eardrum Oscillations (EMREOs), low‑frequency signals recorded in the ear canal that arise from the tympanic membrane and are triggered by saccadic eye movements. Because EMREOs are thought to arise from motor elements in the peripheral auditory system, we examined how two known modulators of these elements affect the EMREO time course. First, the activity of outer hair cells (OHCs) can be suppressed by the medial olivocochlear reflex (MOCR). If OHCs contribute to the generation of EMREOs, activation of this reflex should reduce EMREO amplitude. To test this, we compared EMREO amplitudes elicited by saccades performed in silence and in the presence of contralateral noise. Second, postural (i.e., vestibular and proprioceptive) cues linked to head orientation may influence EMREOs via oculomotor control circuits that possibly modulate middle ear muscles. To test this, we recorded EMREOs while participants made saccades with their head upright (0° azimuth) and with their head tilted 30° in either direction. Across both experiments our data reveal no significant modulation of the EMREO by these experimental manipulations. Together with other recent studies these findings advocate for a stability of the EMREO towards multiple experimental modulations. We discuss how this fuels speculations that the signal may serve as a temporal reference frame, while also being compatible with the notion that the EMREO reflects a spatial coordinate transform for combining signals across the senses.