Unraveling eye movement-related eardrum oscillations (EMREOs): how saccade direction and middle ear properties shape amplitude and time course

Abstract

Eye movement-related eardrum oscillations (EMREOs) reflect movements of the tympanic membrane that are known to scale with the magnitude and direction of saccades. While EMREOs have been consistently described in humans and non-human primates, many questions regarding this phenomenon remain open. Based on bilateral in-ear recordings in human participants we here probe a number of their properties that improve our understanding of the EMREOs' origin and functional significance. We show that the time courses are comparable between the left and right ears, and between paradigms guiding saccades by visual and auditory targets. However, the precise time course and amplitude differ significantly between ipsi- and contralateral saccades beyond the previously known phase-inversion described for saccades in opposing directions. Finally, we show that the EMREO amplitude is negatively related to the compliance of the tympanic membrane. These results altogether raise potential challenges for the interpretation of EMREOs in the light of a coordinate-alignment between vision and hearing. Furthermore, they support the notion that EMREOs largely reflect motor-related top-down signals that are relayed to the middle ear muscles in a differential principle similar as governing the execution of ipsi- and contralateral saccades.