Oculomotor Influence on the Mechanics of Hearing: Eye Movement-Related Eardrum Oscillations and Their Potential Role in Audio-Visual Spatial Integration
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After every eye movement, the brain must realign the visual and auditory reference frames in order to co-locate sights and sounds. Exactly where, when, and how such visual-auditory spatial integrations occur is not fully understood. We recently discovered that the eardrum oscillates beginning a few milliseconds before saccades and continuing until well into ensuing periods of fixation (Gruters et al., 2018)(Gruters, Murphy et al PNAS 2018). Information about at least the horizontal direction and length of saccades appear to be reflected in the phase and magnitude of these eye movement-related eardrum oscillations (EMREO).
Here, we sought to assess the full spatial characteristics of this signal for saccade parameters in both vertical and horizontal dimensions. Concurrently we sought to validate that independent estimations of vertical and horizontal saccade parameter contributions can be linearly combined to predict EMREO waveforms for saccades in all directions – a fundamental assumption of current analyses.
We found that EMREOs depend on both horizontal and vertical saccade components, varying predominantly with eye displacement, but modulated by absolute (initial or final) position as well. In toto, EMREO appear to represent combinations of these saccade parameters such that any saccade corresponds to a specific eardrum oscillation that contains a linear combination of the vertical and horizontal saccade parameters. Regressions in both the time and frequency domain create a fuller picture of the spatial information contained in EMREO. These results demonstrate that detailed information about the relationship between visual and auditory reference frames is present in the earliest stage of the auditory pathway. They also demonstrate that this information is mapped linearly and can therefore be recovered with a small set of basis components.
Future work delving into the relationship between EMREO and the transduction of incoming sounds will be needed to ascertain their effects on the processing of auditory spatial locations in relation to the visual scene. While the frequency and magnitude of EMREO suggest that they may be related to middle ear muscle contractions, the underlying mechanisms that generate them are unknown.
Murphy, David LK (2020). Oculomotor Influence on the Mechanics of Hearing: Eye Movement-Related Eardrum Oscillations and Their Potential Role in Audio-Visual Spatial Integration. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/22195.
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