Assessment of Vestigial Auriculomotor Activity to Acoustic Stimuli Using Electrodes In and Around the Ear.

Recently, it has been demonstrated that electromyographic (EMG) activity of auricular muscles in humans, especially the postauricular muscle (PAM), depends on the spatial location of auditory stimuli. This observation has only been shown using wet electrodes placed directly on auricular muscles. To move towards a more applied, out-of-the-laboratory setting, this study aims to investigate if similar results can be obtained using electrodes placed in custom-fitted earpieces. Furthermore, with the exception of the ground electrode, only dry-contact electrodes were used to record EMG signals, which require little to no skin preparation and can therefore be applied extremely fast. In two experiments, auditory stimuli were presented to ten participants from different spatial directions. In experiment 1, stimuli were rapid onset naturalistic stimuli presented in silence, and in experiment 2, the corresponding participant's first name, presented in a "cocktail party" environment. In both experiments, ipsilateral responses were significantly larger than contralateral responses. Furthermore, machine learning models objectively decoded the direction of stimuli significantly above chance level on a single trial basis (PAM: ≈ 80%, in-ear: ≈ 69%). There were no significant differences when participants repeated the experiments after several weeks. This study provides evidence that auricular muscle responses can be recorded reliably using an almost entirely dry-contact in-ear electrode system. The location of the PAM, and the fact that in-ear electrodes can record comparable signals, would make hearing aids interesting devices to record these auricular EMG signals and potentially utilize them as control signals in the future.

Electrophysiological and behavioural processing of complex acoustic cues.

OBJECTIVES: To examine behavioural and neural processing of pitch cues in adults with normal hearing (NH) and adults with sensorineural hearing loss (SNHL). METHODS: All participants completed a test of behavioural sensitivity to pitch cues using the TFS1 test (Moore and Sek, 2009a). Cortical potentials (N1, P2 and acoustic change complex) were recorded in response to frequency shifted (deltaF) tone complexes in an 'ABA' pattern. RESULTS: The SNHL group performed more poorly than the NH group for the TFS1 test. P2 was more reflective of pitch differences between the complexes than N1. The presence of acoustic change complex in response to the TFS transitions in the ABA stimulus varied with deltaF. Acoustic change complex amplitudes were reduced for the group with SNHL compared to controls. CONCLUSION: Behavioural performance and cortical responses reflect pitch processing depending on the salience of pitch cues. SIGNIFICANCE: These data support the use of cortical potentials and behavioural sensitivity tests to measure processing of complex acoustic cues in people with hearing loss. This approach has potential for evaluation of benefit from auditory training and hearing instrument digital signal processing strategies.