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.

Speech induced binaural beats: Electrophysiological assessment of binaural interaction.

This paper introduces and evaluates a speech signal manipulation scheme that generates transient speech induced binaural beats (SBBs). These SBBs can only be perceived when different signals are presented dichotically (to both ears). Event-related potentials were recorded in 22 normal-hearing subjects. Dichotic stimulus presentation reliably evoked auditory late responses (ALRs) in all subjects using such manipulated signals. As control measurements, diotic stimulation modalities were presented to confirm that the ALRs were not evoked by the speech signal itself or that the signal manipulation scheme created audible artifacts. Since diotic measurements evoked no ALRs, responses from dichotic stimulation are a pure correlate of binaural interaction. While there are several auditory stimuli (mostly modulated sinusoids or noise) that share this characteristic, none of them are based on running speech. Because SBBs can be added to any arbitrary speech signal, they could easily be combined with psychoacoustic tests, for example speech reception thresholds, adding an objective measure of binaural interaction.

Objective assessment of listening effort: effects of an increased task demand.

In demanding listening situations the individual has to exert an increased listening effort to process interesting auditory signals correctly. Especially people with hearing loss are particularly affected and require more effort to identify sounds compared to those with normal hearing. So far, a suitable objective estimate of listening effort is still not available. In previous studies, we presented an objective estimate of listening effort (OLEosc), which is based on the instantaneous phase distribution of the ongoing EEG activity. In the current study, the proposed measure was analyzed in detail. The task performance was taken into account, which indicates if the participants can solve the auditory task and exert effort or if they ceased solving the task. The EEG data was acquired from people with moderate hearing loss solving a listening task. During the experiment, hearing aid settings with different microphone configurations were tested. The results indicate that the OLEosc reflects the real exerted effort of the participants. Besides the reflection of different task demands related to the hearing aid settings, it was possible to show a decline of focused attention to the auditory stimuli related to an excessive task demand. Furthermore, the data indicate that the OLEosc is not directly correlated to the speech intelligibility presented in the word score data and is not subjectively biased like the results of the presented rating scale.

Towards the assessment of listening effort in real life situations: Mobile EEG recordings in a multimodal driving situation.

The EEG estimation of listening effort has been proven to efficiently map subjectively perceived effort on an objective scale. However, it has mostly been performed in controlled audiometric laboratory environments. In this study, we investigated the feasibility of the EEG listening effort assessment in a multisensory demanding environment. For this purpose, two mobile EEG acquisition systems were used to extract the objective listening effort of the ongoing oscillatory activity (OLEosc) while driving. As an auditory paradigm was presented to trigger listening effort, the simulated driving scenario served as a competing task responding to different modalities. The OLEosc was compared with a subjective rating of the expended listening effort and the task performance. Furthermore, we considered time resolved listening effort profiles over the duration of the paradigm. The results showed that the practical assessment of listening effort in a multimodal real life setting is viable. The OLEosc could be extracted and followed the subjective listening effort. Moreover, the analysis of the dynamic listening effort profiles unveiled further information such as "surrender effects", when the subjects ceased to solve the auditory task due to the intense multimodal load.

Objective assessment of listening effort in the oscillatory EEG: comparison of different hearing aid configurations.

An objective estimate of listening effort could support the hearing aid fitting procedure. Most of the digital hearing aids have already hearing aid settings which are supposed to reduce the listening effort, but the effects of these settings on the individual's listening effort remain unclear. In this study, we propose an objective estimate of listening effort using electroencephalographic data. The new method is based on the phase distribution of the ongoing oscillatory EEG activity. We hypothesize that for a non-effortful listening environment the phase is rather uniformly distributed on the unit circle than for a demanding condition. To prove if the phase is uniformly distributed around the unit circle, the Rayleigh Test was applied to the phase of the EEG. This method was tested in 14 hearing impaired subjects (moderate hearing loss, 65.64 ±7.93 yrs, 7 female). The tested hearing aid settings were a directional microphone combined with a noise reduction algorithm in a medium and a strong setting, the noise reduction setting turned off as well as a setting using omnidirectional microphones. Noise embedded sentences (Oldenburg Sentence Test, OlSa) were used as test materials. The task of the subject was to repeat each sentence. The results indicate that the objective estimate of listening effort maps the subjectively rated effort and for a listening situation like the presented one, the strong setting of the directional microphone requires the smallest effort.

Assessment of post-excitatory long-interval cortical inhibition in adult attention-deficit/hyperactivity disorder.

In order to further examine cortical impairment in adult ADHD patients and to test the hypothesis of a disturbed neuronal inhibition in adults with ADHD, late auditory evoked potentials were measured. By using paired-chirp auditory late responses, we compared 15 adults with ADHD with 15 control subjects, focusing on the inhibition elicited by the stimuli. Besides amplitude measurements, a time-frequency phase coherence study using the wavelet phase synchronization stability (WPSS) was performed. ADHD was diagnosed according to DSM-IV criteria. All ADHD subjects were without medication and did not suffer from any further axis I disorder. WPSS analysis revealed impaired auditory inhibition for ADHD patients for interstimulus intervals (ISI) between 500 and 1,100 ms as compared with healthy controls. By analyzing the WPSS in the interval from 80 ms to 220 ms, mean inhibition of the test chirp was found to be 6% in the ADHD group and 38.5% in the control subjects (p = 0.01). Moreover, overall smaller amplitudes in the N100 and P200 waves at all ISI were found (p = 0.04 and p = 0.02). However, reproducibility indices in the amplitude measurements were low, thus supporting the use of the instantaneous phase-based analysis method. The results support the hypothesis of reduced intracortical inhibition as a correlate of disturbed brain function in adults with ADHD.

Assessment of aversive stimuli dependent attentional binding by the N170 VEP component.

For social species nonverbal communication by assessment of emotion expression is crucial for building up and maintaining social structures. In humans, body language not only includes gestures but also a variety of facial expressions. Negative associated facial expressions, e.g. disgust, fear, anger call for a higher attentional binding due their evolutionary background, denoting directly personal dangers for the receptive individual. In a number of psychiatric disorders such as schizophrenia or autism spectrum diseases, the assessment of emotions in faces is disturbed, leading to even more pronounced social cuts. In this article we present a new methodology for monitoring the attentional binding to emotion-tinged stimuli in a face recognition task. We were able to demonstrate a significant difference in habituation behavior to neutral and negative associated faces respectively. In future, this methodology might provide a fast and reliable scheme for the detection of psychiatric disorders comprising dysfunction of limbic structures.