Ronny Hannemann

Neural correlates of listening effort related factors: Influence of age and hearing impairment

In the last years, there has been a rising interest to find an objective method to estimate listening effort. Previously, we have shown that the wavelet phase synchronization stability (WPSS), gained from the instantaneous phase of auditory late responses (ALRs), could serve as a feasible measure for listening effort related factors. In the current study, we examined if the WPSS reflects the listening effort in young as well as middle-aged subjects and in persons with a different degree of hearing loss. To evoke ALR sequences, we generated syllabic paradigms with a different level of difficulty to evoke ALR sequences. We expected, due to the varying task demand, that the subjects require a measurable difference in the amount of effort to solve the paradigms. Additionally, a possible age and/or hearing loss related effect on the neural correlates of listening effort was investigated. The results indicate, that WPSS reflects the listening effort related factors needed to solve an auditory task. A further finding was that the reaction time data and the N1 wave amplitude information hardly yield any correlate of the invested listening effort. In addition, we noticed an age as well as hearing sensitivity related effect on the listening effort.

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 individuals 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.

Support of a patient-specific therapeutical acoustic stimulation in tinnitus by numerical modeling

The pathogenesis of tinnitus involves multiple hierarchical levels of auditory processing and appraisal of sensory saliency. Early tinnitus onset is most likely attributed to homeostatic plasticity in the periphery, while the chronification and decompensation are tightly linked to brain areas for the allocation of attentional resources, such as e.g., the thalamocortical feedback loops and the limbic system. Increased spontaneous firing after sensory deafferentation might be sufficient to generate a phantom perception, yet the question why not every peripheral hearing loss automatically elicits a tinnitus sensation is still to be addressed. Utilizing quantitative modeling of multiple hierarchical levels in the auditory pathway, we demonstrate the effects of lateral inhibition on increased spontaneous firing and the resulting elevation of firing regularity and synchronization of neural activity. The presented therapeutical approach is based on the idea of disrupting the heightened regularity of the neural population response in the tinnitus frequency range. This neural activity regularity depends on lateral dispersion of common noise and thus is susceptible for edge effects and might be influenced by a change in neural activity in bordering frequency ranges by fitted acoustical stimulation. We propose the use of patient specifically adapted tailor-made notched acoustic stimulation, utilizing modeling results for the optimal adjustment of the stimulation frequencies to archive a therapeutical edge-effect.

Neurodynamic evaluation of hearing aid features using EEG correlates of listening effort

In this study, we propose a novel estimate of listening effort using electroencephalographic data. This method is a translation of our past findings, gained from the evoked electroencephalographic activity, to the oscillatory EEG activity. To test this technique, electroencephalographic data from experienced hearing aid users with moderate hearing loss were recorded, wearing hearing aids. The investigated 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, and a setting using omnidirectional microphones without any noise reduction. The results suggest that the electroencephalographic estimate of listening effort seems to be a useful tool to map the exerted effort of the participants. In addition, the results indicate that a directional processing mode can reduce the listening effort in multitalker listening situations.

Quantification of listening effort correlates in the oscillatory EEG activity: A feasibility study

So far, a generally accepted objective measure for the listening effort estimation in clinical settings is not existent. Such a measure could support the hearing aid fitting in order to reduce the listening effort in hearing impaired patients by an adequate adaption of their personal hearing aids. In the current study, we propose a new measure for the quantification of large-scale listening effort correlates. This measure takes the phase information of the ongoing oscillatory EEG activity into account. The phase was gained from the 32 channel EEG. Then, the entropy of the extracted phase was calculated. We assume that this angular entropy reflects phase synchronization effects of the ongoing activities due to an increased attention on the relevant (speech) signal. Thus, we expect that smaller values of the angular entropy reflect a more ”ordered” process of the phase distribution. The new method was tested in 13 young normal hearing subjects using different auditory tasks consisting of differently adapted sentences to create different listening conditions. The results indicate that the angular entropy can be applied to reveal significantly differences between the solving and the relaxing part of the paradigm, i.e. between a more effortful and a more relaxing listening situation. It is concluded, that the further research includes the development of more effortful listening tasks in order to reveal also differences between the auditory paradigms.

Notched Environmental Sounds: A New Hearing Aid Supported Tinnitus Treatment Evaluated in 20 Patients.

There is converging evidence that the genesis of tinnitus is related to deterioration of inhibition and/or upregulation of gain for deprived frequency bands in the afferent auditory pathway including the auditory cortex. There is also evidence that the organisation of the auditory scene may benefit from spectral edges because of such inhibitory mechanisms. Using such spectral edges in terms of notch filtering, tailor-made notchedmusic training (TMNMT) has been suggested to reduce tinnitus loudness and tinnitusrelated auditory cortex activity and positively evaluated using subjective and objective criteria subsequently. The TMNMT is designed for patients with tonal tinnitus. They have to listen to enjoyablemusic which has a notch centred at their tinnitus frequency. It was proposed that the acoustic stimulation provided by joyfulmusic plays an important role in the reversion of the maladaptive reorganisation processes induced by the deprived frequency bands. However, apart from possibly limbically trigged reorganisation processes, a key concept of this promising TMNMT might be the suppression of the neural hyperactivity in deprived frequency bands by lateral inhibition using the notch-induced sharp spectral edge. In other words, a localised damage in the lower auditory system results – due to the tonotopic organisation of hearing path – in the bandspecific neural hyperactivity mentioned before. The tailormade notch is adjusted to the tinnitus frequency and deprived frequency band, respectively, so that the spectral edges of the deprived frequency band are enhanced. In this way, the hyperactivity within the band is suppressed by lateral inhibition. The success of this approach depends of course on the careful determination of the tinnitus sound using subjective matching procedures. Up to now, the exact range of the asymmetric lateral inhibition in human is unknown, reducing the theoretical framework of this approach to tonal, small band tinnitus sounds.

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.

Objective extraction of dynamical listening effort profiles

In complex listening environments, people with hearing loss have an increased listening effort to achieve a similar speech understanding level as normal hearing people. However, a standardized method to estimate this listening effort does not exist. Recently, we have shown a possible way to determine listening effort objectively. This method is based on the phase distribution of the ongoing oscillatory EEG activity. The aim of the current study was to assess, whether such objective methods can also be used to extract dynamical listening effort profiles in persons with a moderate hearing loss. Hearing aids were fitted using a directional microphone (DM) configuration, a new binaurally coupled hearing aid technique (BHA) and a fitting using omnidirectional microphones (ODM). Furthermore, a temporal resolution of the measure was obtained to unveil underlying processes such as fatigue effects or a cessation to spend attentional effort. The results indicate that time-varying listening effort profiles related to effects like fatigue or a cessation to solve the auditory task can be detected by the proposed objective measures.

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.

Impact of monaural frequency compression on binaural fusion at the brainstem level.

A classical objective measure for binaural fusion at the brainstem level is the so-called β-wave of the binaural interaction component (BIC) in the auditory brainstem response (ABR). However, in some cases it appeared that a reliable detection of this component still remains a challenge. In this study, we investigate the wavelet phase synchronization stability (WPSS) of ABR data for the analysis of binaural fusion and compare it to the BIC. In particular, we examine the impact of monaural nonlinear frequency compression on binaural fusion. As the auditory system is tonotopically organized, an interaural frequency mismatch caused by monaural frequency compression could negatively effect binaural fusion. In this study, only few subjects showed a detectable β-wave and in most cases only for low ITDs. However, we present a novel objective measure for binaural fusion that outperforms the current state-of-the-art technique (BIC): the WPSS analysis showed a significant difference between the phase stability of the sum of the monaurally evoked responses and the phase stability of the binaurally evoked ABR. This difference could be an indicator for binaural fusion in the brainstem. Furthermore, we observed that monaural frequency compression could indeed effect binaural fusion, as the WPSS results for this condition vary strongly from the results obtained without frequency compression.