Implementation and Long-Term Evaluation of a Hearing Aid Supported Tinnitus Treatment Using Notched Environmental Sounds.

Recent work has shown that sharp spectral edges in acoustic stimuli might have advantageous effects in the treatment of tonal tinnitus. In the course of this paper, we evaluate the long-term effects of spectrally notched hearing aids on the subjective tinnitus distress. By merging recent experimental work with a computational tinnitus model, we modified the commercially available behind-the-ear hearing aids so that a frequency band of 0.5 octaves, centered on the patient's individual tinnitus frequency, was blocked out. Those hearing aids employ a steep notch filter that filters environmental sounds to suppress the tinnitus-related changes in neural firing by lateral inhibition. The computational model reveals a renormalization of pathologically increased neural response reliability and synchrony in response to spectrally modified input. The target group, fitted with spectrally notched hearing aids, was matched with a comparable control group, fitted with standard hearing aids of the same type but without a notch filter. We analyze the subjective self-assessment by tinnitus questionnaires, and we monitor the objective distress correlates in auditory evoked response phase data. Both, subjective and objective results show a noticeable trend of a larger therapeutic benefit for notched hearing correction.

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.

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 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.

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.

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.

Effects of auditory selective attention on chirp evoked auditory steady state responses.

Auditory steady state responses (ASSRs) are frequently used to assess auditory function. Recently, the interest in effects of attention on ASSRs has increased. In this paper, we investigated for the first time possible effects of attention on AS-SRs evoked by amplitude modulated and frequency modulated chirps paradigms. Different paradigms were designed using chirps with low and high frequency content, and the stimulation was presented in a monaural and dichotic modality. A total of 10 young subjects participated in the study, they were instructed to ignore the stimuli and after a second repetition they had to detect a deviant stimulus. In the time domain analysis, we found enhanced amplitudes for the attended conditions. Furthermore, we noticed higher amplitudes values for the condition using frequency modulated low frequency chirps evoked by a monaural stimulation. The most difference between attended and unattended modality was exhibited at the dichotic case of the amplitude modulated condition using chirps with low frequency content.

Simulations of hearing loss and hearing aid: effects on electrophysiological correlates of listening effort.

In the last decades, many investigations were done to examine the effects of sensorineural hearing loss on the speech perception ability. Besides testing hearing impaired persons, there is also the possibility to simulate the hearing loss. Therefore, some electrophysiological as well as speech recognition studies were performed in normal hearing subjects using techniques to model the sensorineural hearing loss. Thus, the effects of peripheral hearing loss without central auditory pathologies can be examined. In previous studies, we have shown, that the wavelet phase synchronization stability (WPSS) of auditory late responses could serve as a possible indicator of listening effort. Now, the aims of this present study were to explore the effects on the WPSS by using two different simulations of hearing loss and a simulated hearing aid. The preliminary results showed, that in case of a simultaneous simulation of hearing loss by noise masking and a hearing aid, an objective discrimination between an easy and a difficult listening situation can be achieved. Furthermore, the WPSS reflected also a good discrimination by using the filtered and attenuated paradigms.

The effects of age and hearing impairment on the extraction of listening effort correlates.

In clinical practice, an objective method to assess listening effort is still not available. The benefit of such a measure would be to reduce the listening effort in hearing impaired persons by an adequate adaption of their personal hearing aids. In foregoing studies, we have shown that the wavelet phase synchronization stability (WPSS) of auditory late responses (ALRs) could serve as a feasible measure of listening effort. Here, tonal and noise embedded syllabic paradigms were employed to achieve ALR sequences in normal hearing subjects. The aims of this ongoing study were 1) to extract the WPSS of ALR sequences in hearing impaired persons, middle-aged normal hearing persons and younger normal hearing subjects, 2) to investigate possible age-related influences on the WPSS and 3) to examine a feasible influence of the hearing loss on the WPSS. It is concluded, that the WPSS of ALR sequences can be extracted in normal hearing as well as in hearing impaired persons. An age related effect regarding the WPSS was not noticeable and the intergroup comparison of the difference of the WPSS showed a tendency to be larger for the hearing impaired compared to the normal hearing middle-aged subjects. The latest can be interpreted that this subject group showed a larger effort to solve the auditory paradigms.

Auditory streaming and listening effort: an event related potential study.

Until now, an objective method to estimate listening effort with a minimum level of cooperation of the patient in order to fit hearing aids is not existent. The benefit of such a method would be to reduce the listening effort in hearing impaired persons by an adequate adaption of the hearing aids. Recently, we have shown that the wavelet phase synchronization stability (WPSS) of auditory late responses could serve as a measure to estimate listening effort. In this paper, we extend our previous studies by using for the first time syllable stimulation paradigms with two levels of difficulty due to the combination of the syllables. Furthermore, by taking the model of auditory stream selection into account, the complexity of the paradigms was enhanced by the generation of a second competing auditory stream beside the syllable stream. This stream consisted of multitalker babble noise at two different signal to noise ratios in order to mimic noisy environments. The data was collected from a total of 21 normal hearing subjects, who had always to detect a target syllable. It is concluded, that the WPSS is a robust measure to perceive differences between the effort needed to solve a task in an easy and a difficult listening condition. However, a further research will be to test hearing impaired persons to prove, if this electrophysiological method could be applied to improve the hearing aid fitting procedures in clinical settings.

Non-listening effort related parameters in auditory discrimination paradigms.

Objective methods to asses listening effort are still missing in clinical settings. Thus, the focus of our ongoing research is the extraction of possible substrates of listening effort. This paper focuses on the non-effort related factor reaction time (RT) on the different components of auditory late responses (ALRs). It makes sense to consider this factor in the context of age related changes of the RT. For the comparison of the ALR components and the RT, two syllable oddball paradigms with different degree of difficulty were created. The paradigms were embedded in multitalker babble noise to create a realistic listening situation. The data was collected from 13 normal hearing healthy subjects, who had to detect a deviant. Furthermore, the wavelet phase synchronization stability (WPSS) was calculated for different scales. A filter bank was designed in order to separate the components by their frequency content. Finally, the Pearson product-moment correlation coefficient was calculated to clarify if there is a possible linkage between the RT and the ALR components. The results show, that only the P(3) latency is correlated with the RT. A relation between the RT and the other ALR components could not be observed. It is concluded, that the focus of our further research, will be on the N(1) and the P(2) wave due to the fact that those components are independent from the non- effort related factor reaction time.

Electrophysiological correlates of listening effort: neurodynamical modeling and measurement.

An increased listing effort represents a major problem in humans with hearing impairment. Neurodiagnostic methods for an objective listening effort estimation might support hearing instrument fitting procedures. However the cognitive neurodynamics of listening effort is far from being understood and its neural correlates have not been identified yet. In this paper we analyze the cognitive neurodynamics of listening effort by using methods of forward neurophysical modeling and time-scale electroencephalographic neurodiagnostics. In particular, we present a forward neurophysical model for auditory late responses (ALRs) as large-scale listening effort correlates. Here endogenously driven top-down projections related to listening effort are mapped to corticothalamic feedback pathways which were analyzed for the selective attention neurodynamics before. We show that this model represents well the time-scale phase stability analysis of experimental electroencephalographic data from auditory discrimination paradigms. It is concluded that the proposed neurophysical and neuropsychological framework is appropriate for the analysis of listening effort and might help to develop objective electroencephalographic methods for its estimation in future.

On the cognitive neurodynamics of listening effort: a phase clustering analysis of large-scale neural correlates.

An increased listening effort represents a major problem in humans with hearing impairment. Neurodiagnostic methods for an objective listening effort estimation could revolutionize auditory rehabilitation. However the cognitive neurodynamics of listening effort is not understood and research related its neural correlates is still in its infancy. In this paper we present a phase clustering analysis of large-scale listening effort correlates in auditory late responses (ALRs). For this we apply the complex wavelet transform as well as tight Gabor Frame (TGF) operators. We show (a) that phase clustering on the unit circle can separate ALR data from auditory paradigms which require a graduated effort for their solution; (b) the application of TGFs for an inverse artificial phase stabilization at the alpha/theta-border enlarges the endogenously driven listening effort correlates in the reconstructed time- domain waveforms. It is concluded that listening effort correlates can be extracted from ALR sequences using an instantaneous phase clustering analysis, at least by means of the applied experimental pure tone paradigm.