Matthias Latzel

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.

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.

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 α/θ-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.

Speech reception with different bilateral directional processing schemes: Influence of binaural hearing, audiometric asymmetry, and acoustic scenario

ABSTRACT Hearing aid (HA) users can differ markedly in their benefit from directional processing (or beamforming) algorithms. The current study therefore investigated candidacy for different bilateral directional processing schemes. Groups of elderly listeners with symmetric (N = 20) or asymmetric (N = 19) hearing thresholds for frequencies below 2 kHz, a large spread in the binaural intelligibility level difference (BILD), and no difference in age, overall degree of hearing loss, or performance on a measure of selective attention took part. Aided speech reception was measured using virtual acoustics together with a simulation of a linked pair of completely occluding behind‐the‐ear HAs. Five processing schemes and three acoustic scenarios were used. The processing schemes differed in the tradeoff between signal‐to‐noise ratio (SNR) improvement and binaural cue preservation. The acoustic scenarios consisted of a frontal target talker presented against two speech maskers from ±60° azimuth or spatially diffuse cafeteria noise. For both groups, a significant interaction between BILD, processing scheme, and acoustic scenario was found. This interaction implied that, in situations with lateral speech maskers, HA users with BILDs larger than about 2 dB profited more from preserved low‐frequency binaural cues than from greater SNR improvement, whereas for smaller BILDs the opposite was true. Audiometric asymmetry reduced the influence of binaural hearing. In spatially diffuse noise, the maximal SNR improvement was generally beneficial. N0S&pgr; detection performance at 500 Hz predicted the benefit from low‐frequency binaural cues. Together, these findings provide a basis for adapting bilateral directional processing to individual and situational influences. Further research is needed to investigate their generalizability to more realistic HA conditions (e.g., with low‐frequency vent‐transmitted sound). HIGHLIGHTSBinaural hearing, audiometric asymmetry, and acoustic scenario influence speech reception with bilateral directional processing.For lateral speech maskers, binaural hearing modulates benefit from preserved low‐frequency binaural cues.For spatially diffuse noise, maximal signal‐to‐noise ratio improvement is beneficial.Audiometric asymmetry <2 kHz reduces the influence of binaural hearing.N0S&pgr; detection at 500 Hz predicts benefit from low‐frequency binaural cues.

On the objective electrophysiological estimation of listening effort in different age groups

The basic approaches to fit hearing aids were commonly based on findings of how young persons hear sounds in ideal conditions. In order to improve hearing aid fitting methods, the focus of the new approaches should be based on auditory processing and cognition information of older adults. In previous studies with young subjects, employing tonebursts and in noise embedded syllabic paradigms, we have shown that the Wavelet Phase Synchronization Stability (WPSS) of Auditory Late Responses (ALRs) can serve as an objective indicator of listening effort. The purpose of this preliminary work, which precedes a study with hearing impaired persons, is to examine possible age-related differences in the WPSS and ALRs by testing syllabic paradigms in two different age groups and using two different levels of task complexity. The WPSS discriminated between difficult and easy test conditions, which is in line with our previous findings. The latest was consistent in both age groups. Age-related differences regarding the WPSS could not be observed.

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 P3 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 N1 and the P2 wave due to the fact that those components are independent from the non- effort related factor reaction time.

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.

Effect of Hearing Aid Directionality and Remote Microphone on Speech Intelligibility in Complex Listening Situations

Remote microphones (RMs) have been developed to support hearing aid (HA) users in understanding distant talkers. In traditional clinical applications, a drawback of these systems is the deteriorated speech intelligibility in the near field. This study investigates advantages and disadvantages of clinical RM usage and the effects of different directionality settings of the HAs in complex listening situations in the laboratory. Speech intelligibility was investigated in 15 experienced severely hearing impaired participants in a noisy environment using a dual-task test paradigm where the tasks were presented from either a near field or a far field loudspeaker. Primary and secondary tasks were presented simultaneously so attention had to be shared on both tasks. In a second experiment, two speech intelligibility tests were presented from either the near field or the far field loudspeaker. The tests were interleaved to simulate a complex listening situation with shifting attention. Directional HA microphones yielded better performance than omnidirectional microphones (both combined with a RM) in near field when analyzing both tasks of the dual-task experiment separately. Furthermore, the integrated dual-task test results showed better performance with directional HA microphones compared with the omnidirectional setting (both cases in combination with a RM). These findings were confirmed by the results of the interleaved speech intelligibility test.

Syllable evoked auditory late responses: Effects of noise onsets and noise types

Listening in noisy situations demands cognitive effort. Recently, we have shown that the Wavelet Phase Synchronization Stability (WPSS) of Auditory Late Responses (ALRs) represents an objective method to estimate mental load in auditory environments. In literature only a limited number of publications can be found which focus on the effects of noise types and noise onset effects using syllable evoked ALRs. The objective of the present work was to analyze the influence of different parameters, like white and babble noise as well as different noise onset times 50, 300, 1000ms and continuous noise conditions, on syllable evoked ALRs. Also, the analysis of the WPSS, as used in previous work, has never been applied to see such effects on the ALRs. We found that noise onset times of 300ms or larger showed a good separation of the ALR components. Furthermore, the analysis of the WPSS for different scales showed a clear identification of the N1 components. However, the best type of noise, and noise onset configuration depends on the specific application. For investigations related to auditory processing of speech, ecological noises are preferred because they could be used to mimic everyday listening situations.