The Concurrent OLSA Test: A Method for Speech Recognition in Multi-talker Situations at Fixed SNR.

A multi-talker paradigm is introduced that uses different attentional processes to adjust speech-recognition scores with the goal of conducting measurements at high signal-to-noise ratios (SNR). The basic idea is to simulate a group conversation with three talkers. Talkers alternately speak sentences of the German matrix test OLSA. Each time a sentence begins with the name "Kerstin" (call sign), the participant is addressed and instructed to repeat the last words of all sentences from that talker, until another talker begins a sentence with "Kerstin". The alternation of the talkers is implemented with an adjustable overlap time that causes an overlap between the call sign "Kerstin" and the target words to be repeated. Thus, the two tasks of detecting "Kerstin" and repeating target words are to be done at the same time. The paradigm was tested with 22 young normal-hearing participants (YNH) for three overlap times (0.6 s, 0.8 s, 1.0 s). Results for these overlap times show significant differences, with median target word recognition scores of 88%, 82%, and 77%, respectively (including call-sign and dual-task effects). A comparison of the dual task with the corresponding single tasks suggests that the observed effects reflect an increased cognitive load.

Binaural Signal Processing in Hearing Aids.

For many years, clinicians have understood the advantages of listening with two ears compared with one. In addition to improved speech intelligibility in quiet, noisy, and reverberant environments, binaural versus monaural listening improves perceived sound quality and decreases the effort listeners must expend to understand a target voice of interest or to monitor a multitude of potential target voices. For most individuals with bilateral hearing impairment, the body of evidence collected across decades of research has also found that the provision of two compared with one hearing aid yields significant benefit for the user. This article briefly summarizes the major advantages of binaural compared with monaural hearing, followed by a detailed description of the related technological advances in modern hearing aids. Aspects related to the communication and exchange of data between the left and right hearing aids are discussed together with typical algorithmic approaches implemented in modern hearing aids.

Effect of Directional Microphone Technology in Hearing Aids on Neural Correlates of Listening and Memory Effort: An Electroencephalographic Study.

The aim of the study was to compare the effect of different spatial noise-processing algorithms in hearing aids on listening effort and memory effort on a subjective, behavioral, and neurophysiological level using electroencephalography (EEG). Two types of directional microphone (DM) technologies for spatial noise processing were chosen: one with a wide directionality (wide DM) and another with a narrower directionality (narrow DM) to accentuate the speech source. Participants with a severe hearing loss were fitted with hearing aids and participated in two EEG experiments. In the first one, participants listened to sentences in cafeteria noise and were asked to rate the experienced listening effort. The second EEG experiment was a listening span task during which participants had to repeat sentence material and then recall the final words of the last four sentences. Subjective listening effort was lower with narrow than wide DM and EEG alpha power was reduced for the narrow DM. The results of the listening span task indicated a reduction in experienced memory effort and better memory performance. During the memory retention phase, EEG alpha level for the narrow relative to the wide DM was reduced. This effect was more pronounced during linguistically difficult sentences. This study extends previous findings, as it reveals a benefit for narrow DM in terms of cognitive performance and memory effort also on a neural level, and when speech intelligibility is almost 100%. Together, this indicates that a narrow and focused DM allows for a more efficient neurocognitive processing than a wide DM.

A preliminary investigation into hearing aid fitting based on automated real-ear measurements integrated in the fitting software: test-retest reliability, matching accuracy and perceptual outcomes.

OBJECTIVE: The recent integration of automated real-ear measurements (REM) in the fitting software facilitates the hearing aid fitting process. Such a fitting strategy, TargetMatch (TM), was evaluated. Test-retest reliability and matching accuracy were quantified, and compared to a REM-based fitting with manual adjustment. Also, it was investigated whether TM leads to better perceptual outcomes compared to a FirstFit (FF) approach, using software predictions only. Design and study sample: Ten hearing impaired participants were enrolled in a counterbalanced single-blinded cross-over study comparing TM and FF. Aided audibility, speech intelligibility and real-life benefits were assessed. Repeated measurements of both TM and REMs with manual adjustment were performed. RESULTS: Compared to a REM-based fitting with manual adjustment, TM had higher test-retest reliability. Also, TM outperformed the other fitting strategies in terms of matching accuracy. Compared to a FF, improved aided audibility and real-life benefits were found. Speech intelligibility did not improve. CONCLUSIONS: Preliminary data suggest that automated REMs increase the likelihood of meeting amplification targets compared with a FF. REMs integrated in the fitting software provide additional reliability and accuracy compared to traditional REMs. Findings need to be verified in a larger and more varied sample.

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.

The performance of an automatic acoustic-based program classifier compared to hearing aid users' manual selection of listening programs.

OBJECTIVE: To compare preference for and performance of manually selected programmes to an automatic sound classifier, the Phonak AutoSense OS. DESIGN: A single blind repeated measures study. Participants were fit with Phonak Virto V90 ITE aids; preferences for different listening programmes were compared across four different sound scenarios (speech in: quiet, noise, loud noise and a car). Following a 4-week trial preferences were reassessed and the users preferred programme was compared to the automatic classifier for sound quality and hearing in noise (HINT test) using a 12 loudspeaker array. STUDY SAMPLE: Twenty-five participants with symmetrical moderate-severe sensorineural hearing loss. RESULTS: Participant preferences of manual programme for scenarios varied considerably between and within sessions. A HINT Speech Reception Threshold (SRT) advantage was observed for the automatic classifier over participant's manual selection for speech in quiet, loud noise and car noise. Sound quality ratings were similar for both manual and automatic selections. CONCLUSIONS: The use of a sound classifier is a viable alternative to manual programme selection.

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

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. N0Sπ 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).

Open Versus Closed Hearing-Aid Fittings: A Literature Review of Both Fitting Approaches.

One of the main issues in hearing-aid fittings is the abnormal perception of the user's own voice as too loud, "boomy," or "hollow." This phenomenon known as the occlusion effect be reduced by large vents in the earmolds or by open-fit hearing aids. This review provides an overview of publications related to open and closed hearing-aid fittings. First, the occlusion effect and its consequences for perception while using hearing aids are described. Then, the advantages and disadvantages of open compared with closed fittings and their impact on the fitting process are addressed. The advantages include less occlusion, improved own-voice perception and sound quality, and increased localization performance. The disadvantages associated with open-fit hearing aids include reduced benefits of directional microphones and noise reduction, as well as less compression and less available gain before feedback. The final part of this review addresses the need for new approaches to combine the advantages of open and closed hearing-aid fittings.

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.

Fitting strategies and candidature criteria for unilateral and bilateral hearing aid fittings.

In this paper, hearing aid fitting strategies are reviewed and candidature criteria for unilateral and bilateral fittings are discussed. Fitting strategies are primarily governed by the objectives of hearing aid fitting that can be set in different ways. Based on common goals, fitting strategies can be broken down into three stages: (1) basic fitting, (2) fine-tuning and (3) verification and validation. A fine-tuning concept basing on so-called meta-controllers is described and the issue of bilateral fitting strategies is discussed. In a first order approach, bilateral hearing aids can be fitted in parallel as unilateral aids, followed by bilateral fine-tuning, making sure that loudness is balanced and overall loudness is accepted. Parallel fitting of bilateral aids is more favourable than sequential fitting to avoid rejection because of a negative experience with unilateral amplification due to difficulties in disadvantageous listening situations. Candidature criteria are presented by means of a flow chart structuring the decision making process and arriving at the conclusion that bilateral fitting should be considered the normal case. If there is any doubt about the benefit of bilateral fitting, a trial with bilateral aids should be performed.