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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 23  |  Issue : 1  |  Page : 21-26

Influence of channel and ChannelFree™ processing technology on the vocal parameters in hearing-impaired individuals


1 Department of Speech and Hearing, Nitte Institute of Speech and Hearing Medical Science Complex, Mangalore, India
2 Department of Speech and Hearing, School of Allied Health Sciences, Manipal University, Manipal, Karnataka, India

Date of Web Publication6-Feb-2017

Correspondence Address:
Gopika Kizhakke Kodiyath
Department of Speech and Hearing, School of Allied Health Sciences, Manipal University, Manipal - 576 104, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-7749.199506

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  Abstract 

Introduction: Hearing loss is common in all age ranged population. Hearing loss leads to poor speech perception in quiet and more in noisy situation. Intact system over comes problem by masking release ability and its mechanism however impaired system fails to do. Hearing aid being common rehabilitation option, strategies and technology tries to support better speech perception in noise. Hence comparative studies of technology and strategies for the betterment of impaired population are needed. Objective of the Study: Enhancing speech perception is being the mainstay of hearing aid manufactures, Comparison of ChannelFreeTM, novel technology which claiming superior speech perception with channel hearing aids, specifically for competing signals is the objective. Materials and Methods: Thirty-three clients fitted with multi-channel and ChannelFreeTM with noise reductions (NR) On, Off condition. Comodulated and Uncomodulated masking release was the outcome measure in free field condition through audiometer. Results: Overall, ChannelFreeTM performed superior over channel hearing aids. Effect of channels, NR, and modulation type of background noise played key role. Perceptually, ChannelFreeTM was significantly preferred, especially in the first time users. Conclusion: ChannelFreeTM hearing aid strategies and NR are able to process incoming signal faster in order to retain the spectral contrast and also facilitate temporal cues from the amplified speech in noise. Acclimatization period has a vital role. Updating and implementing the validated novel technologies for the hearing impaired individual is recommended.

Keywords: ChannelFree™ hearing aids, cochlear hearing loss, comodulation masking release, multichannel hearing aids


How to cite this article:
Kodiyath GK, Mohan KM, Bellur R. Influence of channel and ChannelFree™ processing technology on the vocal parameters in hearing-impaired individuals. Indian J Otol 2017;23:21-6

How to cite this URL:
Kodiyath GK, Mohan KM, Bellur R. Influence of channel and ChannelFree™ processing technology on the vocal parameters in hearing-impaired individuals. Indian J Otol [serial online] 2017 [cited 2020 Feb 23];23:21-6. Available from: http://www.indianjotol.org/text.asp?2017/23/1/21/199506


  Introduction Top


Speech is a complex signal which has multiple temporal characteristics [1] because it encompasses the quickly changing elements that require for the representation of temporal information, mainly in competing signal condition. Temporal processing abilities help in perceiving the signal which changes over time.

Identifying and understanding speech, especially in the presence of competitive signal really troublesome for individuals with hearing impairment, especially people with sensorineural hearing losses [2],[3] because most of the speech segments are either not audible or the speech signals itself get distorted for them.[4] Detecting and analyzing energy at one frequency in the presence of energy at the other frequencies is markedly affected in sensorineural impairment.[5] Along with this, detecting rapidly changing signal that rapidly follows or rapidly followed by a different signal also difficult for them.[5] This decreased frequency resolution and temporal resolution make it more likely that noise will mask speech than would be the case for a normal hearing person. This is mainly because of the widening of auditory filters in cochlear hearing loss individuals. This will leads to great need for larger signal to noise ratio (3–6 dB) than normal in order to communicate effectively, even when sounds have been amplified by a hearing aid.[5]

Temporal cues in incoming signals are the center for speech perception [6] in such competing signal conditions. The contributions of temporal envelope (E) coherence between critical bands [7] and temporal fine structure (TFS) cues [3],[8] of the signal are very helpful to the listeners in differentiating the desired signal from noisy environment precisely. The reduced ability of hearing impaired individual to perceive speech in noise can be due to the poor TFS cues [3] in comparison with normal hearing subjects. These cues are markedly helpful when the maskers are modulated or fluctuating in their amplitude level.[3] Hence the effectiveness with the amplification devices such as cochlear implant and hearing aids will relay on listeners sensitivity with TFS cues to extract desired signal in noisy conditions.[8]

There are standardized psychophysical tests are also available to quantify temporal sensitivity usually aim to measure one's ability to identify or discriminate changes in the temporal properties of the incoming signal.[9] Detection thresholds of less complex stimuli like tones can be reduced when the masker carries coherent modulations across frequency channels.[10] This effect is known as comodulation masking release (CMR). It is the one of the important tool to measure temporal processing, as it helps to enhance the detection of the auditory signals from competing signal by the addition of energy in frequency regions well removed from the frequency of the signal. Nevertheless, it is important that added energy must be amplitude modulated in a coherent way across frequencies, i.e., co modulated.[11] There are varieties of hypothesis was set to explain the possible mechanism behind this CMR. Evidences are proposed that both within and across channel cues are important for the detection of signal in competing signal.[12] In psychophysics, CMR is well appreciated as it offers quantitative and well reliable information on listener's ability to perceive speech signal in modulated noisy situations such as multitalker and reverberant listening environments. Literature prefers to describe it as the “cocktail party problem” or “cocktail party effect,” it has been well discussed in the current reviews.[13]

Hearing aids are the primary rehabilitation option for individual with hearing loss.[14] Since the recognition of speech is the most important function of our hearing system in daily life,[15] the expectation from the hearing aids in this general living environment is also high among them.[16] In order to stamp out the barriers created by the competing signal in speech perception, plenty of technologies and strategies such as channels, bands, noise reduction (NR) and directional microphone have been implemented in hearing aids. Effective noise control measures have a positive effect on individual with hearing loss.[16]

Channels and bands in hearing aids

Among this, band is used to have a volume control in each frequency, whereas channels will split the entire frequency spectrum into different individual range of frequencies. In the present era, there are devices come up with more than 24 channels. This allows applying different strategies such as NR to differentiate noise from speech in each channel differently. Hence, greater the number of channels, more precision in the fine tuning which in turns retain “frequency resolution”[17] and “volume resolution” which will be matching the near normal audiogram by increasing the audibility.[18] In contrast to these, few studies are enlightened with the fact that beyond a certain number of channels increasing numbers of channels none of the currently used hearing aids show superior performance in speech perception.[19]

Noise reduction in hearing aids

NR algorithms implemented in hearing aids plays a crucial role in improving speech intelligibility in presence of background noise.[3],[20],[21] These strategies can be incorporated differently (adaptive or static) into the devices depends upon the manufacturer. This is done so as to identify the predominant signals and to reduce band gain for signals with dominant noise.[22] A feature known as active NR uses an algorithm, to differentiate speech from noise in each frequency channel and accordingly adapt the gain. This was possible because of the inherent differences in the modulation characteristics of the speech and noise signals.[23] The NR strategies can be applied differently based on the number of channels in the hearing aids.

ChannelFree™ hearing aids

Bernafon's ChannelFree™ signal processing, is the one of the newly implemented and widely marketed technology which claims superior performance in speech perception based on its improvement in temporal resolution, frequency resolution, and spectral contrast. This is possible by offering small analyzing window without splitting the spectrum into multiple channels and quick signal processing strategies, thereby it provides gain adjusted up to 20,000 times per se cond.[24]

ChannelFree™ hearing aids in speech perception

In speech, every sound is different from the other with respect to acoustic features. Consonants such as/t/are very softer than vowels such as/e/. Hence, hearing impaired individuals are often failed to spot very soft phonemes. Amplifications systems are required to tackle these issues. In ChannelFree™ hearing aid, by not splitting up the frequency spectrum in the incoming signal, the aid can retain spectral contrast in the signal, because the rate of signal level processing by the hearing aid is about 2000 a second.[24] These advanced features in ChannelFree™ hearing aids help it to recognize even the shortest as well as the weakest speech segments. This allows applying instantaneous and accurate gain with less distortion. Phoneme level processing in ChannelFree™ hearing aids assists in solving the problem of listening in multiple listening situations [23] by achieving maximum speech intelligibility and smooth speech quality.

Very limited studies have done on this topic.[25] The study findings reported that the ChannelFree™ hearing aids performance were well appreciated by seven out of 13 hearing impaired individuals when comparing with multichannel hearing aids, but this is not evident in objective measure. Another comparative study by [25] study in open canal hearing instruments showed no significant difference was found between behavioral and subjective results between the two signal processing strategies, but it was significantly better than unaided condition.

Moreover, these benefits are reported based on the limited research and development of company perspectives without being proved or documented scientifically on clinical population with cochlear hearing loss. Hence, there is a great need for substantiate its benefits in daily listening conditions before implementing this in a clinical setup. With both technologies currently available commercially in hearing aids, there is a need to study the differences in these signal processing strategies and their effects on temporal processing by using psychophysical test such as CMR, because it is very significant to quantify one's quality of life by measuring speech reception under competing signal conditions, especially in a cocktail party environment.[26],[27]

The aim of the present study is to compare the modulation detection function using multi three channel and ChannelFree™ technologies in individuals with hearing impaired. The objectives of the study were as follows:

  • To estimate the modulation detection functions with multi three channel and ChannelFree™ signal processing
  • To estimate the impact of NR strategies on the modulation detection
  • To analyze the interaction effect between modulation detections, NR, and signal processing
  • To compare subjective perception toward signal perception.



  Materials and Methods Top


A cross-sectional study design was carried out for this study. Entire test procedures were carried out in sound treated room by maintaining the ambient noise levels within the permissible levels. Convenient sampling was used to collect data by including 33 participants with both unilateral or bilateral sensory hearing loss (total of 49 ears) with the degree of mild, moderate and moderately severe based on detailed case history and conventional audiometric findings. Participants were excluded with middle ear pathology, neuro-otological, and cognitive deficits. Among this, both first time hearing aid users as well as experienced hearing aid users were there with the age range of 18–75 years (52.82 ± 18.15 years).

Selection and fitting of amplification devices

Both Bernafon three channel (WIN 102 or WIN 112) and Bernafon ChannelFree™ (INZIA 1) digital hearing aids were used on all selected individuals and with fitting done as NAL-NL1 prescriptive approach, keeping it with first fit level, and aided response within speech spectrum. Additional changes were also done if the patients ask for it.

NR, local controls (microphone and telecoil), and mute functions were kept on and off in each hearing aids for each trials.

Test administration

Stimuli for CMR for this study were generated with the sampling rate of 44 kHz and were converted to analog signals by a high-quality 24-bit sound card. The target signal for the experiment was 1000 Hz pure tone. On frequency masker (OFM) would be centered at 1000 Hz and flanking band maskers (FBM) would be centered at 250 Hz, 500 Hz, 2000 Hz, and 4000 Hz. Both OFM and FMs were the bandwidth of 20 Hz. The total duration of target signal and maskers were 200 ms with 20 ms cosine-squared onset/offset ramps. Similarly stimuli for un-co modulation masking release (UCMR) also used with the target signal of 1000 Hz pure tone, i.e., The FBM was pure tones amplitude modulated either in phase (CMR) or out of phase (UCMR) with the on-frequency component.

Stimuli will be presented via a laptop computer connected to audiometer in free field condition. All the CMR stimuli were presented using maximum likelihood procedure (MLP) toolbox, which implements an MLP in MATLAB (Grassi and Soranzo, 2008). Stimuli will be recorded at 44,100 Hz sampling rate. A two-interval alternate forced-choice method using an MLP will be employed to track an 80% correct response criterion to determine the threshold of the sinus tone in the masking noise bands. Therefore, out of two masking noise complexes, one of it contained the sinus tone. After presenting the stimuli, the participants were forced to choose in which of the two noise complexes the tone was. The test subject was instructed to guess the answer if he/she did not hear the tone. In order to familiarize with the test procedure, demonstration, and trial sessions were given before initiating the actual test. If required, break time is also provided. The test time taken for completing eight trials was around 45 min in each ear. All the stimuli were presented at their comfortable level, through loudspeaker in a sound treated room. If the hearing sensitivity in the contralateral ear is normal or mild hearing loss, ear plugs are used to occlude the ear in order to avoid better ear participation in their performance.[28]

Subjective performance is necessary to find the overall performance. In this test procedure, the participants were not getting sufficient time to get acclimatized with the hearing aids. Hence, five point performance rating scale was used to check the subjective speech perception with two different hearing aid technologies after exploring different listening conditions. In the rating scale, five is exceptional and one is unsatisfactory. In order to avoid the bias factors, one-way blind folding was taken for entire test procedure.


  Results Top


The yielded data was analyzed with SPSS Version 16.0 (SPSS Inc. Released 2007. SPSS for Windows, Version 16.0. Chicago, SPSS Inc.). Three-way ANOVA repeated measures with a significance level of 0.05 and Bonferroni's adjustment was used to investigate the mean effects of channel processing, NR, and modulation type of background noise on detection thresholds of tone.

The analysis revealed that there is a significant mean effects of channel processing on detection threshold (F (1, 48) = 4.937, P = 0.031). This indicates that irrespective of NR on or off and test is CMR or UCMR, channel free perform better than multi three channel hearing aids. Similarly, the effects of NR on detection threshold also was significant (F (1, 48) = 29.53, P = 0.00). This again signifies the efficacy of NR strategies in both the hearing aids in the test performance. Even the modulation type of background noise also had significant difference (F (1, 48) = 31.01, P = 0.00), irrespective of NR and types of hearing aids.

Interaction effect between signal processing and NR (F (1, 48) = 0.77, P = 0.38) revealed no significant difference. This suggest that both the hearing aids had equal or near equal performance in masking release when the NR was on and off. Similarly, no significant interaction was seen between signal processing and modulation detection (F (1, 48) = 2.53, P = 0.38). However, the interaction between NR and modulation was significant (F (1, 48) = 5.18, P = 0.027).

Since there is an interaction, follow-up planned comparison test was performed to confirm with each type of background noise. Surprisingly, there is a significant difference found (P < 0.05) in the modulation function (between CMR and UCMR) in both three channel and ChannelFree™ hearing aids when the NR was on and off. [Table 1] describes the performance of hearing aids in terms of modulation detection under CMR and UCMR condition when the NR was on and off. Similarly, hearing aid performance in modulation detection with NR on and off condition for multi three channel and ChannelFree™ conditions are graphically represented in [Figure 1].
Table I: Describing the performance of hearing aids in terms of modulation detection under CMR and UCMR condition when the NR was on and off

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Figure 1: Graphical representation of hearing aid performance in modulation detection with noise reduction on and off condition for multi three channel and ChannelFreeTM conditions. MC: Multichannel hearing aids, CF: ChannelFreeTM hearing aids, On: Noise reduction was on, Off: Noise reduction was Off, CMR: Comodulation masking release, UCMR: Uncomodulated masking release.

Click here to view


This study also compared the speech quality rating by the 15 participants using five point rating scale, after fitting each hearing aid using statistical test of significance (Wilcoxon signed rank test) at 0.05 level to document hearing aid benefit in real-world listening situations. Results indicated that subjectively the performance of ChannelFree™ hearing aids in various listening conditions showed excellent benefits than the basic hearing aids (P < 0.05).

Among these 15 participants, eight were first time hearing aid users, whereas seven participants were experienced users of three channel hearing aids. Interestingly, in this study, results showed that in the former group, all the participants reported that ChannelFree™ hearing aids are better than three channel hearing aids, in terms of speech quality [Figure 2]. But among the latter group, there was variability across the participants. Only 2 out of 7 participants rated ChannelFree™ hearing aids as a better option [Figure 3].
Figure 2: Perceptual rating (5 point rating scale) for both the hearing aids on speech quality by first time hearing aid users in different day to day life situation.

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Figure 3: Perceptual rating (5 point rating scale) for both the hearing aids on speech quality by experienced users in different day to day life situation.

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  Discussion Top


Over all, this study finding showed there is a notable improvement in ChannelFree™ hearing aids in detection thresholds. This gives a clear idea that ChannelFree™ hearing aids strategies are well capable to make TFS cues available from the amplified speech in noise signal by utilizing their residual hearing. Because ChannelFree™ hearing aids process the incoming signal so faster in order to retain the spectral contrast in the signal. Even though literature on ChannelFree™ hearing aids were focused on different aspects of signal processing, the current study finding contradicting those study findings on their performance.[25]

Both hearing aids performed well when the NR was activated. This provides a clear cut view on the necessity of NR strategies even in basic hearing aids to improve signal to noise ratio. Since the background noise is highly damaging to speech intelligibility for hearing impaired individuals.[4] NR algorithms implemented in hearing aids play an important role in improving speech intelligibility in the presence of competing signal.[20],[21] However, new advancement and novel technologies will offer additional features.

Signal detection in comodulated background noise was higher than in un-comodulated conditions in both the hearing aids. This improvement in CMR can be attributed to frequency specific gain shaping which compensates for level differences as CMR depends on level difference between on-frequency and off-frequency bands. This again supporting the earlier studies that are emerged with the conclusion of enhanced signal detection when it is embedded in a amplitude modulated maskers rather than unmodulated noise [29],[30] even if the modulated and unmodulated noises have equal average powers.[31] These findings support the idea that the flanking band reduces masking caused by a speech shaped masker through an across-frequency CMR mechanism. This is consistent with the idea that CMR can produce a modest improvement in the ability to listen selectively in the dips of the masker and/or stream target information present in the dips.[2]

However; performance with CMR was significantly improved in both the hearing aids than UCMR. These findings indicated that both signal processing strategies are effective in identifying signal cues in noise. In contrast to,[25] superior performance of ChannelFree™ in detecting signal embedded in modulated noise is noted. This might be due to the contribution of phoneme level processing strategies offer by the ChannelFree™ hearing aid which may offer the users to utilize their TFS cues in the speech perception in competing signal to detect the signal in fluctuating background noise.

Again this notable difference in CMR and UCMR are evidently seen even when the NR was on in both the hearing aids, though ChannelFree™ performances are >3 channel hearing aids. Hence, all together this provides a through idea that hearing aid users can precisely detect the signal in background noise with the help of NR strategies, especially when the background noise is amplitude modulated. And there is a superior performance of ChannelFree™ in signal detection in noisy conditions which suggest that the novel techniques in amplification devices are always necessary in order to compensate their poor speech understanding in difficulty in listening conditions. But the lack of literature on ChannelFree™ hearing aid and the kind of NR implemented in their hearing aid limits our explanation for predicting the possible reason for superior performance of ChannelFree™ hearing aids for signal detection in background noise when the NR was activated.

Even in the subjective speech quality rating, ChannelFree™ hearing aids were superior in their preference. This may be due to its quick signal processing strategies, thereby it provides gain adjusted up to 20,000 times per se cond. The types of compression may contribute for their differential performance. Because the currently using wide dynamic range of compression (WDRC) multichannel hearing aids use syllabic compression, whereas the ChannelFree™ devices utilized phonemic compression. It helps in providing “temporal coherence,” cue between acoustic components, even when they are spectrally remote. Among the participants, ChannelFree™ hearing aids were mostly preferred by the first time users in comparison to experienced users. The reason might be that the performance of ChannelFree™ hearing aids matches with the expectation level of the first time users in terms of clarity as well understanding signal in the presence of noise.

Whereas the probable reason in experienced users for preferring multichannel hearing aid over ChannelFree™ hearing aids is mainly due to the acclimatization period. Acclimatization period is the average length of time a patient may require to become accustomed to their hearing aids [16] which deliver completely different signal out when comparing with normal acoustic signal. This concept is again supporting with the previous studies [32],[33] and which is vital for achieving good speech intelligibility in noisy conditions.[32] Along with this, individual characteristics such as personality, motivation, and expectations also can determine the acclimatization period.[34] This can be the probable reason for the variability in subjective satisfaction with the hearing aids in speech quality. This also suggest psychophysical characterizes of hearing aid uses where they adamant and comfortable toward their own hearing aid when compared to the experimental conditions. Hence, experienced users are not in a position to draw a conclusion on whether ChannelFree™ hearing aid is better in comparison to what they have been using measured right after the fitting.[32]

The current study results demonstrate that hearing impaired individuals are getting appreciable benefits with ChannelFree™ hearing aids in providing temporal cues for the detection of signal in background noise, especially when the noise is amplitude modulated. This improvement was chiefly noticed when the NR was activated. Participants also reports high satisfaction with the ChannelFree™ hearing aids.

Hence, the main picture emerged from this study is that both phoneme level signal processing and NR strategies offered by the ChannelFree™ hearing aids are very helpful in identifying signal in background noise. Hence, it can improve their speech quality in the daily listening conditions. Though the effects of acclimatization are also play a vital role. Overall, updating and implementing the validated novel technologies to the hearing impaired individual is always necessary.

Acknowledgment

This work was supported by Mr. Arivudai Bambi P (Selection Grade, Department of Audiology and Speech Language Pathology, Kasturba Medical College, Manipal University, Mangalore, India) for providing us with CMR stimuli, MATLAB functions, and also helping us in analyzing the data.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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This article has been cited by
1 Temporal processing and speech perception through multi-channel and channel-free hearing aids in hearing impaired
Kishan Madikeri Mohan,Bellur Rajashekhar
International Journal of Audiology. 2019; : 1
[Pubmed] | [DOI]



 

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