Abstracts
Purpose
To evaluate and compare the performance of elderly people in speech recognition tests, in silence and in noise, using hearing aids with and without the activation of the nonlinear compression algorithm (NLFC).
Methods
Forty-eight subjects were evaluated, 33 male and 15 female, ranging in age from 61 to 84 years, with mild to moderate hearing loss of descending configuration. The Lists of Sentences in Portuguese (LSP) test was applied, seeking the Sentence Recognition Threshold in Silence (SRTS), the Sentence Recognition Threshold in Noise (SRTN), expressed by the signal-to-noise ratio (S/N) and the Sentence Recognition Percentage Index in Silence (SRPIS) and in noise (SRPIN). All measurements were obtained twice: with the use of hearing aids without the activation of NLFC (SC) and with the activation of the NLFC (CC).
Results
It was found a statistically significant difference between the SRTS and PSRS obtained using hearing aids without and with CNLF, the latter being those that provided better results. In the S/N ratio and ISRN the analysis pointed no significant difference between the use of hearing aids SC and CC.
Conclusion
In the measurements obtained in silence, the hearing aids with NLFC CC presented statistically better results than with NLFC SC. In the measurements with competitive noise, it was not found a statistically significant difference between the results obtained with the use of hearing aids SC and CC. This suggests that elderly people with hearing loss of descending configuration could benefit from using hearing aids with NLFC, especially in silence.
Hearing aids; Hearing loss; High-frequency; Aged; Speech discrimination tests; Speech perception
Objetivo
Avaliar e comparar o desempenho de idosos em testes de reconhecimento de fala, no silêncio e no ruído, usando próteses auditivas sem e com a ativação do algoritmo de compressão não linear de frequências (CNLF).
Métodos
Foram avaliados 48 sujeitos, 33 do gênero masculino e 15 do feminino, com idades entre 61 e 84 anos, com perda auditiva de grau leve a moderado e configuração descendente. Aplicou-se o teste Listas de Sentenças em Português (LSP), tendo sido pesquisados os Limiares de Reconhecimento de Sentenças no Silêncio (LRSS) e no Ruído (LRSR), estes últimos expressos pelas Relações Sinal/Ruído (S/R) e Índices Percentuais de Reconhecimento de Sentenças no Silêncio (IPRSS) e no Ruído (IPRSR). Todas as medidas foram obtidas duas vezes, com o uso de próteses auditivas, sem a ativação da CNLF (SC) e com a ativação da CNLF (CC).
Resultados
Observou-se diferença entre os LRSS e IPRSS, obtidos quando usadas próteses auditivas SC e CC, sendo as próteses CC as que proporcionaram melhores resultados. Na relação S/R e IPRSR, não foi observada diferença significativa entre o uso de próteses auditivas SC e CC.
Conclusão
Nas medidas obtidas no silêncio, as próteses auditivas CC apresentaram resultados melhores do que as SC. Nas medidas com ruído competitivo, não foi verificada diferença entre os resultados obtidos com o uso de próteses auditivas SC e CC. Sugere-se que idosos com perda auditiva de configuração descendente podem beneficiar-se do uso de próteses auditivas com CNLF, especialmente no silêncio.
Auxiliares de audição; Perda auditiva de alta frequência; Idoso; Testes de discriminação da fala; Percepção da fala
INTRODUCTION
Over a lifetime, numerous factors can lead to damage in the cochlea, causing hearing loss. Cumulative effects of such factors may cause presbycusis, an age-related hearing loss which, due to the cochlea characteristics, at first is larger in high-frequency than low-frequency sounds, resulting in a descending curve in the audiometric configuration(11 . Jerger S, Jerger J. Alterações auditivas: um manual para avaliação clínica. São Paulo: Atheneu, 1989.).
The effects of presbycusis have impact on speech recognition, considering that
perception of more than 25% of the speech bands are provided by frequencies
starting at 3000 Hz(22 . American National Standards Institute. Methods for the calculation
of the speech intelligibility index. New York: American National Standards
Institute; 2007.). Such
difficulty can be worse in noisy environments, where the bands number decreases
significantly(33 . Caporali SA, Silva JA. Reconhecimento de fala no ruído em jovens e
idosos com perda auditiva. Rev Bras Otorrinolaringol. 2004;70(4):525-32.
http://dx.doi.org/10.1590/S0034-72992004000400014
https://doi.org/10.1590/S0034-7299200400...
).
The amplification of high frequencies with the purpose of enhancing the acoustic information transmitted to an individual and, consequently, improving his/her communication, has been provided to persons with descending hearing loss through adaptation of the hearing aids. However, in this case adaptation tends to be more complex when compared to individuals with other audiometric configurations.
This difficulty may be related to various factors, such as the limitations of
gain and maximum output, mainly at high frequencies, limitations of the
amplification system of the hearing aids and the risk of occurring acoustic
feedback or discomfort due to the high levels of the prescribed sound pressure,
especially at frequencies over 3000 Hz(44 . Bohnert A, Nyffeler M, Kelmann A. Advantages of a non-linear
frequency compression algorithm in noise. Eur Arc Otorhinolaryngol.
2010;267(7):1045-53.
http://dx.doi.org/10.1007/s00405-009-1170-x
https://doi.org/10.1007/s00405-009-1170-...
,55 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T.
Evaluation of nonlinear frequency compression for school-age children with
moderate to moderately severe hearing loss. J Am Acad Audiol.
2010;21(10):618-28. http://dx.doi.org/10.3766/jaaa.21.10.2
https://doi.org/10.3766/jaaa.21.10.2...
).
The technical limitations of conventional hearing aids eventually lead to restricted benefits and satisfaction of individuals with descending hearing loss, users of hearing aids, which led researchers to develop a number of new technologies, based on the same core idea: moving high-frequency hearing information to be perceived at low frequencies.
One of the resources of the hearing aids marketed today is nonlinear frequency
compression (NLFC). It is an algorithm based on two parameters set by the
professional: cut-off frequency (COF) and frequency compression ratio
(CR)(66 . McDermott HJ. A technical comparison of digital frequency-lowering
algorithms available in two current hearing aids. PloS One. 2011;6(7):1-6.
http://dx.doi.org/10.1371/journal.pone.0022358
https://doi.org/10.1371/journal.pone.002...
).
COF consists of the frequency at which NLFC begins to occur. Thus, the algorithm
acts only on the high frequencies, preserving all those below COF, preventing
the overlap of the compressed wave and low-frequency sounds. The amount of
compression is progressive, i.e., frequencies above COF will be more compressed
than those closer to it(66 . McDermott HJ. A technical comparison of digital frequency-lowering
algorithms available in two current hearing aids. PloS One. 2011;6(7):1-6.
http://dx.doi.org/10.1371/journal.pone.0022358
https://doi.org/10.1371/journal.pone.002...
).
Although researches have been carried out using frequency compression in
populations, such as in children and adults already using conventional hearing
aids(44 . Bohnert A, Nyffeler M, Kelmann A. Advantages of a non-linear
frequency compression algorithm in noise. Eur Arc Otorhinolaryngol.
2010;267(7):1045-53.
http://dx.doi.org/10.1007/s00405-009-1170-x
https://doi.org/10.1007/s00405-009-1170-...
,55 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T.
Evaluation of nonlinear frequency compression for school-age children with
moderate to moderately severe hearing loss. J Am Acad Audiol.
2010;21(10):618-28. http://dx.doi.org/10.3766/jaaa.21.10.2
https://doi.org/10.3766/jaaa.21.10.2...
,77 . Simpson A, Hersbach AA, McDermott HJ. Improvements in speech
perception with an experimental nonlinear frequency compression hearing device.
Int J Audiol. 2005;44(5):281-92.
http://dx.doi.org/10.1080/14992020500060636
https://doi.org/10.1080/1499202050006063...
8 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
-99 . Glista D, Scollie S, Bagatto M, Seewald R, Parsa V, Johnson A.
Evaluation of nonlinear frequency compression: clinical outcomes. Int J Audiol.
2009;48(9):632-44. http://dx.doi.org/10.1080/14992020902971349
https://doi.org/10.1080/1499202090297134...
), benefits from this algorithm
have not been yet clarified, especially for elderly persons having no prior
experience in the use of hearing devices.
Aiming to contribute with the literature and the selection of the best procedures for the elderly hearing-impaired persons and to enhance their quality of life and communication, this study aimed to evaluate and compare the performance of elderly persons in speech recognition tests, either in silence or noise, using hearing aids with and without activation of the nonlinear frequency compression algorithm.
METHODS
This research was approved by the Committee for Ethics and Human Research of the Universidade Federal de Santa Maria (UFSM), process nº 05765712.3.0000.5346, and is part of a project registered at the Projects Office under no. 032630. All subjects who agreed to participate signed the Free and Informed Consent Form.
It is a cross-sectional, quantitative, observational and descriptive study. To select the samples, the personal data and audiologic assessments, as described in the medical records of all subjects who came to the Núcleo de Seleção e Adaptação de Próteses Auditivas (NUSEAPA) (Center for Selection and Adaptation of Hearing Aids) to initiate the selection process for adaptation of hearing aids in the period of August 2012 to January 2013, were analyzed.
A total of 275 medical records were examined, and the criteria for inclusion in the sample were: age over 60 years (elderly); having mild to moderate sensorineural hearing loss(1010 . Lloyd LL, Kaplan H. Audiometric interpretation: a manual of basic audiometry. Baltimore: University Park Press; 1978.) and post-lingual-acquired descending configuration(1111 . Silman S, Silverman CA. Auditory diagnostics: principles and applications. San Diego: Singular; 1997.), having Speech Recognition Rate (SRR) of 60% at least without hearing aids; and having never used hearing devices.
Based on these criteria, 49 subjects were contacted by phone to participate in the research and schedule an appointment for the evaluation.
The criteria for exclusion were: history of neurological alteration, cognitive and/or articulatory factors that could interfere in the evaluation or excessive cerumen, or other alterations observed during the visual inspection of the ear canal.
Of the 49 individuals evaluated, one was excluded from the sample for having
score below the cut-off on the Mini Mental State Examination (MMSE)(1212 . Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”. A
practical method for grading the cognitive state of patients for the clinician.
J Psychiatr Res. 1975;12(3):189-98.
http://dx.doi.org/10.1016/0022-3956(75)90026-6
https://doi.org/10.1016/0022-3956(75)900...
), indicating a possible
alteration in the cognitive area.
So, the sample was comprised of 48 individuals, 33 male and 15 female and aged between 61 and 84 years, with sloping hearing loss (Figure 1).
Mean and standard deviation of pure-tone thresholds of the left and right ears of the elderly subjects studied
Data was collected between October 2012 and March 2013 at the Laboratory of Hearing Aids (Laboratório de Próteses Auditivas - LPA), at Universidade Federal de Santa Maria in a single assessment session. The subjects were submitted to anamnesis, application of MMSE and visual inspection of the external auditory meatus before the procedures with the use of hearing aids started.
Everyone was assessed using hearing aids binaurally, of the same brand and model, behind-the-ear type, with digital technology with six adjustment channels, output and maximum gain of 128 dB and 58 dB (2 cc coupler), respectively. Such hearing aids had NLFC activation and deactivation feature and provided two parameters for adjustment of the algorithm, jointly regulated: COF chosen of 1.5 to 6 KHz and CR range between 1.5:1 and 4:1.
Taking into account that all participants had bilateral descending hearing impairment, two hearing aids were programmed for each patient, two hearing aids without activation and two with activation of the NLFC algorithm. Programming of all hearing aids, including adjustments of gain and maximum output per frequency was performed prior to the session with the individual, by fast setting of the software, which assumes the best possible configuration for the patient’s conditions. Similarly, COF and CR relating to NLFC were set. Only the acoustic feedback cancellation feature was maintained, and the other algorithms, such as control of occlusion and automatic selection of programs, were disabled. When turned on, the hearing aids were programmed to work in silence and with omnidirectional microphone. It is worth noting that the only differential between the two pairs of hearing aids used in this study was the activation or not of NLFC.
Simple invisible acrylic earmolds were used to fit the hearing aids, and the vent size was determined according to the audiometric configuration of each subject. For the programming of the hearing aids, the NAL-NL1 prescriptive method was used. Probe microphone measurements were performed prior to the tests to check the suitability of the hearing aids and to enable and disable the NLFC algorithm.
Data was collected using the List of Sentences in Portuguese test (LSP)(1313 . Costa MJ. Listas de sentenças em português: apresentação de estratégias de aplicação na audiologia. Santa Maria: Pallotti;1998.), which allowed determining the Speech Recognition Threshold in Silence (SRTS) and in Noise (SRTN) and the Speech Recognition Percentage Index in Silence (SRPIS) and in Noise (SRPIN).
Measurements were performed in free field, in a soundproof booth using a two-channel digital audiometer, Fonix Hearing Evaluator®, FA 12 model, type I. The sentences were presented by Compact Disc Player Digital Toshiba®, model 4149, connected to the audiometer.
In order to maintain the conditions of reception constant before starting the test, the output of each VI-Meter channel of the audiometer was calibrated, setting it at zero, both the pure tone present in the first band of channel 1 and the noise present in channel 2.
To determine the SRTS and SRTN the material was applied following the procedure
called “sequential, adaptive or ascending-descending strategy”(1414 . Levitt H, Rabiner LR. Use of a sequential strategy in
intelligibility testing. J Acoust Soc Am. 1967;42(3):609-12.
http://dx.doi.org/10.1121/1.1910630
https://doi.org/10.1121/1.1910630...
). According to this strategy,
when the subject was able to correctly recognize the speech stimulus delivered,
the stimulus intensity is reduced; otherwise it is increased. A response was
only considered correct if the subject repeats the sentence without error or
omission.
The step sizes of the sentences presentation, as recommended in the
literature(1414 . Levitt H, Rabiner LR. Use of a sequential strategy in
intelligibility testing. J Acoust Soc Am. 1967;42(3):609-12.
http://dx.doi.org/10.1121/1.1910630
https://doi.org/10.1121/1.1910630...
), are 4
dB in the first sentences until the first change in the response type, after
which a step size of 2 dB is employed. However, the equipment used in this
experiment did not have the feature of step sizes of 4 dB and 2 dB. Therefore, 5
dB and 2.5 dB, respectively, were used. The values of presentation of each
sentence were recorded in the test protocol, and subsequently the means were
calculated based on the intensity of the sentences presentation after the first
change in the response type. This procedure was employed both for the thresholds
of hearing in silence and in noise. In the competitive noise testing it was held
constant in 65 dB SPL (A).
Taking into account that the author(1515 . Cóser PL, Costa MJ, Cóser MJ, Fukuda Y. Reconhecimento de sentenças no silêncio e no ruído em portadores de perda auditiva induzida pelo ruído. Rev Bras Otorrinolaringol. 2000;66(4):362-70.) of the procedure observed a difference of 7 dB in the recording volume between the speech and the noise (speech below the noise level), it was adopted as a procedure for calculation of SRTS and SRTN the subtraction of 7 dB from the speech values recorded in the equipment dial.
So, the SRTS and SRTN were determined, and the latter was expressed by the signal/noise ratio (S/N), which is the difference between the level of presentation of the sentences and the noise. Therefore, for calculation of the S/N ratio, the mean value of the speech presentation levels was subtracted from the noise level. So, whenever the speech is presented below the noise level, the result will be negative, and whenever the speech is presented above the noise level, it will be positive.
For determination of SRPIS and SRPIN, the intensity of the sentences presentation was held constant at the threshold found in the SRTS and SRTN tests of each individual, when he/she was using hearing aids without activation of the NLFC algorithm. A list of sentences was presented for each condition, and during the test the response of the patients was recorded in a protocol, which allowed the analysis of the scores. It was considered as error only the word(s) omitted or repeated incorrectly(1616 . Costa MJ, Santos SN, Lessa AH, Mezzomo CL. Nova proposta de cálculo do índice percentual de reconhecimento de sentenças. CoDAS, no prelo. 2014.).
All measurements of the LSP test were performed using hearing aids, and each subject underwent SRTS, SRTN, SRPIS and SRPIN tests twice: using the hearing aids with NLFC activated and NLFC deactivated. For clarity, the letters SC will follow the measures obtained with hearing aids with NLFC disabled, and with CC letter with NFLC enabled.
Initially, the subjects were tested with hearing aids without activation of NLFC. Prior to the evaluation, all subjects underwent a pre-familiarization test in which the first five sentences of list 7B, without competitive noise, were presented. To facilitate the recognition of the first sentence of each list and in order to make sure that the test was understood, during training the initial intensity of the presentation of the sentences in silence was 10-20 dB above the Speech Recognition Threshold (SRT)(1717 . Henriques MO, Miranda EC, Costa MJ. Limiares de reconhecimento de sentenças no ruído, em campo livre: valores de referência para adultos normo-ouvintes. Rev Bras Otorrinolaringol. 2008;74(2):188-92.). Then, the first ten sentences of list 1A were used for the SRTS SC. With the presentation level set at the value found in the SRTS SC test, the SRTN SC test was carried out using list 1B.
Still using the hearing aids without NLFC activation, measurements were obtained in the presence of competitive noise at a constant level of 65 dB SPL (A). The last five sentences of list 7B were used for training with competitive noise. In this case, the initial intensity of the sentences presentation was 10-20 dB above noise. After training, the list 2B was presented for the SRTS SC testing. With the intensity set at the value found in the SRTN SC, the SRPIN SC was investigated by using the list 3B.
Subsequently, the measurements were calculated following the same parameters for testing with hearing aid with activation of NLFC. Training was performed with the same sentences, either in silence or in noise, and because it was training the repetition of the sentences would not affect the results.
After training in silence, the sentences 11 to 20 of list 1A were used for determination of SRTS CC. In order to maintain the same intensity used in the test without NLFC activation and further comparison of the results, the SRPIS CC was investigated at the same intensity found in the SRTS SC. The list used for the SRPIS CC was 4B. Then, training was performed in noise conditions for further determination of SRTN CC, using list 5B. Just as in the silence test, to find out the SRPIN CC, intensity was set at the value found in SRTN SC, and list 6B was used.
In order to avoid labeling effects similar to the ones of placebo, the sample was blinded with respect to the hearing aids assessed at each test, i.e., the patient did not know whether he/she was assessed with hearing aids with NLFC activated or deactivated.
The data was analyzed descriptively and was submitted to statistical treatment by the Statistica 9.0 software. Checking for the variables normality was made using Shapiro Wilk test. Because they had normal distribution, the variables SRTS, SRPIS and SRPIN were analyzed using the paired t-test for two dependent samples. Wilcoxon non-parametric test was used to analyze the S/N ratio variable, which indicated non-normal distribution.
The confidence interval was stated at the 95% level (p<0.05), and the results that showed significance were indicated by an asterisk (*).
RESULTS
The descriptive measurements and comparative results of SRTS and SRPIS of subjects using hearing aids with and without NLFC activation are shown in Table 1.
A significant difference was observed between the SRTS and SRPIS found with hearing aids with and without NLFC activation. In both measurements, CC hearing aids were the ones that showed better results.
Figures 2 and 3 illustrate the SRTS and SRPIS results for each individual using hearing aids with and without NLFC activation.
Based on the SRTS data, it was observed that 13 individuals presented similar results with SC and CC hearing aids; 25 patients showed improvement of speech recognition and ten presented worsening when using CC hearing aids.
Based on the SRPIS data, it was found that four subjects had similar results using SC and CC hearing aids; 29 patients showed better results and 15 showed worse results d with the use of CC hearing aids.
The descriptive measures and the comparative tests of SRTN, expressed by the S/N ratio and SRPIN of the subject using SC and CC hearing aids, are described in Table 2.
No significant difference between the S/N ratios and SRPIN was found with the use of SC and CC hearing aids.
Figures 4 and 5 show the S/N ratio and SRPIN of each individual using SC and CC hearing aids.
Considering the data resulting from the S/N ratio, it was found that 16 subjects showed similar results using SC and CC hearing aids; 19 showed improvement and 13 a decline in the S/N ratio with the use of CC hearing aids.
Considering the data resulting from the SRPIN, it was observed that two subjects showed similar results using SC and CC hearing aids; 26 had improvement and 20 showed a decrease with the use of CC hearing aids.
DISCUSSION
The aim of this study was not to compare the performance of elderly people with adults or children, but taking into account that there is very little literature associating the algorithm with old ages, the findings of this study were compared with studies covering other ages and similar frequency lowering resources.
The results found in silent condition (Table
1), which presented significant differences between the use of
hearing aids with NLFC activated or deactivated, are in agreement with studies
conducted with children and adults in which the NLFC contributed to an improved
audibility of pitches at 4, 6 and 8 kHz(55 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T.
Evaluation of nonlinear frequency compression for school-age children with
moderate to moderately severe hearing loss. J Am Acad Audiol.
2010;21(10):618-28. http://dx.doi.org/10.3766/jaaa.21.10.2
https://doi.org/10.3766/jaaa.21.10.2...
) and an improved ability to identify the /s/ and /sh/
phonemes and recognize monosyllables, consonants and plurals(77 . Simpson A, Hersbach AA, McDermott HJ. Improvements in speech
perception with an experimental nonlinear frequency compression hearing device.
Int J Audiol. 2005;44(5):281-92.
http://dx.doi.org/10.1080/14992020500060636
https://doi.org/10.1080/1499202050006063...
,99 . Glista D, Scollie S, Bagatto M, Seewald R, Parsa V, Johnson A.
Evaluation of nonlinear frequency compression: clinical outcomes. Int J Audiol.
2009;48(9):632-44. http://dx.doi.org/10.1080/14992020902971349
https://doi.org/10.1080/1499202090297134...
).
On the other hand, the present study is not in agreement with a research that
evaluated in adults the ability to recognize monosyllables and consonants in
silence, comparing the conventional amplification with that in which NLFC was
activated, and no significant difference was found(88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
).
Other frequency-lowering methods, e.g., transposition, showed good results in
silence in experiments conducted with adult and elderly persons, with improved
detection and recognition of fricatives and other consonantal sounds(1818 . Robinson JD, Baer T, Moore BC. J. Using transposition to improve
consonante discrimination and detection for listeners with severe high-frequency
hearing loss. Int J Audiol. 2007;46(6):293-308.
10.1080/14992020601188591
https://doi.org/10.1080/1499202060118859...
19 . Robinson JD, Stainsby TH, Baer T, Moore BCJ. Evaluation of a
frequency transposition algorithm using wearable hearing aids. Int J Audiol.
2009;48(6):384-93. 10.1080/14992020902803138
https://doi.org/10.1080/1499202090280313...
-2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of
linear frequency transposition on consonant identification in quiet and in
noise. J Am Acad Audiol. 2009;20(8):465-79.).
It should be noted that most of the studies mentioned earlier were conducted with subjects with prior experience in the use of hearing aids, often users of conventional amplification. In addition, they were longitudinal researches in which the subjects had had previous home experience with the use of NLFC, which facilitated the adaptation to the new compressed signal. The evaluations were made during this period.
A compilation of the findings of this study with others would indicate that the algorithm has shown goods results in silence anyway. So, it can be seen that the in new signal processing devices and because the sound reception is not so natural, this is overcome by using the residual hearing more effectively. In addition, by making sounds audible even at higher frequencies, which are not in the range of the adaptation frequency of conventional hearing aids, NLFC provides increased transmission of high-frequency acoustic information to be perceived at low frequencies. So, besides restoring the audibility of high frequencies or because of this there is also improved speech recognition, as found in this study.
Because the SRPIS has been evaluated with the same value found in the SRTS, which corresponds to approximately 50% of the correct responses in the sentences recognition, it can be stated that the perception of the individual with respect to the intensity of presentation of the sentences was relatively low. Thus, the positive measures with the use of NLFC, when compared to conventional amplification, corroborate the idea that NLFC can be a feature that enhances audibility of soft sounds where other adjustments, due to limitations of gain or occurrence of acoustic feedback, for example, were not efficient. Positive responses to low-pitched sounds have been reported earlier by other studies(2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of linear frequency transposition on consonant identification in quiet and in noise. J Am Acad Audiol. 2009;20(8):465-79.,2121 . Auriemmo J, Kuk F, Lau C, Marshall S, Thiele N, Pikora M et al. Effect of linear frequency transposition on speech recognition and production of school-age children. J Am Acad Audiol. 2009;20(5):289-305.).
The number of subjects who achieved better results with NLFC was nearly twice as much of those with conventional amplification. Furthermore, the fact that in some cases the extension of the benefit received from the use of the algorithm has been irrefutable evidence, the positive effects of NLFC would not be accomplished with conventional amplification of high frequencies, due to the limitations already known.
Whereas in the present study more than 60% of the subjects presented some
improvement in speech recognition when using hearing aids with NLFC, in an
experiment carried out with 17 subjects using the same resource, eight of them,
which corresponds to 47% of the sample, showed significant improvement of
phonemes recognition when the algorithm was used(77 . Simpson A, Hersbach AA, McDermott HJ. Improvements in speech
perception with an experimental nonlinear frequency compression hearing device.
Int J Audiol. 2005;44(5):281-92.
http://dx.doi.org/10.1080/14992020500060636
https://doi.org/10.1080/1499202050006063...
). In another study, the improvement in hearing
corresponded to half of that found in this research: 22 subjects were evaluated
in the identification of /s/ and /sh/ and only seven, i.e., 30% showed
improvement. Also, in the recognition of plurals, the index increased to 35% of
subjects who showed improved hearing and dropped to 19% in the evaluation of
consonants recognition(99 . Glista D, Scollie S, Bagatto M, Seewald R, Parsa V, Johnson A.
Evaluation of nonlinear frequency compression: clinical outcomes. Int J Audiol.
2009;48(9):632-44. http://dx.doi.org/10.1080/14992020902971349
https://doi.org/10.1080/1499202090297134...
).
The difference between the reported individual improvement rates increases when
compared to studies conducted with five or seven subjects, in which only 20% and
14%, respectively, showed improved recognition of monosyllables and consonants
when experiencing frequency-lowering methods(88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
,1919 . Robinson JD, Stainsby TH, Baer T, Moore BCJ. Evaluation of a
frequency transposition algorithm using wearable hearing aids. Int J Audiol.
2009;48(6):384-93. 10.1080/14992020902803138
https://doi.org/10.1080/1499202090280313...
).
The type of stimulus used to obtain the data of the present research can explain
the greater number of subjects who benefitted from NLFC, compared to other
studies. Reported distortions of consonantal sounds, especially fricatives, and
confusion between phonemes, as described by other studies(88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
,1818 . Robinson JD, Baer T, Moore BC. J. Using transposition to improve
consonante discrimination and detection for listeners with severe high-frequency
hearing loss. Int J Audiol. 2007;46(6):293-308.
10.1080/14992020601188591
https://doi.org/10.1080/1499202060118859...
,1919 . Robinson JD, Stainsby TH, Baer T, Moore BCJ. Evaluation of a
frequency transposition algorithm using wearable hearing aids. Int J Audiol.
2009;48(6):384-93. 10.1080/14992020902803138
https://doi.org/10.1080/1499202090280313...
),
were not common in this research. As the patients were evaluated by means of
sentences, the linguistic context of the phoneme might have facilitated the
distinction from other phonemes that could become similar after compression. A
typical example of such confusion occurs between /sh/ and /s/, where the first
phoneme has dominant energy between 2000 and 4000 Hz, which corresponds to the
frequency range in which the phoneme /s/ will be audible after frequencies
lowering(2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of
linear frequency transposition on consonant identification in quiet and in
noise. J Am Acad Audiol. 2009;20(8):465-79.).
In spite of that, it is believed that the type of stimulus used will not invalidate the favorable results of NLFC. On the contrary, it values them in that the sentences simulate better the daily communication situations to which the patient will be exposed.
The worst performances presented by some individuals, when evaluated with the use of hearing aids with NLFC, may be explained by a series of individual factors, such as educational level, cognition and hearing abilities, among others.
Authors point out that data analysis, such as the frequency in which hearing loss
becomes more severe and the difference of thresholds by octave would help the
interpretation of individual performance differences, once the subjects with a
steep slope in the audiometric curve tend to obtain fewer benefits than those
with moderate decline(77 . Simpson A, Hersbach AA, McDermott HJ. Improvements in speech
perception with an experimental nonlinear frequency compression hearing device.
Int J Audiol. 2005;44(5):281-92.
http://dx.doi.org/10.1080/14992020500060636
https://doi.org/10.1080/1499202050006063...
,88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
). The CR analysis also becomes
interesting because the higher the CR applied the greater the distortion of the
sound signal and, likely, the worse the subjects’ performance(88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
). Thus, these aspects should be
taken into consideration in future studies.
With respect to the data relating to the speech recognition in silence, it should
be taken into account that they were obtained in the first contact with the
patients using hearing aids. Some authors emphasize that due to the spectral
alterations caused by NLFC, the period of acclimatization may be longer than
that with conventional hearing aids. Their studies reported an improvement in
the aspects assessed after using the algorithm for some months(99 . Glista D, Scollie S, Bagatto M, Seewald R, Parsa V, Johnson A.
Evaluation of nonlinear frequency compression: clinical outcomes. Int J Audiol.
2009;48(9):632-44. http://dx.doi.org/10.1080/14992020902971349
https://doi.org/10.1080/1499202090297134...
,2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of
linear frequency transposition on consonant identification in quiet and in
noise. J Am Acad Audiol. 2009;20(8):465-79.,2222 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T et
al. Long-term effects of non-linear frequency compression for children with
moderate hearing loss. Int J Audiol. 2011;50(6):396-404.
10.3109/14992027.2010.551788
https://doi.org/10.3109/14992027.2010.55...
). In
addition, they pointed that in some cases training is important to help users to
be familiarized with the new speech signal(1818 . Robinson JD, Baer T, Moore BC. J. Using transposition to improve
consonante discrimination and detection for listeners with severe high-frequency
hearing loss. Int J Audiol. 2007;46(6):293-308.
10.1080/14992020601188591
https://doi.org/10.1080/1499202060118859...
,1919 . Robinson JD, Stainsby TH, Baer T, Moore BCJ. Evaluation of a
frequency transposition algorithm using wearable hearing aids. Int J Audiol.
2009;48(6):384-93. 10.1080/14992020902803138
https://doi.org/10.1080/1499202090280313...
,2323 . Baskent D, Shannon RV. Frequency transposition around dead regions
simulated with a noiseband vocoder. J Acoust Soc Am. 2006;119(2):1156-63.
http://dx.doi.org/10.1121/1.2151825
https://doi.org/10.1121/1.2151825...
). Therefore, it is believed
that after acclimatization the results would be even better.
The results found in competitive noise conditions (Table 2), which shows that there was no significant
difference in the performance with the use of hearing aids with the NLFC
activated or deactivated, agree with the findings of previous studies, in which
the performance of hearing aids with frequency lowering was similar to that of
conventional devices, and in noise conditions several tests also used sentences
as stimulus(55 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T.
Evaluation of nonlinear frequency compression for school-age children with
moderate to moderately severe hearing loss. J Am Acad Audiol.
2010;21(10):618-28. http://dx.doi.org/10.3766/jaaa.21.10.2
https://doi.org/10.3766/jaaa.21.10.2...
,88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
,1919 . Robinson JD, Stainsby TH, Baer T, Moore BCJ. Evaluation of a
frequency transposition algorithm using wearable hearing aids. Int J Audiol.
2009;48(6):384-93. 10.1080/14992020902803138
https://doi.org/10.1080/1499202090280313...
).
Still, some authors reported that frequency lowering might compromise the speech
recognition in noise(2424 . McDermott HJ, Knight MR. Preliminary results with the AVR impact
frequency-transposing hearing aid. J Am Acad Audiol.
2001;12(3):121-7.).
Hypotheses have been made as to possible disadvantages in using this technology
in such situations. One of them would be that high-frequency noises, not audible
before, would be perceived, making the new S/N ratio not sufficient to enhance
the speech recognition by listeners(55 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T.
Evaluation of nonlinear frequency compression for school-age children with
moderate to moderately severe hearing loss. J Am Acad Audiol.
2010;21(10):618-28. http://dx.doi.org/10.3766/jaaa.21.10.2
https://doi.org/10.3766/jaaa.21.10.2...
).
An alternative to overcome such aspects would be the use of frequency
transposition/compression, developed to act specifically on fricative and/or
affricative consonants(1818 . Robinson JD, Baer T, Moore BC. J. Using transposition to improve
consonante discrimination and detection for listeners with severe high-frequency
hearing loss. Int J Audiol. 2007;46(6):293-308.
10.1080/14992020601188591
https://doi.org/10.1080/1499202060118859...
,2525 . Fraga FJ, Prates LPCS, Iorio MCM. Frequency
compression/transposition of fricative consonants for the hearing impaired with
high-frequency dead regions. In: Proceedings of 9th Annual Conference of the
International Speech Communication Association 2008 (Interspeech. 2008); 2008
Sep 22-26; Brisbane, Austrália. Baixas, France: International Speech
Communications Association; 2009. Vol.1, p. 2238-41.). Although one of the studies
had resulted in greater mishearing of phonemes after using this
resource(1818 . Robinson JD, Baer T, Moore BC. J. Using transposition to improve
consonante discrimination and detection for listeners with severe high-frequency
hearing loss. Int J Audiol. 2007;46(6):293-308.
10.1080/14992020601188591
https://doi.org/10.1080/1499202060118859...
), another
work, developed by Brazilian researchers, had good results in normal-hearing
individuals and in simulation of dead zones in the cochlea, in high
frequencies(2525 . Fraga FJ, Prates LPCS, Iorio MCM. Frequency
compression/transposition of fricative consonants for the hearing impaired with
high-frequency dead regions. In: Proceedings of 9th Annual Conference of the
International Speech Communication Association 2008 (Interspeech. 2008); 2008
Sep 22-26; Brisbane, Austrália. Baixas, France: International Speech
Communications Association; 2009. Vol.1, p. 2238-41.).
However, NLFC still is an alternative that after acclimatization may provide
greater satisfaction and benefits in speech recognition by subjects with
descending hearing loss, even in acoustically unfavorable environments. This is
corroborated by previous studies that revealed that the daily exposure to the
compressed signal by patients using hearing aids with frequency lowering could
lead them to recognize more easily the altered signal in noise(44 . Bohnert A, Nyffeler M, Kelmann A. Advantages of a non-linear
frequency compression algorithm in noise. Eur Arc Otorhinolaryngol.
2010;267(7):1045-53.
http://dx.doi.org/10.1007/s00405-009-1170-x
https://doi.org/10.1007/s00405-009-1170-...
,2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of
linear frequency transposition on consonant identification in quiet and in
noise. J Am Acad Audiol. 2009;20(8):465-79.,2222 . Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T et
al. Long-term effects of non-linear frequency compression for children with
moderate hearing loss. Int J Audiol. 2011;50(6):396-404.
10.3109/14992027.2010.551788
https://doi.org/10.3109/14992027.2010.55...
).
As clearly demonstrated by researchers, the fact that the resource does not show negative effects in in-noise speech recognition may be considered an important and positive finding for using it in situations where speech occurs concurrently with a competitive signal(2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of linear frequency transposition on consonant identification in quiet and in noise. J Am Acad Audiol. 2009;20(8):465-79.). It is believed that with the activation of algorithms and the use of directional microphone to reduce noise, which were deactivated in the present study, the benefits of NLFC in this condition would be greater, especially after the acclimatization period, as mentioned earlier in this study.
The improved S/N ratio and SRPIN of individuals using hearing aids with activated
NLFC (Figures 4 and 5), as found in this study, is similar to
that reported in an experiment conducted with 11 adults and elderly subjects, in
which seven of them had their performance improved in recognizing sentences in
noise with the use of NLFC(44 . Bohnert A, Nyffeler M, Kelmann A. Advantages of a non-linear
frequency compression algorithm in noise. Eur Arc Otorhinolaryngol.
2010;267(7):1045-53.
http://dx.doi.org/10.1007/s00405-009-1170-x
https://doi.org/10.1007/s00405-009-1170-...
).
But in experiments conducted with smaller size samples showed a smaller
proportion of subjects who benefitted from the use of the algorithm, when
exposed to competitive signals(88 . Simpson A, Hersbach AA, McDermott HJ. Frequency-compression
outcomes in listeners with steeply sloping audiograms. Int J Audiol.
2006;45(11):619-29. http://dx.doi.org/10.1080/14992020600825508
https://doi.org/10.1080/1499202060082550...
,1919 . Robinson JD, Stainsby TH, Baer T, Moore BCJ. Evaluation of a
frequency transposition algorithm using wearable hearing aids. Int J Audiol.
2009;48(6):384-93. 10.1080/14992020902803138
https://doi.org/10.1080/1499202090280313...
). It should be
noted that in the present study the benefit provided with the use of the
algorithm was not so pronounced as that observed in silence, which is consistent
with the fact that there was no difference in the analysis of the group, in
noise condition.
It is worth noting that if for young normal individuals speech recognition in competitive noisy environments demands much more effort than in silent environments, for hearing-impaired elderly persons such difficulty is much greater.
For many authors, hearing impairment would not be the primary factor responsible
for the differences in the hearing abilities of adult and elderly
persons(2626 . Liporaci FD, Frota SMMC. Resolução temporal auditiva em idosos.
Rev Soc Bras Fonoaudiol. 2010;15(4):533-9.
http://dx.doi.org/10.1590/S1516-80342010000400010
https://doi.org/10.1590/S1516-8034201000...
27 . Fogerty D, Humes LE, Kewley-Port D. Auditory temporal-order
processing of vowel sequences by young and elderly listeners. J Acoust Soc Am.
2010;127(4):2509-20. http://dx.doi.org/10.1121/1.3316291
https://doi.org/10.1121/1.3316291...
-2828 . Freigang C, Schmidt L, Wagner J, Eckardt R, Steinhagen-Thiessen E,
Emst A, et al. Evaluation of central auditory discrimination abilities in older
adults. Front Aging Neurosci. 2011;3(6):1-11.
http://dx.doi.org/10.3389/fnagi.2011.00006
https://doi.org/10.3389/fnagi.2011.00006...
), but rather the diffuse
effect of aging, which affects the central nervous system and the cortical
processing(2828 . Freigang C, Schmidt L, Wagner J, Eckardt R, Steinhagen-Thiessen E,
Emst A, et al. Evaluation of central auditory discrimination abilities in older
adults. Front Aging Neurosci. 2011;3(6):1-11.
http://dx.doi.org/10.3389/fnagi.2011.00006
https://doi.org/10.3389/fnagi.2011.00006...
).
Although no specific test to evaluate the auditory processing has been applied in
the present research it is well known that elderly persons have difficulty in
the auditory processing of speech signals distorted by noise(2929 . Janse E. Processing of fast speech by elderly listeners. J Acoust
Soc Am. 2009;125(4):2361-73.
http://dx.doi.org/10.1121/1.3082117
https://doi.org/10.1121/1.3082117...
). The results of this study
agree with the above statement since in silence the subjects were able to
benefit from increased acoustic information transmitted with NLFC, even with
distorted signal. But when evaluated in noise, the difficulties in the auditory
processing arising from the aging process became more evident, once in this
condition there were two negative active factors: noise and the distortion from
the new signal processing.
Changes during aging also lead to a decreased functional S/N ratio, requiring adjustments in this ratio with a louder speech signal for the message to be recognized in competitive noise. The findings of this study corroborate the foregoing description, once such adjustment can be provided by NLFC, a fact that was observed in more than 40% of the older persons that showed some improvement when the algorithm was used in noise conditions. It is believed that the elderly persons who had such benefit would likely present better results in tasks of auditory processing than the 30% who had their performance diminished, in the same condition.
Furthermore, it is known that the speech recognition in such situations requires non-auditory abilities, such as attention (focus on a particular sound), inhibitory control (ignoring irrelevant sound) and memory (recalling the speech information). But such abilities may also be impaired with aging(3030 . Glisky E. Changes in cognitive function in human aging. In: David R, editor. Brain aging: models, methods and mechanisms. Boca Raton: CRC; 2007.) and might have impacted negatively the results found in noise.
Considering the reported results, it is believed that hearing training may help
elderly people get used to the distortions caused by NLFC and stimulate their
auditory and non-auditory abilities, which would maximize the advantages that
some of them already had with the use NLFC and even be beneficial to those who
have not shown them yet(1818 . Robinson JD, Baer T, Moore BC. J. Using transposition to improve
consonante discrimination and detection for listeners with severe high-frequency
hearing loss. Int J Audiol. 2007;46(6):293-308.
10.1080/14992020601188591
https://doi.org/10.1080/1499202060118859...
,2020 . Kuk F, Keenan D, Korhonen P, Lau CC. Efficacy of
linear frequency transposition on consonant identification in quiet and in
noise. J Am Acad Audiol. 2009;20(8):465-79.,2323 . Baskent D, Shannon RV. Frequency transposition around dead regions
simulated with a noiseband vocoder. J Acoust Soc Am. 2006;119(2):1156-63.
http://dx.doi.org/10.1121/1.2151825
https://doi.org/10.1121/1.2151825...
).
By comparing the results in conditions of silence (SRPIS) and noise (SRPIN) with NLFC activated, it caught our attention in this research the fact that 14 subjects showed worsening speech recognition in silence, and 11 subjects showed improvement in silence and worsening in noise. It was observed that more than 50% of the sampled subjects showed improvement in the speech recognition with the use of the resource in one condition and worsening in other.
Changes in the auditory processing level that were likely presented by some patients can explain part of the data described above. Also, it should be noted that the hearing aids setting was performed generally and automatically the default program of the software. Therefore, finer adjustments might result in more positive performances in both situations, noise and silence. Even so, the findings suggest that in some cases the use of different programs would be interesting considering the diverse situations to which the patient will be exposed, either with NLFC activated or not.
Considering the above, it can be affirmed that the findings of this study demonstrated that elderly persons are able to deal with changes in signal processing and distortions caused by NLFC, and may also benefit, even in the first time, from the improved audibility provided by the algorithm. Anyway, it should be emphasized that individual aspects such as daily life, occupation, educational level, and hearing and cognitive skills should be taken into consideration when deciding on the use or not of the algorithm.
CONCLUSION
In silence, the use of hearing aids with NLFC provided greater benefits in speech recognition by elderly persons than when using hearing aids without NLFC. In-noise speech recognition by the elderly persons was similar to that using hearing aids with NLFC activated or deactivated.
Based on this study, it can be suggested that elderly persons with sloping hearing loss can benefit from the use of hearing aids with NLFC, especially in silent environments.
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» https://doi.org/10.1080/14992020601188591 -
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» https://doi.org/10.1080/14992020902803138 -
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21Auriemmo J, Kuk F, Lau C, Marshall S, Thiele N, Pikora M et al. Effect of linear frequency transposition on speech recognition and production of school-age children. J Am Acad Audiol. 2009;20(5):289-305.
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22Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T et al. Long-term effects of non-linear frequency compression for children with moderate hearing loss. Int J Audiol. 2011;50(6):396-404. 10.3109/14992027.2010.551788
» https://doi.org/10.3109/14992027.2010.551788 -
23Baskent D, Shannon RV. Frequency transposition around dead regions simulated with a noiseband vocoder. J Acoust Soc Am. 2006;119(2):1156-63. http://dx.doi.org/10.1121/1.2151825
» https://doi.org/10.1121/1.2151825 -
24McDermott HJ, Knight MR. Preliminary results with the AVR impact frequency-transposing hearing aid. J Am Acad Audiol. 2001;12(3):121-7.
-
25Fraga FJ, Prates LPCS, Iorio MCM. Frequency compression/transposition of fricative consonants for the hearing impaired with high-frequency dead regions. In: Proceedings of 9th Annual Conference of the International Speech Communication Association 2008 (Interspeech. 2008); 2008 Sep 22-26; Brisbane, Austrália. Baixas, France: International Speech Communications Association; 2009. Vol.1, p. 2238-41.
-
26Liporaci FD, Frota SMMC. Resolução temporal auditiva em idosos. Rev Soc Bras Fonoaudiol. 2010;15(4):533-9. http://dx.doi.org/10.1590/S1516-80342010000400010
» https://doi.org/10.1590/S1516-80342010000400010 -
27Fogerty D, Humes LE, Kewley-Port D. Auditory temporal-order processing of vowel sequences by young and elderly listeners. J Acoust Soc Am. 2010;127(4):2509-20. http://dx.doi.org/10.1121/1.3316291
» https://doi.org/10.1121/1.3316291 -
28Freigang C, Schmidt L, Wagner J, Eckardt R, Steinhagen-Thiessen E, Emst A, et al. Evaluation of central auditory discrimination abilities in older adults. Front Aging Neurosci. 2011;3(6):1-11. http://dx.doi.org/10.3389/fnagi.2011.00006
» https://doi.org/10.3389/fnagi.2011.00006 -
29Janse E. Processing of fast speech by elderly listeners. J Acoust Soc Am. 2009;125(4):2361-73. http://dx.doi.org/10.1121/1.3082117
» https://doi.org/10.1121/1.3082117 -
30Glisky E. Changes in cognitive function in human aging. In: David R, editor. Brain aging: models, methods and mechanisms. Boca Raton: CRC; 2007.
-
Work carried out at the Nucleus of Selection and Adaptation of Hearing Aids (NUSEAPA), at the Universidade Federal de Santa Maria – UFSM – Santa Maria (RS), Brazil, with scholarship granted by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
Publication Dates
-
Publication in this collection
Sept 2014
History
-
Received
27 Jan 2014 -
Accepted
23 Apr 2014