Scholarly article on topic 'Effect of contralateral stimulation on acoustic reflectance measurements'

Effect of contralateral stimulation on acoustic reflectance measurements Academic research paper on "Medical engineering"

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Academic research paper on topic "Effect of contralateral stimulation on acoustic reflectance measurements"

BrazJ Otorhinolaryngol. 2015;81(5):466-472

Brazilian Journal of



Effect of contralateral stimulation on acoustic reflectance measurements^'^

Tathiany Silva Pichelli*, Jordana Costa Soares, Bruna Carla Cibin, Renata Mota Mamede Carvallo


Faculdade de Medicina, Universidade de Sao Paulo (FM-USP), Sao Paulo, SP, Brazil

Received 16 September 2013; accepted 23 October 2014 Available online 21 July 2015


Hearing; Middle ear; Acoustic reflex; Hearing tests


Introduction: Acoustic reflectance is an important tool in the assessment of middle ear afflictions, and the method is considered advantageous in relation to tympanometry. There has been a growing interest in the study of contralateral acoustic stimulation and its effect on the activation of the efferent auditory pathway. Studies have shown that the introduction of simultaneous stimulation in the contralateral ear generates alterations in auditory response patterns. Objective: To investigate the influence of contralateral stimulation on acoustic reflectance measurements.

Methods: Case study of 30 subjects with normal hearing, of both genders, aged 18-30 years. The test and retest acoustic reflectance was conducted in the frequency range 200-6000 Hz. The procedure was repeated with the simultaneous presence of contralateral white noise at 30 dBNS.

Results: The analysis of the conditions of test, retest, and test with contralateral noise showed statistical difference at the frequency of 2 kHz (p = 0.011 and p = 0.002 in test and retest, respectively) in the right ear.

Conclusion: The activation of the auditory efferent pathways through contralateral acoustic stimulation produces alterations in response patterns of acoustic reflectance, increasing sound reflection and modifying middle ear acoustical energy transfer.

© 2015 Associacao Brasileira de Otorrinolaringologia e Cirurgia Cervico-Facial. Published by Elsevier Editora Ltda. All rights reserved.

* Please cite this article as: Pichelli TS, Soares JC, Cibin BC, Carvallo RMM. Effect of contralateral stimulation on acoustic reflectance measurements. BrazJ Otorhinolaryngol. 2015;81:466-72.

** Institution: Faculdade de Medicina da Universidade de Sâo Paulo (FM-USP), Sâo Paulo, SP, Brazil.

* Corresponding author.

E-mail: (T.S. Pichelli).

1808-8694/© 2015 Associacâo Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Published by Elsevier Editora Ltda. All rights reserved.

Efeito da estimulacao contralateral nas medidas de reflectancia acústica Resumo

Introducao: A reflectancia acústica é citada como uma importante ferramenta na avaliacao das afeccóes da orelha média, sendo um método considerado vantajoso em relacao a timpanome-tria. Tem havido crescente interesse no estudo da estimulacao acústica contralateral e seu efeito na ativacao da via eferente auditiva. Estudos tem demonstrado que a introducao de estímulo simultaneo na orelha contralateral gera mudancas no padrao de respostas auditivas. Objetivo: Verificar a influencia da estimulacao contralateral nas medidas de reflectancia acústica.

Método: Estudo de casos de 30 sujeitos com audicao normal, de os géneros entre 18 a 30 anos. Foi realizado o teste e reteste de reflectancia acústica no intervalo de frequéncia de 200 a 6000 Hz. O procedimento foi repetido com a presenca simultanea de ruído branco contralateral a 30 dBNS.

Resultados: A análise entre as condicóes de teste, reteste e teste com ruído contralateral apresentou diferenca estatística na frequéncia de 2 kHz (p = 0,011 em teste e p = 0,002 em reteste) em orelha direita.

Conclusao: A ativacao da via auditiva eferente por meio da estimulacao acústica contralateral produz mudancas nos padróes de respostas da reflectancia acústica, aumentando a reflexao do som e, modificando a transferencia de energia sonora da orelha média. © 2015 Associacao Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Publicado por Elsevier Editora Ltda. Todos os direitos reservados.


Audicäo; Orelha média; Reflexo acústico; Testes auditivos


The use of acoustic immittance at a frequency of 220 Hz has contributed to the clinical diagnosis of middle ear disorders, especially those associated with a change of stiffness in the system. Several authors have suggested that the use of additional frequencies besides 220 Hz can provide data on the tympanum-ossicular system behavior, especially when stimulated by high tones.1"6

An alternative line of research on middle ear function in adults and children has used measures of acoustic immit-tance in a static pressure environment with a wide range of frequencies.7 They are the so-called admittance and reflectance tests. The acoustic reflectance is the ratio of energy reflected from a surface over the energy that reaches the surface (incident energy). This concept shows how much energy is reflected by the tympanic membrane and how much is absorbed by the middle ear. Acoustic reflectance systems can measure a wide range of frequencies; because the acoustic reflectance is mathematically related to the impedance and admittance, it is possible to derive any quantity of immittance from the reflectance measurements.

Over several years, acoustic reflectance measurements have been described as an important tool in the assessment of middle ear disorders.7"12 Acoustic reflectance measurements have potential advantages over tympanom-etry, particularly in children. First, ear canal pressurization is not necessary, and thus there is no distortion in the canal. Second, the measures are performed over a range of frequencies, instead of a single frequency evaluated in tympanometry. And finally, the measures can be quickly obtained. Therefore, it is possible that the acoustic reflectance measurements can provide more information,

more quickly than tympanometry in the diagnosis of middle ear dysfunctions.

The hearing system consists of auditory afferent and efferent pathways that operate jointly. The auditory efferent pathway has connections from the cortex to the most peripheral structures. In this pathway, the efferent motor neuron systems are highlighted, with the olivocochlear tract responsible for sending fibers to the spiral body and the motor neurons of the middle ear muscles.13"16

There has been a growing interest in the study of contralateral acoustic stimulation and its effect on the auditory efferent pathway activation. Studies have shown that the introduction of simultaneous stimulation in the contralateral ear generates changes in the auditory response patterns, both in otoacoustic emission (OAE) measurements and in auditory evoked potentials (AEP), with a reduction in response amplitude observed.17"20 Simultaneous contralateral stimulation also has been shown to increase acoustic immittance reflex thresholds.21,22

The auditory efferent pathways, through the integrated action of the auditory system, modify the response of the outer hair cells and activate the reflex of the middle ear muscles. This principle gave rise to the hypothesis that acoustic reflectance, being a high-resolution measure, could identify possible changes in the middle ear energy transfer, when the efferent auditory pathway is activated through white noise in the contralateral ear.

There are no similar studies in the literature that have provided clues on the effect of this stimulation on the profile of acoustic reflectance curves. Therefore, the aim of this study is to investigate the influence of contralateral stimulation by white noise on the middle ear acoustic reflectance measurements in young adults.


This was an observational study of a contemporary cohort. The present study was developed in a laboratory of human hearing research, after being approved by the Research Ethics Committee through protocol 212/10.


Participants were recruited among the university students of the teaching and research center of the institution. The sample consisted of 30 participants, 15 males and 15 females, aged 18-30 years. To avoid influence of laterality or cerebral dominance, all subjects showed right lateral dominance according to Edinburgh Inventory.23

Inclusion criteria for this study were: absence of middle ear disorders detected at tympanometry (type A curve) and no history of otitis during childhood nor in the past five years; ipsilateral acoustic reflexes present at the frequencies of 500-4000Hz; and hearing thresholds up to 20dB.


The following were used:

1. Protocol for identification data registry and investigation of complaints related to hearing;

2. GSI 61 - Grason Stadler Audiometer - The equipment complies with the ANSI S 3,6-1989; ANSI S3,43-1992; IEC 645-1(1992); IEC 645-2(1993); ISO 389; and UL 544 standards. Insertion earphones in a calibrated transducer for the ER-Etymotic model were used for threshold audiometry (250-8000 Hz) and white noise threshold assessment.

3. An AT235 micro-processed Middle Ear Analyzer with two tone frequencies in the immittance probe: 226 Hz was used for automatic tympanometric measures at the rate of 50daPa/s, whereas the manual form of equipment was used for the measurements of ipsilateral acoustic reflexes.

4. MEPA3 - Middle-Ear Power Analysis - Mimosa Acoustics - used to obtain the reflectance measurements through the clinical module program MEPA 3, with the following technical characteristics:

Frequency range: 169-6613 Hz

Stimulus intensity: 60dBNPS

Sample time (window): 0.1-10s per point

Stimulus: ''Chirp''

Probe: Etymotic Research ER 10C

Latex eartips in eight adaptable sizes for children and


The MEPA equipment was calibrated in an acoustically treated room and the reflectance test was conducted inside the soundproof booth where audiometry was performed.


Initially the subjects were informed about the study aims and procedures and, after agreeing to participate, they signed the informed consent.

The procedures were performed in a single session lasting approximately 20min. Identification data registry was carried out using a specific protocol and the anamneses included complaints related to hearing and otological history in childhood and the past five years, as the subjects could not have complaints or history of otitis to be included in the study. Next, the subjects were instructed to complete the Edinburgh Inventory to assess laterality or cerebral dominance influence.

After these steps, the subjects were submitted to the following procedures:

1. Inspection of the external auditory meatus.

2. Imitanciometry consisting of tympanometry with probes of 226 and 1000 Hz and acoustic reflex assessment in the ipsilateral and contralateral modalities at 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz.

3. Pure-tone threshold audiometry at the frequencies of 250-8000 Hz at 10-dB down and 5-dB up method, with starting frequency at 1000 Hz, followed by the frequencies of 2000, 3000, 4000, 6000, 8000, 500, and 250 Hz. White noise threshold assessment was performed to define the basal value for the noise input at the same intensity ratio. Thus, the level of 30dB SL (decibel sensation level) was used for noise intensity. The noise was generated by the GSI 61 audiometer and provided through insertion phones in a calibrated transducer for the ER-Etymotic model.

4. Middle ear reflectance assessment in three steps: (A) Obtaining the reflectance curve in the frequency range 200-6000 Hz at an intensity of 60 dB SPL. Each stimulus lasted 0.1-10s per point. Collection was carried out with the chirp acoustic stimulus. (B) Retest to confirm the obtained reflectance curve. (C) The procedure was repeated, with the simultaneous presence of contralateral noise through insertion phones at 30dBNS in relation to the white noise threshold. In the end, three measures were obtained in each ear. Based on the three measures, the difference between the response levels collected with and without contralateral noise was calculated.

Statistical analysis

Data were automatically exported by MEPA equipment to Microsoft Excel software. To determine whether there was a response alteration at each assessed frequency with and without contralateral noise, increase or decrease was considered when the subtraction of values was different from zero.

The variables were submitted to statistical analysis and the 5% significance level was used to reject the null hypothesis for all analyses.


Table 1 and Fig. 1 show the results of the comparative analysis of the different assessment conditions for the chirp stimulus.

Statistical differences were observed at the frequency of 2 kHz for the chirp stimulus in the right ear when comparing the test to the test with contralateral noise, as well as when

Table 1 Descriptive statistics of the acoustic reflectance between the comparisons of test, retest, and test with contralateral noise conditions for the chirp stimulus in the right ear.

Chirp reflectance RE Mean Median Standard deviation CV Min Max n CI

Test 91.81 93.26 5.40 6% 78.42 100.00 30 1.93

250 Hz Retest 91.64 93.29 6.25 7% 75.46 99.39 30 2.24

With noise 91.93 93.05 5.60 6% 76.12 100.00 30 2.01

Test 79.01 79.88 13.37 17% 48.51 99.22 30 4.78

500 Hz Retest 79.28 79.95 13.02 16% 50.24 98.81 30 4.66

With noise 78.79 78.81 12.83 16% 47.46 100.00 30 4.59

Test 61.48 60.71 17.84 29% 23.94 89.06 30 6.38

750 Hz Retest 61.29 59.78 17.72 29% 23.99 88.08 30 6.34

With noise 61.43 60.78 17.97 29% 25.11 88.34 30 6.43

Test 47.32 46.85 18.10 38% 9.09 79.81 30 6.48

1 kHz Retest 47.37 47.35 17.73 37% 9.08 80.22 30 6.34

With noise 47.59 47.05 18.02 38% 8.34 82.08 30 6.45

Test 39.96 40.65 15.80 40% 1.66 64.35 30 5.65

1.5 kHz Retest 39.86 41.23 15.86 40% 2.07 65.28 30 5.68

With noise 39.85 41.09 15.81 40% 3.01 64.80 30 5.66

Test 40.27 45.48 17.62 44% 3.85 75.57 30 6.30

2 kHz Retest 40.30 45.61 17.91 44% 4.01 75.46 30 6.41

With noise 41.10 45.19 17.65 43% 4.66 75.43 30 6.32

Test 36.68 40.06 18.73 51% 3.27 75.51 30 6.70

3 kHz Retest 36.70 39.34 18.83 51% 3.28 75.18 30 6.74

With noise 37.01 38.14 18.72 51% 3.37 75.99 30 6.70

Test 45.56 47.09 17.16 38% 4.16 79.37 30 6.14

4 kHz Retest 45.96 47.12 16.83 37% 4.00 79.57 30 6.02

With noise 45.65 46.70 16.98 37% 5.55 80.46 30 6.08

Test 74.50 77.02 19.32 26% 31.56 105.45 30 6.91

6 kHz Retest 74.95 78.35 19.57 26% 33.00 107.95 30 7.00

With noise 75.05 78.40 19.64 26% 33.51 109.65 30 7.03

RE, right ear; CV, coefficient of variation; n, number of ears; CI, confidence interval.

comparing the retest and the test with contralateral noise, with p-values of 0.011 and 0.002 for the comparisons of the test and the retest, respectively.

Regarding the left ear, there was no statistical difference when comparing the test, retest, and test with contralateral noise situations for the chirp stimulus. The results are shown in Table 2 and Fig. 2.


In the literature the middle ear is classically described as a mechanical-acoustic energy transmitter with a linear characteristic, that both allows the passage of, and some resistance to, sound.7,24 Only at high intensities does the middle ear lose this linear characteristic, as there is a contraction of intratympanic muscles with high sound stimulus situations. The reflex action of these muscles is directly involved in auditory system protection from high intensity sounds.24"26

At the frequency of 2 kHz in the right ear for the chirp stimulus, a statistical difference was observed when comparing the test and retest conditions with the test condition

with contralateral noise. The mean responses increased when the auditory efferent pathway was activated. The resulting inhibitory effect would act as an auditory system protection, making the system increase sound reflection. Thus, the energy transfer through the middle ear is lower, preventing damage to the auditory system and improving noise discrimination, especially in noisy environments, demonstrating that the middle ear may be the first auditory system selection filter, as previously suggested by another study.24 It is noteworthy that these results were observed in right-handed individuals with right side dominance, confirmed by the Edinburgh Inventory. Thus, our study detected an advantage of the right when submitted to auditory efferent pathway activation, as was observed in other auditory system studies.17,27 The discussed subject is whether the same right ear advantage would be observed in left-handed individuals and thus, studies on the subject are necessary.

The WN intensity utilized was 30dBNS, mirroring other studies.21,22 This intensity was used to activate the auditory efferent pathway without activating the acoustic reflexes. The contralateral suppression of the acoustic reflex can be used to verify the efferent pathway function when the auditory system is subjected to high intensity levels,27 but under

Test Retest With noise

Test Retest With noise Test Retest With noise

Figure 1 Box plot of comparisons of responses between test, retest, and test with contralateral noise conditions in the right ear.

Retest With noise

Retest With noise

Test Retest With noise

Figure 2 Box plot of comparisons of responses between test, retest, and test with contralateral noise conditions in the left ear.

Table 2 Statistical analysis of the acoustic reflectance between the comparisons of test, retest, and test with contralateral noise conditions for chirp stimulus in the left ear.

Chirp reflectance LE Mean Median Standard deviation CV Min Max n CI

Test 92.15 93.21 6.80 7% 70.95 100.00 30 2.43

250Hz Retest 91.54 92.29 7.29 8% 72.70 100.00 30 2.61

With noise 90.66 93.06 8.01 9% 66.98 100.00 30 2.87

Test 81.90 82.49 10.90 13% 56.09 100.00 30 3.90

500Hz Retest 81.95 81.20 10.65 13% 56.12 98.78 30 3.81

With noise 81.96 82.23 11.15 14% 55.98 100.00 30 3.99

Test 64.83 66.56 16.23 25% 23.91 93.91 30 5.81

750Hz Retest 64.92 66.56 16.39 25% 23.24 93.43 30 5.87

With noise 64.83 64.82 16.12 25% 24.44 92.96 30 5.77

Test 53.24 53.28 17.73 33% 11.11 85.28 30 6.34

1 kHz Retest 53.22 54.80 18.32 34% 10.78 84.79 30 6.55

With noise 53.51 53.37 18.22 34% 9.67 85.58 30 6.52

Test 44.66 48.37 15.65 35% 9.97 68.72 30 5.60

1.5 kHz Retest 45.18 48.28 15.48 34% 11.20 71.86 30 5.54

With noise 44.84 49.86 16.27 36% 14.47 71.92 30 5.82

Test 40.80 42.73 14.54 36% 9.43 69.17 30 5.20

2 kHz Retest 41.18 42.53 14.33 35% 10.30 69.11 30 5.13

With noise 41.43 43.98 14.77 36% 8.69 70.00 30 5.29

Test 29.35 27.85 15.32 52% 5.16 59.20 30 5.48

3 kHz Retest 29.28 27.64 15.12 52% 4.99 58.19 30 5.41

With noise 29.74 27.47 15.43 52% 6.30 59.52 30 5.52

Test 35.08 28.29 16.75 48% 10.24 77.98 30 5.99

4kHz Retest 34.95 28.24 16.97 49% 10.73 77.78 30 6.07

With noise 35.07 29.26 17.01 48% 12.12 77.87 30 6.09

Test 72.79 72.64 18.32 25% 33.21 100.07 30 6.56

6 kHz Retest 73.02 73.21 18.29 25% 35.86 100.00 30 6.54

With noise 73.25 73.58 18.38 25% 32.34 100.00 30 6.58

LE, left ear; CV, coefficient of variation; n, number of ears; CI, confidence interval.

the influence of contralateral acoustic stimulation, changes in the latency and threshold acoustic reflex responses are observed.21,22 Studies with OAE and AEP used contralateral stimulation level at the intensity of 60 dB HL;20,28"30 however, a study comparing different levels of contralateral stimulation observed that an intensity lower than or equal to 50 dB HL did not affect the clinical recording of N1 and P2 waves.30

The influence of the auditory efferent pathway pervades the entire auditory system, ranging from the most central to the most peripheral portion. Studies with OAE, BAEP (brainstem auditory evoked potential), and medium- and long-latency AEP with contralateral acoustic stimulation provide information that there is an alteration of the responses in these procedures.20,31"34 With the same purpose, but assessing the middle ear, some authors21,22 associated response alterations to the auditory efferent pathway influence on that portion of the auditory system. The findings of this study suggest that the auditory efferent pathway acts on the middle ear causing changes in patterns of acoustic reflectance responses.


When the auditory efferent pathway is stimulated by contralateral acoustic stimulus with white noise, there is a statistical difference at the frequency of 2 kHz in the right ear for the chirp stimulus for both test and retest conditions. This effect consistency shows that the auditory efferent pathway influences acoustic energy transfer by the middle ear, with right-ear advantage and at medium frequency.


This study was funded by the Fundacao de Amparo a Pesquisa e Ensino de Sao Paulo - FAPESP.

Conflicts of interest

The authors declare no conflicts of interest.


1. Jerger JF. Clinical experience with impedance audiometry. Arch Otolaryngol. 1970;92:311-24.

2. Colletti V. Methodological observations on tympanometry with regard to the probe-tone frequency. Acta Otolaryngol. 1975;80:54-60.

3. Holte L, Margolis RH, Cavanaugh RM. Developmental changes in multifrequency tympanograms. Audiology. 1991;30:1-24.

4. Hunter LL, Margolis RH. Multifrequency tympanometry: current clinical application. Am J Audiol. 1992;1:33-43.

5. Linares AE, Carvallo RMM. Medidas imitanciometricas em criancas com ausencia de emissoes otoacusticas. Braz J Otorhi-nolaryngol. 2008;74:410-6.

6. Keefe DH, Ling R, Bulen JC. Method to measure acoustic-impedance and reflection coefficient. J Acoust Soc Am. 1992;91:470-85.

7. Voss SE, Allen JB. Measurement of acoustic impedance and reflectance in the human ear canal. J Acoust Soc Am. 1994;95:372-84.

8. Keefe DH, Folsom RC, Gorga MP, Vohr BR, Bulen JC, Norton SJ. Identification of neonatal hearing impairment: ear-canal measurements of acoustic admittance and reflectance in neonates. Ear Hear. 2000;21:443-61.

9. Margolis RH, Paul S, Saly GL, Schachem PA, Keefe DH. Wideband reflectance tympanometry in chinchillas and humans. J Acoustic Soc Am. 2001;110:1453-64.

10. Feeney MP, Keefe DH, Sanford CA. Wideband reflectance measures of the ipsilateral acoustic stapedius reflex threshold. Ear Hear. 2004;25:421-30.

11. Hunter LL, Tubaugh L, Jackson A, Propes S. Wideband middle ear power measurement in infants and children. J Am Acad Audiol. 2008;19:309-24.

12. Sanford AC, Hunter LL, Feeney MP, Nakajima HH. Wideband acousti immittance: tympanometric measures. Ear Hear. 2013;34:65S-71S.

13. Hill JC, Prasher DK, Luxon LM. Evidence efferent effects on auditory afferent activity and their functional relevance. Clin Otolaryngol. 1997;22:394-402.

14. Bruel MLF, Sanchez TG, Bento RF. Vias auditivas eferentes e seu papel no sistema auditivo. Arq Otorrinolaringol. 2001;5:62-7.

15. Guinan JJ. Olivocochlear efferents: anatomy, physiology, function, and the measurement of efferent effects in humans. Ear Hear. 2006;27:589-607.

16. Guinan JJ. Cochlear efferent innervation and function. Curr Opin Otolaryngol Head Neck Surg. 2010;18:447-53.

17. Sanches SGG, Carvallo RMM. Contralateral suppression of transient evoked otoacoustic emissions in children with auditory processing disorder. Audiol Neurootol. 2006;11:366-72.

18. De Boer J, Thornton ARD. Neural correlates of perceptual learning in the auditory brainstem: efferent activity predicts and reflects improvement at a speech-in-noise discrimination task. J Neurosci. 2008;28:4929-37.

19. Durante AS, Carvallo RMM. Contralateral suppression of linear and nonlinear transient evoked otoacoustic emissions in neonates at risk for hearing loss. J Commun Disord. 2008;41:70-83.

20. Matas CG, Silva FN, Leite RA, Samelli AG. Estudo do efeito de supressâo no potencial evocado auditivo de tronco encefálico. Pró-Fono. 2010;22:281-6.

21. Kumar A, Barman A. Effect of efferent-induced changes on acoustical reflex. Int J Audiol. 2002;41:144-7.

22. Amaral IEBR, Carvallo RMM. Limiarelatência do reflexoacústico sob efeito de estimulaçâo contralateral. Rev Soc Bras Fonoau-diol. 2008;13:1-6.

23. Oldfield RC. The assessment and analysis of handedness: The Edinburgh inventory. Neuropsychologia. 1971;9:97-113.

24. Vallejo LA, Hidalgo A, Lobo F, Tesorero MA, Gol-Carcedo E, Sánchez E, et al. ¿Es el oido medio el primer filtro de selección frecuencial? Acta Otorrinolaringol Esp. 2010;61:118-27.

25. Stach BA, Jerger JF, Jenkins HA. The human acoustic tensor tympani reflex: a case report. Scand Audiol. 1984;13:93-9.

26. Burnett PA, Miller JM, Mangham CA. Intra-aural reflexes elicited by a cochlear prosthesis in monkeys. Hear Res. 1984;16: 175-80.

27. Garinis AC, Glattke T, Cone BK. The MOC reflex during active listening to speech. J Speech Lang Hear Res. 2011;54: 1464-76.

28. Galambos R, Makeig S. Physiological studies of central masking in man: Part I—The effects of noise on the 40-Hz steady-state response. J Acoust Soc Am. 1992;92:2683-90.

29. Galambos R, Makeig S. Physiological studies of central masking in man: Part II—Tonepip SSRs and the masking level difference. J Acoust Soc Am. 1992;92:2691 -7.

30. Sab SK, Lang AH, Salmivalli AJ, Johansson Rk, Peltola MS. Contralateral white noise masking affects auditory N1 and P2 waves differently. Int J Psychophysiol. 2003;17:189-94.

31. Salisbury DF, Desantis MA, Shenton ME, McCarley RW. The effect of background noise on P300 to suprathreshold stimuli. Psy-chophysiology. 2002;39:111-5.

32. Weihing J, Musiek FE. An electrophysiological measure of binaural hearing noise. J Am Acad Audiol. 2008;19:481-95.

33. Simóes MB, Souza RR, Schochat E. Efeito de supressâo nas vias auditivas: Um estudo com os potenciais de média e longa latên-cia. Rev CEFAC. 2009;11:150-7.

34. Schochat E, Matas CG, Samelli AG, Carvallo RMM. From otoa-coustic emission to late auditory potentials P300: the inhibitory effect. Acta Neurobiol Exp. 2012;72:1-12.