Acta Oto-Laryngologica
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Noise-Induced Hearing Loss and the Comprehension of Speech in Noise Sv. Quist-Hanssen, E. Thorud & G. Aasand To cite this article: Sv. Quist-Hanssen, E. Thorud & G. Aasand (1978) Noise-Induced Hearing Loss and the Comprehension of Speech in Noise, Acta Oto-Laryngologica, 86:sup360, 90-95, DOI: 10.3109/00016487809123483 To link to this article: http://dx.doi.org/10.3109/00016487809123483
Published online: 08 Jul 2009.
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Date: 28 April 2016, At: 16:39
Acta Otolaryngol, Suppl. 360: 90-95, 1979
NOISE-INDUCED HEARING LOSS AND THE COMPREHENSION OF SPEECH I N NOISE Sv. Quist-Hanssen, E. Thorud and G . Aasand From thr Instititte of Audiology. The Nrrtiontil Hospitcil of Nont.q. Oslo. Norit,tiy
of an individual ear on the basis of the hearing threshold for pure tones (Harris, 1965; examined by speech audiometry with a three-digit test. bisyllabic and monosyllabic PB word lists in silence. Meyers & Angermeier, 1972). One and the same loss for pure tones may result in differand in USASI noise with a masking effect of 44 dB and 68 dB at 1 kHz. Subjects with up to 20 dB hearing loss ing hearing loss for speech (Quist-Hanssen at 2 kHz had almost the same speech comprehension in noise as normal hearing subjects. Subjects with hear- & Steen, 1960). Hence it seems necessary to ing loss greater than 20 dB at 2 kHz had increasing dis- assess discrimination and hearing loss for crimination loss at increasing noise levels. They also speech directly by speech audiometry. needed a signal-to-noise ratio better than normal-hearIn Norway the evaluation of the hearing ing persons would yield at the noise levels used. The evaluation of hearing disablement in occupational noise- disablement is based almost exclusively on induced hearing loss should therefore be based for one- the results of pure tone and speech audiohalf on the results of speech audiometry in silence. and metry in a silent room. If there is a discriminafor the other half. in noise. tion loss the hearing loss for speech is corNoise-induced hearing loss (NIHL) affects rected through the hearing index table pubfirst and foremost the frequency area 4-6 lished by Frenckner et al. (1958). The perkHz, usually with a maximum at 4 kHz. As centage hearing disablement caused by asthe hearing loss worsens it spreads to lower sessed or corrected hearing loss for speech frequencies and even affects 2 kHz which is is given in tables of the National Insurance the frequency of greatest importance to speech System of Norway based on the computed comprehension. Even though the ability to binaural hearing loss for speech. To subjects with NIHL, this procedure perceive speech via the telephone or in faceto-face conversation may be well preserved, leads in the majority of cases to a very mild subjects with high-tone hearing loss have hearing disablement which does not reflect early on some difficulty in understanding the difficulties they experience when trying to speech in noisy conditions (Anianson, 1974; comprehend speech in noisy everyday conditions (Anianson, 1974; Klockhoff & Liden, Kuzniar, 1973). As the assessment of the hearing thresh- 1974). We therefore need an examination proold for pure tones is both simple and reliable, cedure better than speech audiometry in numerous methods have been proposed for silence which can predict the speech-hearing calculation of the hearing loss for speech in’ capacity of subjects with NIHL in everyday silent conditions (Alberti et al., 1976) and in noisy conditions. At the Institute of Audionoise (Pickett & Pollack, 1958) on the basis logy of the National Hospital of Norway a of the hearing loss for pure tones. It would background “USASI-noise” has been used. seem however, that there is no formula which Its electrical spectrum appears from Fig. 1. with satisfactory confidence can predict the The sound spectrum of 65 dI3SPL ordinary discrimination and hearing loss for speech room noise and its computed masking effect
Downloaded by [RMIT University Library] at 16:39 28 April 2016
Abstruct. Subjects suffering from noise-induced hearing loss (NIHL) with or without hearing loss at 2 kHz were
A c10 Otolar~tigolSitppl 360
Downloaded by [RMIT University Library] at 16:39 28 April 2016
Noise-induced hearing loss and speech comprehension in noise appears from Fig. 2 A. Fig. 2 B shows that the observed masking by 55 dBA USASI-noise conforms closely to the computed masking of 65 dBSPL room noise. For speech audiometry we used QuistHanssen’s word lists (1970) (a three-digit test, and PB lists of bisyllabic and of monosyllabic words) and USASI noise on tapes. Two noise levels were used, giving 62 dBSPL (58 dBA) and 82 dBSPL (78 &A) respectively in a 6 cc coupler. In normal-hearing subjects the noise levels produced 44 dJ3 and 68 dB hearing threshold level at 1 kHz and masking audiograms as shown in Fig. 3. The material consists of 20 subjects from 35 to 83 years of age, averaging 57 years, 2 women and I8 men. Sensorineural high-tone hearing loss was present in 36 ears, in 26 ears of characteristic NIHL type with better hearing at 8 kHz than at 3-6 kHz. Seven ears in which the hearing loss at 2 kHz did not exceed 20 dB are labelled NIHL I1 degree, 29 ears whose hearing loss exceeded 20 dB at 2 kHz are labelled NIHL 111 degree . I Eight normal ears in young adults served as controls. The mean hearing threshold level in the subjects with normal hearing, I1 or I l l degree NIHL appears from Fig. 4. The results from speech audiometry in silence and two levels of USASI noise are shown in Table I. The hearing threshold levels of the normal ears in silence are in agreement with previous findings. The common hearing threshold level for the digit test, the bisyllabic and monosyllabic PB word lists, is the intended result of the calibration of the speech audiometry material (Quist-Hanssen, 1970). In all three listening conditions, subjects with NIHL scored better in the digit test than in the bisyllabic and monosyllabic word tests. The difference is greater in silence than in noise, as in silence, subjects with NIHL benefit from their preserved hearing in the low and middle frequency areas for the understanding of the digits which, for statistical
91
II
IOHX
100
I IIMI FREOUEWCY
10
100 uw.2
Fig. I . Voltage spectra for three different masking noises.
reasons, require only a small amount of information. For the same reason, normalhearing subjects show a lower hearing threshold level for digits than for bisyllabic and monosyllabic words in noise. In USASI noise of 58 dBA the subjects with I1 degree NIHL need a signal-to-noise ratio (S/N ratio) from 0 t o 5 dB better, and those with 111 degree NIHL from 5 to 16 dB better than what normal hearing subjects require. In USASI noise of 78 dBA, subjects with I1 degree NIHL need a S/N ratio which does not differ from that of normal-hearing subjects, while those with I11 degree NIHL need an S/N ratio 6-11 dB better, as shown in Table 11. Although the need for a better S/N ratio decreases with increasing SPL of the noise, increasing discrimination loss (which appears from Table 111) reduces the comprehension
’ The following grading of NIHL is used: 0 degree: hearing loss not exceeding 20 dB at 2-6 kHz: I degree: hearing loss not exceeding 40 dB at 3.4 or 6 kHz; I1 degree: hearing loss exceeding 40 dB at 3.4 or 6 kHz: 111 degree: as I1 but with additional hearing loss exceeding 20 dB at 2 kHz.
Sv. Quist-Hnnssen et nl.
92
dl!
60
40
Downloaded by [RMIT University Library] at 16:39 28 April 2016
2c
0
-2(
Fig. 2 A . Sound spectrum and computed masking from 65 dBSPL ordinary room noise.
of speech. For satisfactory speech perception, subjects with NIHL must get the S/N ratio they need. Which S/N ratio will normal-hearing speakers offer the listener in a background noise? In investigations (by G. Flottorp, Sv. QuistHanssen and A. Sundby) speaker and listener sat 2.5 m apart in the USASI noise in a non-
reverberant room. The speaker spoke short sentences which the listener should understand and repeat. As in an everyday face-toface conversation the speaker could check that he was understood. Lip-reading was not used. The results are given in Fig. 5 which shows that the S/N ratio decreases with increasing SPL of the noise, as previously dem-
gb m L
=
1M
. I
Fig. 2 B . Computed masking from 65 dBSPL ordinary room noise - and observed masking from 55 dBA USASI noise . . .
Fig. 3. Masking audiogram from USASI noise of 62 dBSPL (58 dBA) and 82 dBSPL (78 DBA). Mean hearing threshold level and standard deviation for pure tones in 8 normal ears.
Noise-induced hearing loss and speech comprehension in noise
93
SIGNAL/NOISE
85/70
125
250
mo
lo00
ZOO0
4wo
8ooo
92/80
0
10
Downloaded by [RMIT University Library] at 16:39 28 April 2016
40
-2
:: -8
1 +
NOISE
AT LISTENER’S
1
EAR
Fig. 5 . Signal-to-noise ratios obtained by using sentences in USASI noise, 2.5 m distance between speaker and listener and no lip-reading.
0
10
60
Fig. 4 . Mean hearing threshold level for pure tones in:
( A ) normal ears (no. 8); ( B ) noise induced hearing loss I 1 degree (no. 7); ( C ) noise induced hearing loss 111 degree
(no. 29).
onstrated by Kryter (1965) and Picket & Pollack (1958). Already at 60 B S P L USASI noise the mean S/N ratio is reduced to 4 dB at the listener’s ear and at 65-70 dBSPL to 0 dB. At -1 dB S/N ratio the normally hearing subjects perceived all the sentences and at -4 dl3, 80% of them, thus agreeing with observations of Flanagan (1965) and Pickett ( 1956). However, large individual differences
Table 1. Mean speech reception threshold level d B re 20 @a in silence and in noise for subjects with normal hearing and II and III degree N I H L Di. = digits, Bi. = bisyllabic. Mo. = monosyllabic words Silence
58 dBA USASI noise
NIHL
Di.
0 I1 111
3 2 f 5 3322 372 5 4424 46210 5 7 2 9
Bi.
78 dBA USASI noise
Mo.
Di.
Bi.
Mo.
Di.
Bi.
Mo.
342 3 45+ 7 66+11
6742 67+4 72+5
72+3 71F4 81f7
7023 75+4 86+8
86+2 84+3 92f5
93?3 93f7 99f5
90+2 94+3 101f7
N
8 7 29
Acto Ololuryngol Sirppl -160
94
Sv. Quist-Hanssen et al.
Table 11. Difference in d B between speech reception threshold level in srrbjects Ic9ith riortnrrl hearing, II und III degree N I H L in silence and in USASI noise Di. = digits, Bi. = bisyllaabic, Mo. = monosyllabic words Silence
Downloaded by [RMIT University Library] at 16:39 28 April 2016
NIHL
Di .
58 dBA USASI noise Bi .
Mo.
Di .
Bi .
Mo.
78 dBA USASI noise Di .
Bi.
Mo.
are observed in the speech SPL given by different speakers in the same noise (Pickett, 1956). In noise up to 85 dBA one should, however, expect normal-hearing subjects to yield a S/N ratio at least 5 dB above the critical ratio for normal-hearing subjects, and in many cases even 10 dE3, though decreasing with increasing SPL of the noise (Kryter, 1965). Table I1 shows that subjects with I1 degree NIHL at both the USASI noise levels used may expect a signal-to-noise ratio which permits them to comprehend speech. For the majority of the subjects with 111 degree NIHL the S/N ratio presented will not be satisfactory and will hinder or prevent speech perception. At SPL above 78 dB the intelligibility of speech in noise is not only reduced, but is so to an increasing extent with increasing SPL, despite a constant S/N ratio (Pickett & Pollack, 1958). Even if the actual S/N ratio were to satisfy the needs of the hearingimpaired for speech comprehension, the increasing SPL of the noise would cause an increasing discrimination loss and thereby reduce speech perception (see Table 111).
Subjects with high-tone hearing loss benefit from lip-reading in noise just as much as in silence (Klockhoff & Liden, 1974). The ability to lipread varies from person to person and the benefit obtained depends on good sight and good lighting. Lip-reading should therefore not be taken into account in the evaluation of hearing disablement. The advantage of binaural (dichotic) hearing in everyday life is fairly uniformally evaluated (Lierle, 1961; Alberti et al., 1976), I/5 for the bad ear and 4/5 for the good ear may be a reasonable suggestion. Scarcely one-half of the speech we comprehend is presented to us clearly and under favourable listening conditions (Harris, 1965). With NIHL, the hearing loss for speech assessed by speech audiometry in silence should count for no more than one-half of the hearing disablement. The other half should be based on the result of speech audiometry against a background noise representative of everyday noise (such as USASI) of about 58 dl3SPL and the required S/N ratio and discrimination capacity must be decisive factors. The results of these examinations should however be compared with the hard-of-hearTable 111. Percertrage discrimination ioss ( P B ing person’s own appraisal of his hearing, as monosyllabic words) in silence and in noise in emerges from interview according to standsubjects Kith II and 111 degree noise-induced ardized questionnaire. hearing loss
NIHL 11
I11
Silence
o+ 0 9k13
58 dBA USASI noise 4.3f I 1 13.3flS
78 dBA USASI noise
REFERENCES
10 ? I S 28.1f24
Alberti, P. W., Morgan, P. P., Fria, T. J . & LeBlanc, J . C . 1976. Percentage hearing less. Various schema applied to a large population with noise-induced hearing loss. In Eff’rcts of Noise on Hearing (ed.
Downloaded by [RMIT University Library] at 16:39 28 April 2016
Noise-induced hearing loss and speech comprehension in noise R . P. Hamernik, D. S. Dosanjh & J. H. Miles), p. 479. Raven Press. New York. Anianson, G . 1974. Methods for assessing high frequency hearing loss in every-day listening conditions. Actu Otoluryngol (Stockh), Suppl. 320. Flanagan. J . L . 1965. Speech Ancr/ysi.s, Svnthesis c r n d Prrcc>ption,pp. 234, 240, 270. Springer-Verlag. Frenckner, P., Liden, G.. Engstrom, M . & Uggla, J . 1958. H6rsc~linvuliditet~ninorn v r X e s s b a d e , f ~ ~ r s ~ i k ringen. Almqvist & Wiksell. Stockholm. Harris, J . D. 1965. Pure tone acuity and the intelligibility of every-day speech. J Acoust Soc Am 37, 824. Klockhoff, I . & Liden, G. 1974. De bullerskadades horselinvaliditet och yrkessakdeforsakringen. Liikurtidningen 71, 819. Kryter, K . D. 1965. On predicting the intelligibility of speech from acoustic measures. J Speech H e w Dis 21, 208. Kuzniar, J . J. 1973. Hearing loss and speech intelligibility in noise. In Proc. Congr. Noise us ( I Public Heulth Problem, Dubrovnik. p. 57. Lierle, D. M . 1959. Guide for the evaluation of hearing impairment. Trans Atn A c Ophthalm Otol63, 236. - 1961. J A M A 177. 492.
95
Meyers, C . K . & Angermeier, C. 1972. Hearing loss at 3 kiloHertz and the CHABA "Proposed clinical test of speech discrimination in noise". U.S.A. Nuv. Subniur. M e d . Res. Lab. Report 720. Pickett, J. M . 1956. Effect of vocal force on the intelligibility of speech sounds. J A~~orr.st Soc A m 28. 902. Pickett, J . M . & Pollack, J . 19%. Prediction of speech intelligibility at high noise levels. J Acoust Sot, Am 30, 955
I
Quist-Hanssen, S. 1970. I n Rojskjzr. C . , SpcJech Audiometry. Second Danuvor Svmposiuni. Odense, pp. 227229. 256. Quist-Hanssen & Steen, E. 1960. Observed and calculated hearing loss for speech in noise-induced deafness. Acrn Otolnryngol (Stockh), Suppl. 158. p. 277.
Sv.Quist-Hunssen Institute of' Audiology The Nationul Hospital Oslo Norwwy
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Noise-Induced Hearing Loss and the Comprehension of Speech in Noise Sv. Quist-Hanssen, E. Thorud & G. Aasand To cite this article: Sv. Quist-Hanssen, E. Thorud & G. Aasand (1978) Noise-Induced Hearing Loss and the Comprehension of Speech in Noise, Acta Oto-Laryngologica, 86:sup360, 90-95, DOI: 10.3109/00016487809123483 To link to this article: http://dx.doi.org/10.3109/00016487809123483
Published online: 08 Jul 2009.
Submit your article to this journal
Article views: 29
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ioto20 Download by: [RMIT University Library]
Date: 28 April 2016, At: 16:39
Acta Otolaryngol, Suppl. 360: 90-95, 1979
NOISE-INDUCED HEARING LOSS AND THE COMPREHENSION OF SPEECH I N NOISE Sv. Quist-Hanssen, E. Thorud and G . Aasand From thr Instititte of Audiology. The Nrrtiontil Hospitcil of Nont.q. Oslo. Norit,tiy
of an individual ear on the basis of the hearing threshold for pure tones (Harris, 1965; examined by speech audiometry with a three-digit test. bisyllabic and monosyllabic PB word lists in silence. Meyers & Angermeier, 1972). One and the same loss for pure tones may result in differand in USASI noise with a masking effect of 44 dB and 68 dB at 1 kHz. Subjects with up to 20 dB hearing loss ing hearing loss for speech (Quist-Hanssen at 2 kHz had almost the same speech comprehension in noise as normal hearing subjects. Subjects with hear- & Steen, 1960). Hence it seems necessary to ing loss greater than 20 dB at 2 kHz had increasing dis- assess discrimination and hearing loss for crimination loss at increasing noise levels. They also speech directly by speech audiometry. needed a signal-to-noise ratio better than normal-hearIn Norway the evaluation of the hearing ing persons would yield at the noise levels used. The evaluation of hearing disablement in occupational noise- disablement is based almost exclusively on induced hearing loss should therefore be based for one- the results of pure tone and speech audiohalf on the results of speech audiometry in silence. and metry in a silent room. If there is a discriminafor the other half. in noise. tion loss the hearing loss for speech is corNoise-induced hearing loss (NIHL) affects rected through the hearing index table pubfirst and foremost the frequency area 4-6 lished by Frenckner et al. (1958). The perkHz, usually with a maximum at 4 kHz. As centage hearing disablement caused by asthe hearing loss worsens it spreads to lower sessed or corrected hearing loss for speech frequencies and even affects 2 kHz which is is given in tables of the National Insurance the frequency of greatest importance to speech System of Norway based on the computed comprehension. Even though the ability to binaural hearing loss for speech. To subjects with NIHL, this procedure perceive speech via the telephone or in faceto-face conversation may be well preserved, leads in the majority of cases to a very mild subjects with high-tone hearing loss have hearing disablement which does not reflect early on some difficulty in understanding the difficulties they experience when trying to speech in noisy conditions (Anianson, 1974; comprehend speech in noisy everyday conditions (Anianson, 1974; Klockhoff & Liden, Kuzniar, 1973). As the assessment of the hearing thresh- 1974). We therefore need an examination proold for pure tones is both simple and reliable, cedure better than speech audiometry in numerous methods have been proposed for silence which can predict the speech-hearing calculation of the hearing loss for speech in’ capacity of subjects with NIHL in everyday silent conditions (Alberti et al., 1976) and in noisy conditions. At the Institute of Audionoise (Pickett & Pollack, 1958) on the basis logy of the National Hospital of Norway a of the hearing loss for pure tones. It would background “USASI-noise” has been used. seem however, that there is no formula which Its electrical spectrum appears from Fig. 1. with satisfactory confidence can predict the The sound spectrum of 65 dI3SPL ordinary discrimination and hearing loss for speech room noise and its computed masking effect
Downloaded by [RMIT University Library] at 16:39 28 April 2016
Abstruct. Subjects suffering from noise-induced hearing loss (NIHL) with or without hearing loss at 2 kHz were
A c10 Otolar~tigolSitppl 360
Downloaded by [RMIT University Library] at 16:39 28 April 2016
Noise-induced hearing loss and speech comprehension in noise appears from Fig. 2 A. Fig. 2 B shows that the observed masking by 55 dBA USASI-noise conforms closely to the computed masking of 65 dBSPL room noise. For speech audiometry we used QuistHanssen’s word lists (1970) (a three-digit test, and PB lists of bisyllabic and of monosyllabic words) and USASI noise on tapes. Two noise levels were used, giving 62 dBSPL (58 dBA) and 82 dBSPL (78 &A) respectively in a 6 cc coupler. In normal-hearing subjects the noise levels produced 44 dJ3 and 68 dB hearing threshold level at 1 kHz and masking audiograms as shown in Fig. 3. The material consists of 20 subjects from 35 to 83 years of age, averaging 57 years, 2 women and I8 men. Sensorineural high-tone hearing loss was present in 36 ears, in 26 ears of characteristic NIHL type with better hearing at 8 kHz than at 3-6 kHz. Seven ears in which the hearing loss at 2 kHz did not exceed 20 dB are labelled NIHL I1 degree, 29 ears whose hearing loss exceeded 20 dB at 2 kHz are labelled NIHL 111 degree . I Eight normal ears in young adults served as controls. The mean hearing threshold level in the subjects with normal hearing, I1 or I l l degree NIHL appears from Fig. 4. The results from speech audiometry in silence and two levels of USASI noise are shown in Table I. The hearing threshold levels of the normal ears in silence are in agreement with previous findings. The common hearing threshold level for the digit test, the bisyllabic and monosyllabic PB word lists, is the intended result of the calibration of the speech audiometry material (Quist-Hanssen, 1970). In all three listening conditions, subjects with NIHL scored better in the digit test than in the bisyllabic and monosyllabic word tests. The difference is greater in silence than in noise, as in silence, subjects with NIHL benefit from their preserved hearing in the low and middle frequency areas for the understanding of the digits which, for statistical
91
II
IOHX
100
I IIMI FREOUEWCY
10
100 uw.2
Fig. I . Voltage spectra for three different masking noises.
reasons, require only a small amount of information. For the same reason, normalhearing subjects show a lower hearing threshold level for digits than for bisyllabic and monosyllabic words in noise. In USASI noise of 58 dBA the subjects with I1 degree NIHL need a signal-to-noise ratio (S/N ratio) from 0 t o 5 dB better, and those with 111 degree NIHL from 5 to 16 dB better than what normal hearing subjects require. In USASI noise of 78 dBA, subjects with I1 degree NIHL need a S/N ratio which does not differ from that of normal-hearing subjects, while those with I11 degree NIHL need an S/N ratio 6-11 dB better, as shown in Table 11. Although the need for a better S/N ratio decreases with increasing SPL of the noise, increasing discrimination loss (which appears from Table 111) reduces the comprehension
’ The following grading of NIHL is used: 0 degree: hearing loss not exceeding 20 dB at 2-6 kHz: I degree: hearing loss not exceeding 40 dB at 3.4 or 6 kHz; I1 degree: hearing loss exceeding 40 dB at 3.4 or 6 kHz: 111 degree: as I1 but with additional hearing loss exceeding 20 dB at 2 kHz.
Sv. Quist-Hnnssen et nl.
92
dl!
60
40
Downloaded by [RMIT University Library] at 16:39 28 April 2016
2c
0
-2(
Fig. 2 A . Sound spectrum and computed masking from 65 dBSPL ordinary room noise.
of speech. For satisfactory speech perception, subjects with NIHL must get the S/N ratio they need. Which S/N ratio will normal-hearing speakers offer the listener in a background noise? In investigations (by G. Flottorp, Sv. QuistHanssen and A. Sundby) speaker and listener sat 2.5 m apart in the USASI noise in a non-
reverberant room. The speaker spoke short sentences which the listener should understand and repeat. As in an everyday face-toface conversation the speaker could check that he was understood. Lip-reading was not used. The results are given in Fig. 5 which shows that the S/N ratio decreases with increasing SPL of the noise, as previously dem-
gb m L
=
1M
. I
Fig. 2 B . Computed masking from 65 dBSPL ordinary room noise - and observed masking from 55 dBA USASI noise . . .
Fig. 3. Masking audiogram from USASI noise of 62 dBSPL (58 dBA) and 82 dBSPL (78 DBA). Mean hearing threshold level and standard deviation for pure tones in 8 normal ears.
Noise-induced hearing loss and speech comprehension in noise
93
SIGNAL/NOISE
85/70
125
250
mo
lo00
ZOO0
4wo
8ooo
92/80
0
10
Downloaded by [RMIT University Library] at 16:39 28 April 2016
40
-2
:: -8
1 +
NOISE
AT LISTENER’S
1
EAR
Fig. 5 . Signal-to-noise ratios obtained by using sentences in USASI noise, 2.5 m distance between speaker and listener and no lip-reading.
0
10
60
Fig. 4 . Mean hearing threshold level for pure tones in:
( A ) normal ears (no. 8); ( B ) noise induced hearing loss I 1 degree (no. 7); ( C ) noise induced hearing loss 111 degree
(no. 29).
onstrated by Kryter (1965) and Picket & Pollack (1958). Already at 60 B S P L USASI noise the mean S/N ratio is reduced to 4 dB at the listener’s ear and at 65-70 dBSPL to 0 dB. At -1 dB S/N ratio the normally hearing subjects perceived all the sentences and at -4 dl3, 80% of them, thus agreeing with observations of Flanagan (1965) and Pickett ( 1956). However, large individual differences
Table 1. Mean speech reception threshold level d B re 20 @a in silence and in noise for subjects with normal hearing and II and III degree N I H L Di. = digits, Bi. = bisyllabic. Mo. = monosyllabic words Silence
58 dBA USASI noise
NIHL
Di.
0 I1 111
3 2 f 5 3322 372 5 4424 46210 5 7 2 9
Bi.
78 dBA USASI noise
Mo.
Di.
Bi.
Mo.
Di.
Bi.
Mo.
342 3 45+ 7 66+11
6742 67+4 72+5
72+3 71F4 81f7
7023 75+4 86+8
86+2 84+3 92f5
93?3 93f7 99f5
90+2 94+3 101f7
N
8 7 29
Acto Ololuryngol Sirppl -160
94
Sv. Quist-Hanssen et al.
Table 11. Difference in d B between speech reception threshold level in srrbjects Ic9ith riortnrrl hearing, II und III degree N I H L in silence and in USASI noise Di. = digits, Bi. = bisyllaabic, Mo. = monosyllabic words Silence
Downloaded by [RMIT University Library] at 16:39 28 April 2016
NIHL
Di .
58 dBA USASI noise Bi .
Mo.
Di .
Bi .
Mo.
78 dBA USASI noise Di .
Bi.
Mo.
are observed in the speech SPL given by different speakers in the same noise (Pickett, 1956). In noise up to 85 dBA one should, however, expect normal-hearing subjects to yield a S/N ratio at least 5 dB above the critical ratio for normal-hearing subjects, and in many cases even 10 dE3, though decreasing with increasing SPL of the noise (Kryter, 1965). Table I1 shows that subjects with I1 degree NIHL at both the USASI noise levels used may expect a signal-to-noise ratio which permits them to comprehend speech. For the majority of the subjects with 111 degree NIHL the S/N ratio presented will not be satisfactory and will hinder or prevent speech perception. At SPL above 78 dB the intelligibility of speech in noise is not only reduced, but is so to an increasing extent with increasing SPL, despite a constant S/N ratio (Pickett & Pollack, 1958). Even if the actual S/N ratio were to satisfy the needs of the hearingimpaired for speech comprehension, the increasing SPL of the noise would cause an increasing discrimination loss and thereby reduce speech perception (see Table 111).
Subjects with high-tone hearing loss benefit from lip-reading in noise just as much as in silence (Klockhoff & Liden, 1974). The ability to lipread varies from person to person and the benefit obtained depends on good sight and good lighting. Lip-reading should therefore not be taken into account in the evaluation of hearing disablement. The advantage of binaural (dichotic) hearing in everyday life is fairly uniformally evaluated (Lierle, 1961; Alberti et al., 1976), I/5 for the bad ear and 4/5 for the good ear may be a reasonable suggestion. Scarcely one-half of the speech we comprehend is presented to us clearly and under favourable listening conditions (Harris, 1965). With NIHL, the hearing loss for speech assessed by speech audiometry in silence should count for no more than one-half of the hearing disablement. The other half should be based on the result of speech audiometry against a background noise representative of everyday noise (such as USASI) of about 58 dl3SPL and the required S/N ratio and discrimination capacity must be decisive factors. The results of these examinations should however be compared with the hard-of-hearTable 111. Percertrage discrimination ioss ( P B ing person’s own appraisal of his hearing, as monosyllabic words) in silence and in noise in emerges from interview according to standsubjects Kith II and 111 degree noise-induced ardized questionnaire. hearing loss
NIHL 11
I11
Silence
o+ 0 9k13
58 dBA USASI noise 4.3f I 1 13.3flS
78 dBA USASI noise
REFERENCES
10 ? I S 28.1f24
Alberti, P. W., Morgan, P. P., Fria, T. J . & LeBlanc, J . C . 1976. Percentage hearing less. Various schema applied to a large population with noise-induced hearing loss. In Eff’rcts of Noise on Hearing (ed.
Downloaded by [RMIT University Library] at 16:39 28 April 2016
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Sv.Quist-Hunssen Institute of' Audiology The Nationul Hospital Oslo Norwwy
