hl II’ 1401 El\ev~er

HEARES

Thl\

B V

All

right\

Frequency

selectivity

stud)

III order

ha\

undertdhen

,cn\ltlvlty

the notched

spectral

Ioel

fIndIng\

Indlc,tte

ulth

Puhh\her\

reverved

037X-.iYS5,‘07/$05

\ubJectr

dnd the lo\\

noise method

in workers with noise-induced

to document,

01 trequency

Twelve

notch

that above d cert,~ln degree

In Io\r, ot +en\ltl\lty

In autlltnry

tdter

widths

h‘lndwldth

ot an lndlvldu.ll

Frequency

selecilvlty.

from

Bd\ed

hcdrlng

Nol$e-lnduccd

of hearing

were

\IY

tested,

lo\\.

which

seem\

ol hearing

on the datd

collected

lo\\.

AudItoo

tlltrl

343-5710

to

R

Hetu,

Groupe

MontrGdl.

d Acou\tlque

Qutbec

Canada

to he around 1, \lmdar thl\

study.

in

worker\

30 dB HL, orlgln

II 1’1 not

with

the rel,rtlon tllter

respect

havmg ddterent lrequency

\cItxtl\lty

and In m,tgnltude. po\s~hlr

thcrc

to cldequ,ltrly

hctwern

the 1~9

shapes were rjtlmatrd

to the \~gnal trequency. degrees tend\

01 hedrlng to decrca\e

I\ a lrlde prccl~ct

lo\\

varlatlon

the audlton.

the The

Ilncarly among hltcr

handuldth

People workmg m noisy envlronments often have to detect warning sounds m those environments. Thu 77

38 18 Yl 7x II) h Y7

0 0 0 II

YO Y-l 96 Yh

12 I7 1’)

I)

YJ

IX

I) 47

IX

77

II) .s

0 YJ

IX

Condltlon\

N

\

r

SEM

0 0, 0 7, 0 1. 0 3. 0 5. 0 5. 0 7.

‘2 ‘3 33 22

51 70 46 7x

0 YJ

12

IO 7

0 YX

77 72

Y1 147

0 YX 0 YY

I? 17 15 17 17 15 17

3

SEM

I5

hHz

00 0 2 04 05 07 I) 3 05

I) 97 u YX 0 Yf>

1s very broad, a few dB error can markedly change the filter shape. For this reason, the rehablhty of masked thresholds measured with the BCkCsy method was assessed. As stated in the Procedure section, the standard error of measurement was calculated. The equation used has the followmg form (Ferguson, 1972). Se.m

=sJ(l-r)

(4)

where S e.m IS the standard error of measurement. 5 corresponds to the standard devlatlon of the masked thresholds and r IS the correlation coefficient between the first and the second measurements series, that 15, the rellablhty coefficient According to this statistical formula. the expression \/(l - r) 1s a sampling estimate of the portion of scores variability that is attributable to the error of measurements. Since the error can be assumed to be independent of the magnitude of the audiometric score, S e m can be used as the standard error associated with a smgle score and interpreted m the same way as the standard error of any statlstlc. Depending on the frequency and the notch width, the analysis was done on 22 to 33 data points, always Including a mmlmum of 22 subjects. Table II presents the standard error of measurements at 1 and 3 kHz for each bandwidth value. The measurement error at 1 and 3 kHz was less than 2 dB, which compare5 well with the measurements errors calculated by HCtu (1979) for well controlled measurement condltlons in quiet. In that study, the measurement errors were 2 dB, 2 dB, 25 dB. 25 dB and 4 dB at 1, 2, 3. 4 and 6, kHz respectively. In a recent study (H&u and Tran Quoc, 1992). the notched-noise method of measurement was

hh

used wtth normal hearmg subjects and the measurement errors at 0 5, I and 3 kHz were 1.5 dB, 2 dB and 2 dB. respectively. A similar degree of rehabihty was

#4 Treshold

tound by Lutman et al (1001) In the mcasurcment ot auditory filter bandwidths usmg the notched-notsc procedure with an adaptative manual audrometry method.

64 - R - 3000 - 50

- R - 1000 - 50 ERB

(dB): 10

Treshold

(Hz): 131

ERB

(dB): 43

(Hz): 990

0

0 -10

-10

-20

Filter attenuation

Filter attenuation -30 (dB) -40

( dB)

-20 -30 -40

-50

-50

-60

-60

-70

-70 -0,6

-0.4

mO,2

O

0.2

O,4

0.6

!

!

!

!

!

-0.6

-0.4

-0,2

0

6.2

Treshold

I

0.~4

@,6

9

9

#1

I

#1

- R - 1000 - 50 ERB

(dB): 1

Treshold 0

(Hz): 179

0 -10

- R - 3000

(dB): 49

-

ERB

50 (Hz): 17 37

-10 -20

-20

Filter attenuation -30 (dB)

Filter at1lenuation -30 (dB) -40

++++++-I

-50

-50 -60 -70 -0.6

-0,4

-0,2

0

0,2

0,4

-0,6

0.6

-0,4

-0,2

9

(dB): 17

0,2

0.4

0.6

9

#5 - R - 1000 - 50 Treshold

0

ERB

#5 - R - 3000 - 50

(Hz): 169

Treshold

0

(dB): 48

ERB

(Hz): 2409

0

-10

-10

-20

-20

Filter attenuation -30 (dB) -40

Filter attenuation -30

(dB)

-40

-50 -60 -70 -0.6

-0.4

-0.2

0

0,2

0.4

0.6

-0,6

-0.4 -0,2

0

0.2

0,4

0,6

9 4 Fig2 Examples of audItory filter shapes for sublects Nos 4 (Right ear). 1 (Right ear)and 3 (Left ear) at loo0 and 3000 Hz. at a spectral level 01 50 dB/Hz

They obtamed test-retest correlatton coefficients m excess of 0 Y In summary, the typical error of measurement was about 3 dB This 1s probably shghtly greater than would be obtamcd with a forced-choice adaptive method However, the B&k&y method takes constderably less time Errors of 7 dB have only a small effect on the derived filter shape when the masked thresholds cover a reasonable range (> IO dB). However. when the masked thresholds cover only d small range such error\ can have d constderable effect When the range of masked thresholds IS less than 5 dB, the falter shape IS essentially indeterminate

When the threshold data were Inspected, four ears at 3 kHz (subjects No. 15-R. No. 17-R, No 18-L and No 20-R) were found to show less than a 5 dB dtfference m threshold between the zero notch condition dnd the 0.5 \ymmetrtc notch condition As described above, in wch cases, the dudltoIy falter shape cannot be dertved accurately, all that can be said 1s that the auditory filter was very broad at 3000 Hz, probably with a relative bandwidth (bandwtdth/centre frequency) of I or more In several cases, especially at 3 kHz, moving the upper noise band away from the signal frequency (I e. wtdenmg the notch) did not result m any reduction of threshold rclatlve to the corresponding symmetrlcnotch condtttons (0.3 0.3, 0.3 0.4, 0 5 0 5) In these cases the upper noise band must have been producing negligible masking compared with the lower band, thus. tt made no dtfferencc when the upper band was moved away Essentrally, when the lower skirt of the filter 1s much shallower than the upper skirt, the slope of the upper skirt IS not well determined by the data In practice, m such cases. the fitting program derives a very steep upper skirt (which makes the upper noise band contrtbute very little - it IS filtered out) Eight ears at 3 kHz (Nos 1-L. 3-L, 6-L, 6-R, Y-R, 13-R. 14-R, and 22-R) and two at 1 kHz (21-R and 23-R) gave filter shapes which had values of pu much greater than would be expected m a normal ear The data m these cases all showed no release from masking when the upper noise band was moved away A sharper-than-normal upper filter skirt would be a rather unlikely occurrence tn an Impaired ear. Neural tuning curves obtained from hearmg-impaired ears show that the upper skirt can be normal when the lower skirt IS flattened. but rt IS never steeper than normal (Evans, lY75) Hence, the data for these unusual cases were re-analyzed with the value of pu constrained to be less than or equal to 30 1 at 1000 Hz or 34.4 at 3000 Hz; these are the p values found for normal ears at these frequencies for a noise spectrum level of 50 dB (Glasberg and Moore. 1990)

I-ABLE

111

Auditory filter charactenstu (PI, Pu. ERB) tar the left car CL) md right ear (R) ot each whlect, at 1000H7. 50 dB/H7 A\tensked Pu vdue\ dre those which would he greater it not con\tralnrd Suhjcct number I-L 1-R 2-R 3-L I-R 5-R (>-L h-R 7-R 7-L H-R Y-R 0-L IO-R IO-L I I-L 12-R 13-R 13-L 14-R 15-R Ih-R 17-R IX-L IY-L I’)-R X-R 71-L ‘I-R 22-R ‘3-R

Threrholcl

PI

PU

ERR

(dB) h 0

I0 - I0 IY 0 IO 0 I7 0 IX 0 I8 0 17 0 2h (I 3 0 4 0 x 0 45 0 50 0 Y 0 13 0 IY 0 ‘72 0 7 0 ‘4 0

20 Y 1’) 5

0 17x

1’) 3 21 5 ‘5 3 2’ 6 I9 6 I74 I4 h

0 I75

Ii h 73 4 2.5 s 15 I I1 4 74 33 5 I7 Y I h fl IS s 1.3 t1

0 l7Y 0 IX7 0 131

0 IhY 0 IX5 0716 0 71 I 0 ?U 0 17’ 0 143 I) 13x 0 73x 0 14’) 0 I17 0 70.3 0717 0 71’) 0 I72 0 304 0 lb.3 0 Ihi 0 Ii5

0 0

II 4 2.1 h 7-l -3 _21 0 ‘I h

I 0

1’) Y

0 IS’

4 0

17 s

0 Ii3

I8 0

I7 0

0 1’)’

I1 0

I’)?

Y 0

2x Y

32 0

175

0 I70 0 104 0 730

-5

0 0 0

26 0

0 IhY

Fig. 2 presents examples of auditory filter shapes for different degrees of hearmg loss The correspondmg audiometrtc thresholds are tndtcated m the figure. together with values of the derived ERBs. Tables III and IV present the mdividual characteristics of the audrtory filters measured at 1 and 3 kHz for edch subject. The masked thresholds on which the audttoty falter characteristics are based are reproduced In Appendix (Tables Al and A2) The normal ERB value at 1 kHz for notched noise at 50 dB/Hz IS 155 Hz (Glasberg and Moore. 1YYO). The ERB values for the three subjects whose filters are shown m Fig 3 arc 131 Hz, 17Y Hz and 182 Hz Despite the fact that the filters for subjects Nos 1 and 3 have slmllar ERB values, their hearing thresholds differ stgnrftcantly. 1-c , 1 dB vs IY dB This variation ~111 be discussed In section C. The standard devtatmn of the ERBs for normally hearing subjects has been estimated to be about 108 of the mean ERB value (Moore, 19X7; Moore, Peters and Glasberg, lYY0; Peters and Moore, IYYZ’a,b). Thus, YSpG of the values would be expected to fall wtthm

I-ABLE

IL

Audrtory hltrr chardcteriatlcs (PI, Pu. ERB) for the lett e,,r CL) dnd right ear (R) of each subyxt. dt 3000 Hz. 50 dB/Hz A\terlskrd 1’11 value\ .ue those which would be gredler 11 not con\tr,uned SUbJeCt

Threshold

number

(dB)

I-R 2-R 3-L 3-R 4-R 5-R 6-L. 6-R 7-R 7-L H-R 9-L Y-R II-R 11-L 13-R 13-L 14-R 16-R IY-L 19-R 21-R 21-L ‘2-R

4’) 0 1’0 4s 0 18 0 33 0 18 0 57 u 59 0 44 0 s4 0 42 ll

16~0 11 0 7x (I 27 0 21 0 37 0 43 0 50 13 0 17 0 Jh 0 5YO 10 0

PI

7h 1.5 4 62 67 10s 4’ 2.6 11 0 96 56 6’ 11 6 13 1 176 134 10 8 7x 48 1s 7 13 5 13 4 24 75 16 3

Pu

r

discussed above. pu values ale otten dlttlcult to c\tlm mate and cdn tw misleddlng Hence. only the rclal~on bctwecn the degree of hcanng 1055 and the ERR u.111 be presented

11RB

0 233 0 57Y 0 176 0 376 0 XY9 0 32’) 0 x03 0 73Y 071-1 0 2x7 0 x23 0 147 0 773 0 310 0218 0 254 0 745 0 37.5 0 466 0 710 0 224 0 72x 0 901 OY51 0 IX1

+ / - 20% of the mean. At 1 kHz and 50 dB/Hz, this corresponds to a range from 124-186 Hz. Of the 31 ears in Table III, 20 are wlthm this range, while 11 have larger ERBs. At 3 kHz, the normal ERB value IS 425 Hz at 50 dB SPL/Hz (Glasberg and Moore, 1990), so 95% of normal values would be expected to fall in the range 340-510 Hz. The ERBs of the filters shown in Fig. 2 are 975 Hz, 1635 Hz and 2301 Hz All the ERB values at 3 kHz, as shown m Table IV, are outside the normal range, even those for subjects with near-normal absolute thresholds. Relatron between loss of sensltivgy and ERB In prinaple, several measures of frequency selectlvlty can be extracted from our data. Perhaps the slmplest is the threshold in the 0.0, 0.0 condltron, which IS related to the critical ratio. However, this measure showed essentially zero correlation with the absolute thresholds, m agreement with many other studies (Patterson et al., 1982, Glasberg and Moore, 1986; Lutman et al , 1991). This probably occurred because the crltical ratio confounds frequency selectwlty and processing efficiency (Patterson and Moore, 1986). Frrquency selectivity can also be measured m terms of the p values of the derived filter shapes. However, as

Data at I XH,Fig. 3 presents the ERBs plotted as a function ot absolute threshold at I kHz m dB HL The open circles represent cases where the v&e of pu was not constramed m the fitting procedure The asterisks reprcsent cases where the value of pu was constrained to be less than 30.1 There were only two casts where the hearmg loss was over 30 dB, which makes It difficult to estabhsh a clear relationship behveen absolute threshold and the ERB. For this reason, data from Glasberg and Moore (1986) have been added (solid circles). although these data refer to different etlologles of hearmg loss (M&&e’s, Alport’s syndrome, progressive and non-progressive cochlear loss, and noise-Induced loss). The combined results can be characterized by two hnear segments, a horizontal one dnd a slopmg one which Intersect around 30 dB HL. To find the best-fitting Intersection pomt (IP), the data were partltioned into two sets, below and above various values ot the IP (20-40 dB HL), and correlation coefficients were calculated for the regression Imes for the two sets of data On the low side of the IP, there was no sigmflcant change m the coefflclent with the value ot the lP, whereas on the high side, the coefficient was highest when the limit was set at 30 dB HL. The solid lmes are the best-fitting hnes obtamed m this way.

E

/ 0

-10

I

0

I

10

I

20 Threshold

I

30

I

40

I

50

I

60

70

(dB HLI

FIN. 3 The ERB al 1000 Hz plotted against the absolute threshold III Open circles show cases where the values of pu were not constrained (see text), asterisk where pu was constramed to be less than 30 I Fdled circles are data from Glasberg and Moore (1986) The sohd hnes are the best horizontal and slopmg fits tn the data.

dB HL at 1000 Hz

506 2

I

0

CF 0

* 0

O

8

E

* i

L-L

0 -10

0

10

20 Threshold

30

40

50

60

70

(dB HL)

ERB tar 50 dB SPL at NO(I

t lz

Based on this analysts, the ERB is almost constant for absolute thresholds up to 30 dB HL The data of Lutman et al (1991) show a slmllar trend. When the threshold exceeds 30 dB HL. the ERB tends to broaden The equation for the best-fitting slopmg line lb. ERB = - 0 075 + 0.0088 X (absolute

threshold)

C-5)

Although the overall trend of the data can be summarlzed by two straight lines. there IS a wide varlatmn m the ERBs at a given HTL This type of varlatlon has also been observed m other studies (Glasberg and Moore, 19X6; Lutman et al., 1091) If these results are to be used m a statistical detection model. It would seem appropriate to use the 95th percentile In order to predict detection values that WIII represent the majority of listeners This declslon IS crucial if one considers the need tor safety mvolved m the detection of warning sounds in noisy workplaces

Fig. 4 presents the relation between absolute thresholds and ERBs at 3 kHz. It was not possible to get a sensible two-line fit to these data due to the variability of the ERB especially for the higher thresholds Even so, by inspection the data can be separated Into a horizontal portion with a mean ERB of 0.23 below a threshold of 30 dB HL and an upwards sloping lme above this threshold value Upward-pointing arrows mdlcate cases where the range of thresholds was too

small to allow an ERB to be estimated, but where its value was probably 1 or more The dashed line mdicates the mean value of the ERB for normally hearing subjects at 3 kHz for a noise level of SO dB/Hz All of the ERBs are above this value. This suggests that prolonged noise exposure adversely affects frequency selectivity even when it has little or no effect on absolute threshold. A rclatcd effect for short-term noise exposure has been reported by Pick (I%O) He studled the recovery of hearing after a noise-Induced temporary threshold shift (TTS) Frequency \electlvity at 3 kHz was impaired up to about 30 day\ after the exposure, even though absolute thresholds returned to normal after about ten days When the absolute thresholds are above about 30 dB HL, the ERBs tend to increase substantially, although, as at 1 kHz. the spread in the data IS substantial. Part of the spread can be attributed to difficulties m determining the ERB accurately when its value IS large However. the overall spread 1s too large to bc accounted for m this way For example. for HLs bctween 55 and 60 dB, the range of ERBs IS from 0 37, to over 1 Despltc the wide variation ot the ERBs as a function of absolute threshold, these results do provide an emplrrcal basis for lmprovmg models intended to predict the audibility of warning signals m noisy work places It should be noted that the variability m the ERBs for subjects with high HTLs does not have very serious consequences for such models If the background sound IS noise with a relatively smooth spectrum, then the exact value of the ERB has only a small mtluence on predicted signal thresholds For example, predicted thresholds at a given signal frequency would increase by only 3 dB if the ERB were Increased from 0 5 to 1 ‘it that frequency The errors of prediction would, however. be more sermuc for noise\ with promlnent spectral peaks and dips.

Conclusions 0 The notched-noise method was used to collect information on frequency selectivity m noise-exposed workers The data indicate that above a certain degree of hearing loss (which seems to be around 30 dB HL). frequency selectivity tends to decrease at both 1 and 3 kHz. At 3 kHz, auditory filter bandwidths were conslderably greater than normal for subjects with absolute thresholds greater than 40 dB HL l Even when the degree of hearing loss 1s himlIar, there is a wide variation among SubJects m auditory filter bandwidth. In spite of choosing subjects with d similar cause for their hearing loss (in contrast to some earlier studies) we still only found a weak relationship between HTL and the ERB Thus the scatter m earlier

70

studres IS probably not a result of the varrety ot causes of hearing loss. Desptte thts vanation, the data can he used to Improve the audrtory detection model proposed by Laroche et al. (1991) l Based on the data collected m thts study, tt IS not possible to adequately predrct the ERB of an rndrvrdual from HTLs.

Acknowledgements This worh was supported by the lnstrtut clc Recherche en Sante et en SCcurnC du Travdrl L~LI Quebec. We would hkc to thank Brian Moore for many helpful suggestions and comments on an earlter version of thus paper

Appendix: Table Al and A2

TABLE

AI

Masked

thresholds

for the left ear (L) and right ear CR) ot each SubJect, at 1000 Hz, 50 dB/Hz.

for 12 notch width condltlons

SubJect number

Notch width condltron 00,oo

01,Ol

0.2, 0 2

03;03

0.4, 0 4

05.05

03.05

04,06

OS;07

05;03

0.6, 0 4

07.05

1 CL) 1 CR) 2 CR) 3 CL) 4 CR) 5 CR) 6 CL) 6 CR) 7 CL) 7 CR) 8 CR) 9 (L) 9 CR) 10 CR) 10 CL) 11 CL) 12 CR) 13 CL) 13 CR) 14 (R) 15 CR) 16 CR) 17 CR) 18 CL) 19 CL) 19 CR) 20 CR) 21 CL) 21 CR) 22 CR) 23 CR)

71 72 78 7’_ 72 72 71 73 76 X0 73 71 72 70 73 72 70 76 76 75 89 71 76 75 73 7.5 70 73 76 73 76

70 72 72 69 70 69 70 72 76 76 72 71 69 70 72 69 71 71 72 75 88 66 72 75 72 72 72 70 77 h8 73

60 67 72 60 62 61 67 66 70 71 63 62 60 63 65 57 64 67 66 67 81 60 68 63 63 67 60 65 66 5H 70

53 60 64 52 51 52 54 62 66 69 55 51 52 58 65 43 55 63 58 55 77 51 61 52 57 60 47 56 60 46 67

4.5 4Y 55 44 37 40 44 53 60 63 45 40 37 56 65 35 48 54 53 46 78 39 50 43 47 46 35 49 52 38 61

36 38 4.5 42 29 35 38 40 55 56 36 27 ‘7 58 60 26 41 48 45 38 74 30 36 39 35 41 32 40 40 35 55

50 58 58 46 50 47 52 60 61 66 47 49 48 60 63 36 53 55 55 48 73 47 55 4x 55 55 42 55 60 41 67

42 48 51 41 37 40 43 48 56 60 37 36 3.5 60 64 2h 44 52 51 44 70 35 46 43 42 46 31 48 51 34 61

30

41 46 48 44 33 42 43 47 58 57 42 32 34 56 62 3’) 46 51 .52 43 75 39 46 44 45 47 36 47 43 42 57

33 35 37 38 23 35 37 47 53 48 33 ‘7 27 58 5x 32 38 44 43 38 63 2x 32 36 34 37 31 37 34 38 50

26 30 31 36 27 33 32 41 47 42 30 21 23 56 57 30 30 36 36 32 61 23 26 37 23 30 76 33 30 33 45

37 39 37 28 34 36 43 52 52 32 26 23 58 60 21 39 46 45 31 67 26 33 36 34 38 23 41 40 27 56

71

TABLE

Al1

M,trhed

threshold\

SUhJKt

number

I (L)

1(R) 3(R) 3 (L) 3(R) J(R) 5 (R) h(L) h(R) 7 (L) 7 (R) K(R) Y(L) 0 (R) II(L) 11 (R) I3 (L) 13 (R) I-1(R) If> CR) IY (L) IY (R) 71 (L) 31 (R) 21 (R)

for the lett ear (L) and rght

ear (R) of each

suh~ecl.

.lt

3000

HL. SO JB/HL.

for I2 notch width condltlonr

Notch width condltlon 0 I). 0 0

70 70 7h 70 77 75 73 Xl x0 7h 74 70 7t> 7h 7.5 X0 53 X7 76 71 7h

76 s7 77 7h

II I. 0

71 75 7.3 77 7h OX 72

7x 70 77 17 78 74 71 75 x0 X0 7’) 7h VJ 7’) 76 XX 7h 76

I

0 2. 0 7 (10 7.1 68 77 75 f>fl 70 XI 76 71 7’ 7X 70 hY 71 77 x0 x0 75 hI 77 71. Xh 72 70

0 3. 0 3

04.04

0 5. 0 5

0 3. 0 5

0 1. 0 h

0 5, 0 7

0 5. 0 3

0 6. 0 4 -

hl 70 5X 73 71 60 67 77 72 71 hh 73 07 h’ ho ho 72 f>Y 74 4Y hX h4 x3 71 67

Sb hfl 47 hY 71 iY

hh

(13 117 55 73 71 (10 07 XII 7’ 72 67 77 5X hl 56 5h 71 71 73 JO hX hl X7 71 hI

57 hX 4X ho 6X h(l fl5 77 15 73 hl 70 i4 55

Sh

s3

h4

h’l

5s

-lb

(10

71 03

hh 711 ii

flf,

hh

73

7s

72

71

71 fl I 7h 72 0.7 h(> 7Y 71 71 71) 75 h5

Of,

73 73 71 65 71 hl 56 5fl 57 70 hX 71 37 hl 5fl x3 70 53

References

ANSI S3 I t IYXh) Amcrlcdn NatIonal Standard criteria tor permlh+ hle ,lmhlent IIOIW during audiometric testmg Am NJtl Stand In\t New York Bergman. M Najenson. T, Kern. C Hdrel. N. Erenthal. P and Sdchartov. E (1942) Frequency \electlvlty rls a potentId med\ure of nol\e damagr su\ceptlblllty Br J Audlol 76. 15 -27 Chung. D \r (IYHI) Tone-on-tone md\bmg In suhJect\ with normal hedrlng .Ind with \en\orlneur.d hearing loss. J Speech Hear Re\ 7-1. 506-5 I3 Coleman. G J Learnon. r B dnd Drayton. I D R (19X0) AudItory Communlatlon In the mlnlng mduatry. FInal Report on CEC Contract 62-15-l l/X/OlY/ Report No TM/XO/OI Coleman. G J Grdver. S G . Colher, S G , Goldmg, D . McNlcholl. A C; Slmpsrm. G C Sweatland K F dnd Talbot. c‘ F (IYKJ) Communtc.ltmns III nol\y rnvlronment\. Report TM X5 I In\t Qccup Med. Edinburgh. UK Evanx E F (lY75) The sharpening ot frequency \electlvlty In the normal ,lnd ,thnormal cochlea AudIolog) 14, JIY-442 FJulhnrr. A. Rosen. S and Moore B C J (1990) Residual frequency \eleLtlv!ty m the protoundly hedrmg-Impaired hjtenrr Br J Audlol 24 3Hlp3Y7 Ferguson, Ci A (1477) St.ltl\tlcal Andlysls m Psychology & Educdt~on McGraw-Hill. New Yorh. (3rd edn ) p 371 Fr\ten. J M and Plomp. R (19x3) Reldtlon\ between audItor) tunctlons 111lmpdlred hearmg J Acoust Sot Am 73. h52-h61 Florrntmr. M . Buus. S and Zwlcher. E (1980) Frequency selectlvlty In normally-hearing and ImpaIred-hedrmg observers, J Speech Hr.tr Ret 23, 646-669 Gl.lshcrg. B R . Moore. B C J and Nlmmo-Smith. 1 (19X4) Compdrl\on of .iudltory-filter Fhdpes derived with three different mashers J Acoust Sot Am 75. 536-544

h’l 65

-

67 77 74 72 51 70 OX x5 7.7 67

52 50 fiY (12 71 47 ho -5s x0 71 51

73

71

04

0I

72

07

0I

57

50

47

5X

50

5h

5’

70

;,;

hh

fl I

72

(17

41

79

(17

57

ot1

51)

X5

Xi

72

71

5h

n

0 7. 0 5

-

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