2. Puretone Audiometry:
Bone Conduction
• a conservative estimate of IA for bone conducted sound is 0 dB.
• Theoretically, masked bone conduction measurements are always required if ear-specific
information is needed.
• bone-conduction thresholds are primarily useful for determining gross site of lesion (i.e.,
conductive, sensory/neural, or mixed).
• The presence of air-bone gaps suggests a conductive component to a hearing loss.
• The major factor to consider when making a decision about the need for contralateral
masking during bone conduction audiometry is whether the unmasked bone conduction
threshold (Unmasked BC) suggests the presence of a significant conductive component in the
test ear.
3. Puretone Audiometry:
Bone Conduction
• The use of contralateral masking is indicated whenever the results of unmasked bone-
conduction audiometry suggest the presence of an air-bone gap in the test ear (Air-Bone Gap
Test Ear) of 15 dB or greater:
Air-Bone Gap Test Ear dB ≥ 15
Air-Bone Gap AC Test Ear - Unmasked BC
5. Puretone Audiometry:
Bone Conduction
contralateral masking will be required when
measuring bone-conduction thresholds in
both ears.
Comparison of unmasked bone conduction
thresholds to the air-conduction thresholds
suggests potential air-bone gaps ranging
from 30 to 35 dB in each ear.
6. Speech Audiometry
There are three factors to consider when making a decision about the need for contralateral
masking during speech audiometry:
• (1) IA
• (2) presentation level of the speech signal (in dB HL) in the test ear
• (3) bone-conduction hearing sensitivity (i.e.,threshold) in the nontest ear
Contralateral masking is indicated during speech audiometry whenever the presentation level of
the speech signal (in dB HL) in the test ear (Presentation Level Test Ear) equals or exceeds the best
puretone bone-conduction threshold in the nontest ear (Best BC Nontest Ear) by a conservative
estimate of IA:
Presentation Level Test Ear −Best BC Nontest Ear ≥ IA
7. Speech Audiometry
In the left ear:
Presentation Level Test Ear – Best BC Nontest Ear ≥ IA
20 dB HL – 55 dB HL ≥ 40 dB? No
In the right ear:
Presentation Level Test Ear – Best BC Nontest Ear ≥ IA
80 dB HL – 15 dB HL ≥ 40 dB? Yes
8. Speech Audiometry
a decision about the need for contralateral masking during measurement of speech thresholds can
be often made by comparing speech thresholds in the two ears.
Contralateral masking is required during measurement of speech threshold when the speech
threshold in the test ear (ST Test Ear) equals or exceeds the speech threshold in the nontest ear (ST
Nontest Ear) by a conservative estimate of IA:
ST Test Ear − ST Nontest Ear ≥ IA
9. Speech Audiometry
ST Test Ear – ST Nontest Ear ≥ IA
80 dB HL – 20 dB HL ≥ 40 dB? Yes
unmasked SRTs were measured at 65 and 20 dB HL
in the right and left ears.
Presentation Level Test Ear – Best BC Nontest Ear ≥ IA
65 dB HL – 15 dB HL ≥ 40 dB? Yes
10. Speech Audiometry
The need for contralateral masking during assessment
of suprathreshold speech recognition.
SRTs were measured at 0 dB HL in both ears.
Contralateral masking was not required during puretone
and speech threshold audiometry.
presentation level for both ears will be 50 dB HL
11. Speech Audiometry
supra-aural earphones are being used during speech audiometry
Presentation Level Test Ear – Best BC Nontest Ear ≥ IA
Right Ear 50 dB HL – 0 dB HL ≥ 40 dB? Yes
Left Ear 50 dB HL – 0 dB HL ≥ 40 dB? Yes
3A insert earphones are being used during speech audiometry:
Presentation Level Test Ear – Best BC Nontest Ear ≥ IA
Right Ear 50 dB HL – 0 dB HL ≥ 60 dB? No
Left Ear 50 dB HL – 0 dB HL ≥ 60 dB? No
12. Speech Audiometry
Two important concepts related to assessment of suprathreshold speech recognition.
First:
• it should not be assumed that contralateral masking is never required when assessing
individuals with symmetrical sensory/neural hearing loss.
Second:
• the need for contralateral masking often can be eliminated by using an air-conduction
transducer that provides greater IA (i.e., 3A insert earphone).
13. Masking Noise Selection
three types of masking stimuli:
• narrowband noise
• speech spectrum noise
• white noise.
Our clinical goal is to select a masker that is efficient.
• An efficient masker is one that produces a given effective level of masking with the least
overall sound pressure level.
14. Masking Noise Selection
White noise
White noise is a broadband stimulus that contains equal energy across a broad range of
frequencies.
• Because of its broadband spectrum, it has the ability to mask puretone stimuli across a broad range
of frequencies.
• “critical bandwidth,”
• This concept of the critical band as first described by Fletcher (1940) consists of two components:
1. When masking a puretone with broadband noise, the only components of the noise that have a
masking effect on the tone are those frequencies included within a narrow band centered around
the frequency of the tone.
• selecting an appropriate masker during puretone audiometry
2. When a puretone is just audible in the presence of the noise, the total noise power present in the
narrow band of frequencies is equal to the power of the tone.
• calibrating the effective masking (EM) level of the masking stimulus.
15. Masking Noise Selection
White noise is adequate as a masker for Puretone stimuli.
• However:
• it contains noise components that do not contribute to the effectiveness of the masker.
• The additional noise components outside the tone’s critical band simply add to the overall level
(and loudness) of the masking stimulus.
• narrow band noise
o the most efficient masker for Puretone stimuli is a narrow band of noise with a bandwidth slightly
greater than the critical band surrounding the tone.
o It provides the greatest masking effect with the least overall intensity.
To minimize the perception of tonality that often is associated with very narrow bands of noise, the
bands specified by ANSI/ASA are somewhat wider than the critical bands for EM.
• The goal is to avoid confusion of the masker with the signal.
16. Masking Noise Selection
Speech spectrum noise is typically used as a masker during speech audiometry.
Speech is a broadband stimulus that requires a broadband masker.
The average spectrum of speech contains the greatest energy in the low frequencies with spectrum
level decreasing as a function of increasing frequency
• a sound pressure spectrum level that is constant from 100 to 1,000 Hz, decreasing at a rate of 12
dB per octave from 1,000 to 6,000 Hz.
Speech spectrum noise is white noise that has been filtered to simulate the long-
term average spectrum of speech.
17. Calibration of Effective Masking Level
EM level for puretones
• the sound pressure level of a band of noise whose geometric center frequency coincides with
that of a specific pure tone that masks the pure tone to 50% probability of detection”
in individuals with normal hearing:
• “the amount of effective masking is equal to the number of decibels that a given band of
noise shifts a pure-tone threshold;
• when the band of noise and the pure tone are presented simultaneously to the same ear”
18. Calibration of Effective Masking Level
• effective masking (in dB EM) refers to:
The HL (dB HL) to which puretone threshold is shifted by a given level of noise; and
The puretone threshold shift (in dB) relative to 0 dB HL provided by a given level of noise.
19. Calibration of Effective Masking Level
Example 1:
A puretone air-conduction threshold is measured at 0 dB HL in the right ear.
A narrowband noise geometrically centered at the test frequency is presented to the same ear
at 50 dB EM.
• This EM level of 50 dB will shift puretone threshold to 50 dB HL.
effective masking (in dB EM) refers to:
The HL (dB HL) to which puretone threshold is shifted by a given level of noise
20. Calibration of Effective Masking Level
Example 2:
A puretone air-conduction threshold is measured at 30 dB HL in the right ear.
A narrowband noise geometrically centered at the test frequency is presented to the same ear
at 50 dB EM.
• This EM level of 50 dB will shift puretone threshold to 50 dB HL.
• effective masking (in dB EM) refers to:
The HL (dB HL) to which puretone threshold is shifted by a given level of noise; and
The puretone threshold shift (in dB) relative to 0 dB HL provided by a given level of noise.
22. Calibration of Effective Masking Level
• EM for speech refers to:
defines EM level for speech as the “sound pressure level of a specified masking noise that
masks a speech signal to 50% probability of recognition”
• in individuals with normal hearing:
“the amount of effective masking . . . is equal to the number of decibels that a masking noise
shifts a speech recognition threshold.
when the masking noise and speech signal are presented simultaneously to the same ear”
23. Calibration of Effective Masking Level
Example
SRT is measured at 0 dB HL.
Speech spectrum noise is then presented to the same ear at 50 dB EM.
This EM level of 50 dB will shift the SRT to 50 dB HL.
Calibration of masking noise in EM level greatly simplifies clinical masking procedures.
When masking noise is calibrated in dB EM, then the decibel value indicated on the masking
level control will indicate the masking effect produced in the nontest ear.
24. CLINICAL MASKING PROCEDURES
• All approaches to clinical masking address two basic questions.
• First
what is the minimum level of noise that is needed in the nontest ear to eliminate its response
to the test signal?
• this is the minimum masking level that is needed to avoid undermasking (i.e., even with
contralateral masking, the test signal continues to be perceived in the nontest ear).
• Second
what is the maximum level of noise that can be used in the nontest ear that will not change the
true threshold or response in the test ear?
• this is the maximum masking level that can be used without overmasking (i.e., with
contralateral masking, the true threshold or response in the test ear has been changed).
25. “initial” masking level (in dB EM) during air-
conduction threshold testing
“Initial” masking level (in dB EM) during AC threshold testing:
Air-conduction threshold (in dB HL) of the nontest ear ( AC Nontest Ear)
Unmasked AC threshold in the left ear:
65 dB HL
Initial masking level:
5 dB EM
• initial masking level is calculated in the same manner regardless of the
air conduction transducer being used (i.e., supra-aural earphone or 3A
insert earphone).
26. “initial” masking level (in dB EM) during air-
conduction threshold testing
الزم ،فردی بین پذیری تغییر گرفتن نظر در برای
است
10
بل دسی
شود اضافه اولیه پوشش سطح به
.
یک
EM level
موثر میزان یک به افراد همه برای مشخص
نیست
.
علت
:
کالیبراسیون
EM
گروهی پاسخ میانیگن اساس بر
نرمال شنوایی با افراد از
.
Initial Masking Level = AC Nontest Ear + 10 dB
Initial Masking Level = AC Nontest Ear + 10 dB
= 5 dB HL + 10 dB
= 15 dB EM
27. “initial” masking level & minimum
masking level
It is important to differentiate the terms minimum masking level and initial masking level during
air-conduction threshold audiometry.
Minimum masking level is the:
minimum level of noise needed to eliminate the contribution of the nontest ear to establish the true
or correct threshold in the test ear.
Initial masking level is:
the first level of noise introduced to the nontest ear.
• This initial level of masking is often not sufficient to establish the threshold in the test ear; higher
levels of masking are often required.
28. initial masking level during bone-conduction
audiometry
• initial masking level during bone-conduction audiometry is equal to the air-conduction
threshold of the nontest ear.
• we will need to add the OE to the initial masking level to compensate for covering (i.e.,
occluding) the nontest ear with an earphone.
30. Occlusion Effect (OE)
When using supra-aural earphones, the following fixed OE values are recommended:
• 30 dB at 250 Hz, 20 dB at 500 Hz, and 10 dB at 1,000 Hz (Katz,2015; Gelfand, 2015).
• 20 dB at 250 Hz, 15 dB at 500 Hz, and 5 dB at 1,000 Hz (Diagnosis, 2007).
When using 3A insert earphones with deeply inserted foam eartips, the following values
are recommended:
• 10 dB at 250 and 500 Hz and 0 dB at frequencies of 1,000 Hz or higher. (Katz, 2014 ;
Gelfand, 2015; )
OE is decreased or absent in ears with conductive hearing impairment.
If the nontest ear exhibits a potential air-bone gap of 20 dB or more, then the OE should
not be added to the initial masking level at that frequency.
31. initial masking level during bone-conduction
audiometry
Need for masking the BC thresholds?
Unmasked BC threshold: 5 dB HL
Masked AC threshold Left ear :85 dB HL
Initial Masking level:?
32. Maximum Masking Level
Maximum masking level refers to:
• the maximum level of noise that can be used in the nontest ear that will not shift or change the
true threshold in the test ear.
Two factors influence maximum masking level during puretone audiometry:
(1) The bone-conduction threshold of the test ear (BC Test Ear)
(2) IA of the air-conducted masking stimulus
33. Maximum Masking Level
• Overmasking is more of a potential problem when?
• Bone-conduction sensitivity is very good in the test ear.
• Overmasking is generally not an issue when?
• Bone-conduction hearing sensitivity is poor in the test ear.
The poorer the bone-conduction hearing sensitivity is in the test ear, the greater the
levels of masking that can be used without overmasking.
36. Maximum Masking Level
محافظه بسیار اغلب ،پوشش سطح حداکثر تخمین
آن صحیح میزان از دقیقی نشانگر و ،است کارانه
نیست
.
(1
کارانه محافظه مقادیر گرفتن نظر در
IA
.
(2
طول در پوشش سطح حداکثر تخمین هنگام به
آستانه ادیومتری
AC
و
BC
،
True BC Test Ear
مشخص
نیست
.
های آستانه تنها ،پوشش سطح تعیین هنگام به
نیافته پوشش
BC
داریم را
.
37. Maximum Masking Level
Whenever an unmasked bone-conduction threshold is used, the resultant value is typically
smaller than the masking level that will actually result in overmasking.
Consideration of the maximum level of noise that can be used in the nontest ear can alert the
audiologist to the possibility of overmasking, particularly in cases of conductive hearing
loss when bone-conduction hearing sensitivity is very good.
Editor's Notes
Although white noise is an adequate masker, it is not the most efficient.
