masking basic principles clinical approaches. masking = preventing crossover given enough intensity...

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MASKING MASKING BASIC PRINCIPLES BASIC PRINCIPLES CLINICAL APPROACHES CLINICAL APPROACHES

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Page 1: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

MASKINGMASKING

BASIC PRINCIPLESBASIC PRINCIPLES

CLINICAL APPROACHESCLINICAL APPROACHES

Page 2: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Masking = Preventing Crossover

• Given enough intensity any transducer can stimulate the opposite cochlea

• Enough intensity to cross over = _________.

• Therefore some unmasked thresholds will be suspect and require masking.

Page 3: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

IA in Supra-aural Earphones

• The range for headphones is 40 - 80 dB

• Depends on:

– frequency,

– headphone placement

– size of the patient’s head

• To be safe, use 40 dB as the IA for headphones

• i.e., when HL exceeds opposite ear thresholds by 40 or more, you may need to mask.

Page 4: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

IA for Insert Earphones

• Varies with:

– frequency

– depth of placement

– patient

• IA is greater for inserts than headphones

• Once again being safe we can use 60 dB as IA for inserts.

Page 5: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Interaural Attenuation for InsertsFrom:Instructions for the use of E-A-RTONE ® insert earphones

Proper insertion depth is necessary to achieve

maximum ambient noise attenuation and

interaural attenuation.

The graph depicts interaural attenuation as

a function of insertion depth.

Page 6: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

IA for Bone Conduction

• 0 dB

• However, we aren’t interested in clinically insignificant air-bone gaps

(Air-Bone Gap = 15 dB or more)

• Mask any unexplained air-bone gaps

Page 7: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

When you DO need to mask:

• Unilateral Conductive HL

• Bilateral Conductive HL

• Unilateral SNHL (differing by more than IA)

(GENERALLY)

Page 8: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

When you don’t need to mask

• Hearing WNL bilaterally

• Bilateral symmetrical SNHL

(GENERALLY)

Page 9: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

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ED

TO

MA

SK

?N

EE

D T

O M

AS

K?

Page 10: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

NE

ED

TO

MA

SK

?N

EE

D T

O M

AS

K?

Page 11: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Masking Principles

• Remember: Crossover is always via Bone Conduction!!!

• With masking, a 5 dB shift in threshold may occur due to central masking.

• When you introduce masking to an ear, the BC and AC thresholds will be affected the same amount.

• Masking must be above the threshold of the masked ear to have an effect on that ear.

Page 12: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

What kind of Noise?

• For Pure Tones?

• For Speech?

• Narrow Band Noise

• Pink or Speech Noise– or white noise

Page 13: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

dB EM

• Calibration of decibel level of maskers

• Level to which tone threshold will be shifted in the presence of the masker.

e.g., a 45 dB EM narrow band noise centered at 2000 Hz would raise someone’s threshold for a

2000 Hz tone to 45 dB HL **

Page 14: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Ranges of Masking

20

30

40

50

60

70

80

90

100

20 30 40 50 60 70 80 90

Masker Level (dB EM)

Thr

esho

ld in

TE

(dB

HL

)

Under Sufficient Over

Page 15: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Masking

Page 16: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea
Page 17: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Normal

Mild

Moderate

Mod-

Severe

Severe

Profound

0

10

20

30

40

50

60

70

80

90

100

110

250 500 1K 2K 3K 4K 6K 8K

Am

plit

ude

in d

B H

LFrequency in KHz

X X X X X

Where is unmasked BC for AD at all frequencies?

Page 18: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Normal

Mild

Moderate

Mod-

Severe

Severe

Profound

0

10

20

30

40

50

60

70

80

90

100

110

250 500 1K 2K 3K 4K 6K 8K

Am

plit

ude

in d

B H

LFrequency in KHz

X X X X X

Unmasked Bone

^ ^ ^ ^ ^

Page 19: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Normal

Mild

Moderate

Mod-

Severe

Severe

Profound

0

10

20

30

40

50

60

70

80

90

100

110

250 500 1K 2K 3K 4K 6K 8K

Am

plit

ude

in d

B H

LFrequency in KHz

X X X X X

Headphones maximum NB masking before crossover: 40 dB

Page 20: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

Normal

Mild

Moderate

Mod-

Severe

Severe

Profound

0

10

20

30

40

50

60

70

80

90

100

110

250 500 1K 2K 3K 4K 6K 8K

Am

plit

ude

in d

B H

LFrequency in KHz

X X X X X

Inserts maximum NB masking before crossover: 60 dB

Page 21: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea
Page 22: MASKING BASIC PRINCIPLES CLINICAL APPROACHES. Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea

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