Masking ESSENTIALS

Interaural attenuation

indicates how much energy is reduced between ears

Why do we need to know IA?

helps us to assign masking noise to the non-test ear and keep it busy while we assess the test ear.

Interaural attenuation is ultimately the difference between…

the signal perceived in the test ear and in the non- test ear

Interaural attenuation values for supra-aural headphones:

40 dB for all tones and speech

Interaural attenuation values for insert earphones

75 dB 250-1000 Hz

50 dB 1500-8000 Hz

IA for inserts for speech

60 dB

It’s widely accepted that the IA for BC is…

0 dB HL

When to Mask-Air Conduction

mask anytime the sound from the test ear may cross over to the non-test ear

What masking conditions to consider for AC?

1. Interaural attenuation

2. Unmasked air conduction threshold in the test ear (HL threshold)

3. Bone conduction threshold in the non-test ear

When cross hearing occurs, the primary mode of stimulation is…

BC

Mask AC if…

AC (test ear) – BC (non-test ear) ≥ IA

AC (test ear) – AC (non-test ear) ≥ IA

When to Mask-Bone Conduction?

whenever the results of unmasked bone-conduction audiometry suggest the presence of an air-bone gap in the test ear of 15 dB HL or greater

Air-Bone Gap (test ear) ≥ 15 dB HL or…

Air-Bone Gap = AC (test ear) – Unmasked BC

If there are ABGs of 10 dB HL or less…

no contralateral masking is needed.

When to Mask-Speech Audiometry?

presentation level of the speech signal (in dB HL) in the test ear (Presentation Level (test ear)) equals or exceed the best puretone bone-conduction threshold in the non-test ear (Best BC (nontest ear) by a conservative estimate of IA

Masking speech: Presentation Level (test ear) – Best BC (non-test ear) ≥ IA or

ST (test ear) – ST (non-test ear) ≥ IA

Since speech is a ______ signal, find best bone conduction from ______through ______

broadband, 500 through 4000 Hz

What masking noise do you use for puretones?

NBN

What masking noise do you use for speech testing?

speech noise

What is masking noise calibrated as?

EM, effective masking

Initial Masking Level

Initial Masking Level = AC (nontest Ear) + OE + 10 dB

When we occlude (block) the non-test ear with earphones, we need to add _____________

an occlusion effect factor

By blocking the ear, we increase ______

sound pressure reaching the cochlea

Supra-aural earphones have more____

occlusion effect than insert earphones

Occlusion effect (bone conduction) for supra-aural headphones:

30 dB for 250 Hz (not typically tested)

20 dB for 500 Hz

10 dB for 1000 Hz

Occlusion effect (bone conduction) for insert earphones:

• 10 dB for 250 Hz (not typically tested)

• 10 dB for 500 Hz

Plateau Method of Masking-Hood 1960 (2 possible outcomes)

1. No measured threshold shift with masking

2. Measured threshold shift with masking

Plateau Method of Masking Steps:

1. Introduce masking noise to the non-test ear at the initial masking level.

• Retest puretone threshold (test ear)

2. If patient responds to tone, increase noise by 5 dB HL. If there is no response to the tone

(with contralateral noise), increase the tone in 5 dB steps until the patient responds

3. Plateau is reached when the noise has been increased 20 dB (three 5 dB steps) over the initial masking level without shifting the test ear tone.

4. Masked threshold is the dB HL of the tone when masking plateau was obtained.

THE MASKING DILEMMA

may occur when you apply the minimum masking, but you are quickly overmasking.

May happen with bilateral mild to moderate conductive hearing loss or an asymmetrical hearing

loss

Insert earphones may help because IA increases

CENTRAL MASKING

When contralateral masking produces a shift in the test ear even when overmasking isn’t

possible.

It’s believed that this rare shift may be caused by a slight change in the central nervous system.