audiology ch 9

Masking

Audiologic procedure used to prevent the non-test ear from responding to a stimulus presented to the test ear.

Why is masking necessary?

To ensure that the response obtained is coming from the test ear and not the non-test ear.

Cross-hearing

When a sound presented to one ear is heard by the opposite ear through bone conduction.

Test Ear (TE)

The ear being tested.

Non-Test Ear (NTE)

The ear receiving masking noise.

Interaural Attenuation (IA)

Sound loses strength when traveling between ears.

IA for Bone Conduction

0 dB.

IA for Supra-aural Headphones

Approximately 40 dB.

IA for Insert Earphones

Approximately 55 dB.

IA for Circumaural Headphones

Approximately 40 dB.

Narrowband Noise

narrow range of frequencies.

Speech Noise

Masking noise used to mask speech stimuli.

Effective Masking

Masking noise that is strong enough to prevent the non-test ear from responding.

Central Masking

A slight elevation in threshold in the test ear caused by noise presented to the opposite ear; commonly about 5 dB.

Air-Conduction Masking Rule

Mask when AC TE - BC NTE ≥ IA.

Bone-Conduction Masking Rule

Mask when the bone-conduction stimulus may be heard by the non-test ear and interaural differences indicate cross-hearing.

Air-Bone Gap (ABG)

The difference between air-conduction and bone-conduction thresholds.

ABG Formula

ABG = AC threshold - BC threshold.

When is BC masking necessary?

When the bone-conduction threshold may be heard by the non-test ear and masking is needed to isolate the test ear.

Initial Masking Level (IML)

The initial amount of masking noise presented to the non-test ear before the masking

procedure.

Plateau Method

A masking procedure in which masking noise is increased in steps while the test-ear threshold is monitored.

Masking Plateau

flat. The threshold stays the same even when masking noise increases.

Undermasking

Masking noise is insufficient to prevent the non-test ear from responding.

Overmasking

Masking noise is strong enough to cross back to the test ear and interfere with its response.

Masking Dilemma

A situation in which increasing masking noise causes overmasking before a stable masking plateau can be obtained.

Occlusion Effect

closing off the ear makes low sounds seem louder.

When is the occlusion effect greatest?

At low frequencies.

Why is masking used during speech audiometry?

To prevent the non-test ear from responding to speech presented to the test ear.