masking for pure tone audiometry

What is interaural attenuation (IA)?

The amount of sound energy lost as it crosses from the test ear (TE) to the non-test ear (NTE).

What is the IA for supra-aural headphones?

40 dB.

What is the IA for insert earphones?

55 dB.

What is the IA for a bone vibrator?

0 dB.

What does low IA mean?

There is a higher risk of cross-hearing.

How does physical contact with the head affect IA?

More physical contact causes more bone-conduction crossover and lower IA.

How do you calculate crossover level?

Test ear level minus IA.

If a 70 dB HL tone is presented through insert earphones, what reaches the NTE?

70 - 55 = 15 dB HL.

When is air-conduction masking needed?

When the TE AC threshold minus the NTE BC threshold is greater than IA.

When is bone-conduction masking needed?

When the air-bone gap in the TE is greater than 10-15 dB.

What is cross-hearing?

A perceptual phenomenon where the listener hears the signal in the NTE cochlea.

What is crossover?

A physical phenomenon where sound energy presented to one mastoid reaches both cochleae.

When does BC crossover occur?

At all presentation levels.

When does AC crossover occur?

At high intensity levels when sound is loud enough to set the skull into vibration.

Which ear receives the target pure tone?

The test ear (TE).

Which ear receives the masking noise?

The non-test ear (NTE).

What type of noise is used to mask pure tones?

Narrow-band noise (NBN).

Why is narrow-band noise effective?

It is an effective masker for pure tones.

What is the purpose of contralateral masking?

To prevent the NTE from detecting sound crossing over from the TE.

What is the initial masking level?

The starting intensity of masking noise presented to the NTE.

How do you calculate the initial AC masking level?

AC threshold of the NTE + 10 dB.

What makes a masker effective?

Its level must be above the NTE threshold, with a 10 dB cushion.

What is undermasking?

The TE threshold goes up as masking increases; the NTE is still being evaluated.

What is effective masking (plateau)?

The TE threshold stays constant over a range as masker level increases.

What is overmasking?

The TE threshold increases again because the masker crosses over to the TE.