Flashcards in Lecture 8 - Clinical Masking Deck (17):
What is effective masking?
# of dB that a masker shifts threshold of a test signal (in same ear), relative to quiet
What is actual masking?
How much a certain amount of masking has shifted a person's threshold
What is the purpose of clinical masking?
Put in masking in non-test ear to shift threshold in that ear so that it doesn't perceive signal that crossed over
In what situations can you mask?
1. Pure tone air conduction assessment
2. Pure tone bone conduction assessment
3. Speech recognition threshold assessment
4. Suprathreshold speech recognition testing
What is interaural attenuation?
The loss of signal intensity as the sound travels to the non-test cochlea
What is the interaural attenuation for pure tone air conduction?
Supra-aural earphones: 40-50 dB
- Due to through-the-head transmission (bc)
- Partially because of around-the-head transmission (ac)
Insert earphones, deep insertion: 75 dB
- Smaller amount of leakage
- Less through the head transmission
What is the interaural attenuation for bone conduction?
- Vibration of the skull
- The most sensitive cochlea responds to BC testing
When do I mask? (supra-aural earphones)
When the AC threshold in the test ear (TE) is 40 dB less than or equal to the bone conduction threshold in the non-test ear (NTE)
How can you use the Hood Plateau Technique for calculating the initial masking level?
1. Start out with 10 dB + the AC threshold in the non-test ear
2. Re-assess masked threshold in test ear
3. Increase effective masking level by 5 dB in non-test ear
6. Reassess threshold in test ear
7. Continue until you reach a masked threshold in test ear that remains stable over 15-20 dB of increments in EML in NTE
8. The masked threshold = true threshold in test ear
How can you determine the minimum and maximum masking level for pure tone AC thresholds?
Minimum Masking Level
Min EML = AC threshold (TE) - 35 dB + air-bone gap (NTE)
Maximum Masking Level
Max EML = BC threshold (TE) + IA (by AC)
When should you mask during bone conduction testing?
- You always have to mask when testing BC
Exception: AC thresholds are = bilaterally and = unmasked BC thresholds
How can you determine how the minimum amount of masking is needed in the non-test ear for BC testing?
Min EML = AC threshold (NTE) + 10 dB + occlusion
How much is the occlusion effect (OE) with insert earphones?
- OE is greater with shallow insertion
- OE is smaller with deep insertion
What is undermasking?
The tone that is presented to the test ear is picked up by the better cochlea
What is effective masking?
Masks the non-test ear from picking up the signal
What is overmasking?
There is so much masking noise that's going to the non-test ear, which means that the test ear is picking up that masking noise.