Lecture 8 - Clinical Masking Flashcards
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?
- Pure tone air conduction assessment
- Pure tone bone conduction assessment
- Speech recognition threshold assessment
- 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?
0-10 dB
- 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?
- Start out with 10 dB + the AC threshold in the non-test ear
- Re-assess masked threshold in test ear
- Increase effective masking level by 5 dB in non-test ear
- Reassess threshold in test ear
- Continue until you reach a masked threshold in test ear that remains stable over 15-20 dB of increments in EML in NTE
- 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