12 - More on Masking

Question 1

What is a “shadow” audiogram?

Answer 1

A shadow audiogram is when the unmasked AC results of one ear “shadow” the results of the other ear because the better ear is responding.
Key indicators:
-asymmetry
-40 dB or greater difference
-dB HL “shadow” depends on individual’s actual IA

Question 2

Name 3 things that can influence IA

Answer 2

1. Subject variability
   - skull properties
2. Frequency spectrum of the test signal
   - pure tone frequency
3. Earphone transducer type
   - BC oscillator
   - supra-aural earphones
   - insert earphones

Question 3

Should we test unmasked BC bilaterally?

Answer 3

ONLY if you suspect an air-bone gap

Question 4

What order should we test unmasked BC in if testing bilaterally?

Answer 4

1. unmasked BC in worse AC ear
2. air-bone gaps > 10 dB for worse AC ear -> mask BC if required
3. air-bone gaps > 10 dB for better ear -> test unmasked BC for better ear

Question 5

Masking is usually performed in the following order: unmasked AC, unmasked BC, masked BC, masked AC.
What can you do to save time if you discover an asymmetric HL after AC?

Answer 5

After masked AC, you can tell which ear to mask BC so you don’t always have to mask bilaterally

Question 6

When graphing TE tone vs NTE noise during masking, what do the 3 parts of the graph show?

Answer 6

Undermasking (rising before plateau), Plateau, Overmasking (rising after plateau)

Question 7

No masking plateau can indicate which 2 things?

Answer 7

1. Masking Dilemma

2. “Dead” ear

Question 8

What is the SF (safety factor) in IML used to adjust for?

Answer 8

Central masking and test-retest reliability
-Central masking is a threshold shift in TE resulting from masking noise in NTE (not crossover - an inhibitory response within the CNS that affects both pure tone and speech thresholds by a 5 dB shift, on average)
Safety factor of 10 dB covers this and test/re-test reliability of -5 dB