Chapter 4
Recognizing the Need for Masking
Overview
Because the mCalc app does not use standard audiometric symbols, and the mQuest game shows only one frequency of the audiogram, this chapter reviews ‘when to mask’ using the traditional audiogram. Both air- and bone-conduction need for masking are tested. Assume insert earphones were used6 The masking rules to use are as follows:
- For air-conduction, if the poorer ear threshold is 50 or more dB worse than the better ear AIR-conduction threshold, then masking is needed in the non-test ear.
- For air-conduction, if the poorer ear threshold is 50 or more dB worse than the better ear BONE-conduction threshold, then masking is needed in the non-test ear.
- For bone-conduction testing, if there is, or if there is the possibility of, a 15 dB or greater air-bone gap in the test ear, then the non-test ear needs to be masked.
Assume Use of Insert Earphones
Question 1
Figure 4-1
At which frequencies is masking required for air-conduction testing?
Click all that apply
Answer 4-1
Use rule 1: For air-conduction, if the poorer ear threshold is 50 or more dB worse than the better ear AIR-conduction threshold, then masking is needed in the non-test ear.
The masking would be put into the RIGHT ear, by AIR-conduction.
Question 2
Figure 4-2
At which frequencies is masking required for air-conduction testing?
Click all that apply
Which ear would receive the masking noise, and would that be input by air- or bone-conduction?
Show Answer
Answer 4-2
Use rule 2: For air-conduction, if the poorer ear threshold is 50 or more dB worse than the better ear BONE-conduction threshold, then masking is needed in the non-test ear. Note that rule 1 (compare air to air) would not have shown the need for masking at 1000 Hz.
The masking would be put into the RIGHT ear, by AIR-conduction.
Question 3
Figure 4-3
At which frequencies is masking required for air-conduction testing?
Click all that apply
Which ear would receive the masking noise, and would that be input by air- or bone-conduction?
Show Answer
Answer 4-3
Use rule 1: For air-conduction, if the poorer ear threshold is 50 or more dB worse than the better ear AIR-conduction threshold, then masking is needed in the non-test ear.
The masking would be put into the LEFT ear, by AIR-conduction.
Question 4
Figure 4-4
At which frequencies is masking required for air-conduction testing?
Click all that apply
Which ear would receive the masking noise, and would that be input by air- or bone-conduction?
Show Answer
Answer 4-4
Use rule 2. For air-conduction, if the poorer ear threshold is 50 or more dB worse than the better ear BONE-conduction threshold, then masking is needed in the non-test ear. Note that rule 1 (compare air to air) would not have shown the need for masking at 500 and 1000 Hz.
The masking would be put into the LEFT ear, by AIR-conduction.
Question 5 -- Bone-Conduction
Figure 4-5
For this next example, we switch to bone-conduction masking. At which frequencies is masking required for bone-conduction testing?
Answer 4-5
Use rule 3: For bone-conduction testing, if there is, or if there is the possibility of, a 15 dB or greater air-bone gap in the test ear, then the non-test ear needs to be masked.
The left ear shows an air-bone gap between the unmasked left ear bone-conduction threshold and the left air-conduction threshold at 500 and 1000 Hz. Since the bone-conduction testing is unmasked, the results could be for the right ear, and therefore there is need to mask the contralateral ear when conducting the bone-conduction testing on the right ear.
8 kHz is not traditionally tested by bone-conduction.
When masking is needed for the left ear bone-conduction threshold testing, the masking is put into the right ear by AIR conduction.
When masking is needed for the right bone-conduction threshold testing, the masking is put into the left ear by AIR conduction
Question 6 -- Air- and bone-conduction.
Figure 4-6
At which frequencies is masking required for air- and bone-conduction testing?
Click all that apply
Answer 4-6
Notes: right bone conduction testing at 1k and 2k shows only a 10 dB air-bone gap; the gap must be significant – 15 dB or greater – in order for masking to be required. The second masking rule alerts you to the need for masking at 1000 Hz for left air-conduction testing; the two air-conduction thresholds only differ by 45 dB, but the left air to unmasked bone-conduction threshold difference is 55 dB.
Question 7 -- Determining Need for 8kHz Air-Conduction Masking.
This next case is a special case – as you examine what needs masking, carefully consider if you need to mask when testing 8k Hz by air-conduction. (Bone-conduction testing is usually not conducted at 8k Hz.)
Figure 4-7
At which frequencies is masking required for air- and bone-conduction testing?
Click all that apply
Answer 4-7
Note that masking rule 2 asks you to compare the air-conduction threshold to the bone-conduction threshold, but you cannot test bone-conduction hearing at 8000 Hz. (Actually, many audiometers allow this testing now, but audiologists do not test 8000 Hz bone conduction routinely.) Bone-conduction testing measures cochlear sensitivity; regardless of whether we test 8k Hz, the cochlea hears by bone-conduction at this frequency. Mentally project the “bone line” out to 8000 Hz – use your guess of the 8000 Hz bone-conduction threshold to determine if masking should be used.
Because bone-conduction is not traditionally tested at 8000 Hz, the table above does not list bone-conduction masking as needed for this frequency.
Key Points
- Use the three masking rules in determining need for masking.
- Masking is always input by air-conduction, to the non-test ear; this is true regardless of whether testing air- or bone-conduction hearing.
- Bone-conduction hearing is not routinely tested at 8000 Hz, but consider the probable bone-conduction threshold that would probably be found when examining need for air-conduction threshold testing masking. If the “air to bone” difference would be 50 dB or greater if bone-conduction had been tested at 8000 Hz, then masking for air-conduction is appropriate.