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Questions and Answers
What is the primary reason individuals with conductive hearing loss do not experience an occlusion effect?
At which frequency do recommended correction factors occur?
What is the purpose of subtracting 35 dB from the presentation level of the unmasked speech recognition threshold?
What occurs when it is impossible to mask the non-test ear effectively without exceeding the maximum permissible masking level?
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What is the recommended correction factor at 250 Hz?
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What is the purpose of adding the air-bone gap of the non-test ear in masking for speech recognition threshold?
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What type of hearing loss is least likely to experience an occlusion effect?
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What is the result of a masking dilemma?
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What is the recommended correction factor at 500 Hz?
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What is the primary purpose of masking for word recognition score?
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Study Notes
Clinical Masking
- Masking: the process of raising the threshold of hearing for one sound by the presence of another sound, with the amount of threshold raise expressed in decibels.
- Effective masking: the ability of a masking noise to mask a signal of known frequency and intensity, based on the spectrum of the masking noise.
When to Mask?
- Masking is needed for AC when the A/C threshold of the test ear (TE) exceeds the B/C or A/C threshold of the non-test ear (NTE) by 40 dB or more.
- Masking is needed for pure tone BC testing when the BC threshold differs from the AC threshold of the same ear by more than 10 dB (i.e., when suspecting CHL).
- Masking is needed for SRT testing when the SRT of the TE exceeds the SRT or the B/C of the NTE by 45 dB or more.
- Masking is needed for WRS testing when the PL in the TE exceeds the SRT or the best B/C threshold in any of the speech frequencies (500, 1000, or 2000 Hz) of the NTE by 35 dB or more.
Central Masking
- Threshold shift in the TE resulting from masking the NTE that is not due to crossover.
- Even small to moderate amounts of masking noise in the NTE result in a threshold elevation of the TE by 5-7 dB.
- Mechanism: inhibitory response in the CNS.
- Average: 5 dB.
Masking Noises
- BBN or White Noise: 2 to 6 /8 kHz.
- Narrow Band Noise.
- Speech Noise: 300-3000 Hz.
Masking Magnitude
- Masking dilemma: when no masking plateau is present and the minimum necessary masking and the maximum permissible masking are the same.
- Over masking: when the masking noise level in the NTE is equal to or exceeds the interaural attenuation plus the B/C threshold of the TE.
Masking for Pure-Tone Air-Conduction and Bone-Conduction
- Calculate the starting level by adding the non-test ear threshold, correction factor, and safety factor.
- Introduce masking and increase the masking level until a plateau is reached or the test ear threshold shifts to the limits.
Occlusion Effect
- Improvement in low frequency BC thresholds due to occlusion of the ear.
- Individuals with sensorineural hearing loss or normal hearing are most likely to experience an occlusion effect.
- Occurs at 1000 Hz and lower.
- Recommended correction factors:
- 250 Hz: 20 dB
- 500 Hz: 15 dB
- 1000 Hz: 5 dB
Masking for Speech Recognition Threshold and Word Recognition Score
- Calculate the starting level by subtracting a certain value (35 dB or 25 dB) from the presentation level of the unmasked speech recognition threshold or word recognition score, and adding the air-bone gap of the non-test ear.
- Introduce masking and use the subtraction procedure to determine the masking level, accounting for the minimum interaural attenuation.
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Description
This quiz covers the concept of clinical masking in audiological measurement, including the definition and application of masking signals.
