When measuring bone-conduction thresholds in an ear with an air-bone gap, why must masking noise always be delivered to the non-test ear?
- A Because interaural attenuation for bone conduction is approximately 40 dB
- B Because the vibrator itself generates acoustic noise audible to the opposite ear
- C Because interaural attenuation for bone conduction is essentially 0 dB, so the skull delivers the signal to both cochleae ✓
- D Because masking prevents the patient from feeling the vibration cutaneously
Correct answer: C. Because interaural attenuation for bone conduction is essentially 0 dB, so the skull delivers the signal to both cochleae
Explanation
The skull conducts vibratory energy so efficiently that interaural attenuation for bone conduction is effectively zero: whatever reaches one cochlea reaches the other, regardless of where the oscillator sits. Therefore the non-test cochlea can always respond, falsely improving apparent bone thresholds and shrinking the measured air-bone gap. For supra-aural air-conduction receivers interaural attenuation is roughly 40 to 50 dB, so masking there is needed only when the gap between ears exceeds it.
Reference: Katz, Handbook of Clinical Audiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.