When is masking necessary for bone conduction threshold measurement?

Masking is necessary for bone conduction threshold measurement primarily when an air-bone gap is present. This air-bone gap indicates a difference between air conduction thresholds (which assess the entire auditory pathway) and bone conduction thresholds (which assess the inner ear directly by bypassing the outer and middle ear).

When there is an air-bone gap, sound presented through bone conduction can potentially stimulate the better hearing ear, especially in patients with unilateral or asymmetric hearing loss. In such cases, if the sound is loud enough, it may cross over to the opposite ear, giving a misleading representation of hearing ability. To ensure accurate measurement of the bone conduction threshold, masking is utilized to "block" the non-test ear, allowing for a true assessment of the threshold in the targeted ear.

This concept is fundamental in audiology as it ensures that any measured thresholds during the bone conduction test reflect the actual hearing capabilities of the ear being tested, taking into account any potential cross-hearing that might skew results.