Cross masking, often called masking in audiology, is a technique used during hearing tests to isolate the ear being tested and prevent sound from "crossing over" to the non-test ear. The main goal is to ensure accurate results by preventing the better ear from responding to the test signal intended for the weaker ear.
The "Cross-Over Problem"
As the reference indicates, the core reason for masking is the "cross-over problem." This occurs when a loud sound presented to one ear is intense enough to stimulate the cochlea of the opposite, non-test ear. This happens via bone conduction. Therefore, even if the ear being tested has a significant hearing loss, the better ear might pick up the sound, leading to a false impression of hearing ability in the ear under evaluation.
How Masking Works
Masking involves introducing noise into the non-test ear while administering the hearing test to the test ear. This noise effectively "occupies" the non-test ear, preventing it from responding to the test signal presented to the test ear. By using this noise, it ensures that the response obtained during the test truly reflects the hearing ability of the ear being tested.
Why is Masking Important?
Masking is vital for accurate audiometric testing, particularly when:
- There's a significant difference in hearing thresholds between the two ears (an interaural attenuation difference).
- Bone conduction testing is being performed.
Failing to mask when necessary can lead to misdiagnosis and inappropriate management of hearing loss.
Example Scenario
Imagine testing the right ear of a patient, and you suspect the left ear has significantly better hearing. Without masking, if the sound presented to the right ear is loud enough, it could be heard by the left ear. As a result, the audiogram might show that the right ear hears better than it actually does. By introducing masking noise to the left ear, you eliminate its ability to respond to the signal intended for the right ear, providing a true measure of the right ear's hearing threshold.
