Masking in Audiology (incl. the Rules of Masking) - An Overview

Summary

This video explains the importance of masking in audiology, particularly when testing one ear. It covers how sound can cross over to the opposite ear, affecting the accuracy of hearing tests. The video introduces interaural attenuation, which varies depending on the type of earphones or bone conduction used. It also outlines the three essential rules of masking: masking when there is a significant air conduction threshold difference, masking for bone conduction thresholds when there’s an air-bone gap, and masking when there is a large air conduction discrepancy between the tested ear and the non-tested ear. These rules help ensure accurate hearing assessments.

Takeaways

• 😀 Masking in audiology is crucial for ensuring accurate hearing test results by isolating the test ear from potential sound leakage to the non-test ear.
• 😀 Sound can leak from one ear to the other during hearing tests, especially when headphones are used, leading to incorrect test results if not properly masked.
• 😀 Interaural attenuation refers to the reduction of sound intensity as it travels from the test ear to the non-test ear through the skull bones.
• 😀 With over-the-ear headphones, interaural attenuation is typically around 40 dB, while with insert headphones, it's higher at around 60 dB, reducing the risk of sound leakage.
• 😀 Bone conduction vibrators have little to no interaural attenuation (0-10 dB), which means sound is almost equally heard by both ears.
• 😀 Masking ensures the non-test ear does not respond to the test sound, thus preventing false thresholds due to cross-over sound detection.
• 😀 Rule 1 of masking states that masking is needed when there is a greater than 40 dB difference between the air conduction thresholds of the test and non-test ear using over-the-ear headphones.
• 😀 Rule 2 of masking is applied when there is a significant air-bone gap (greater than 10 dB) in the tested ear. It helps ensure that sound detected by the non-test ear via bone conduction doesn't interfere with the test results.
• 😀 Rule 3 applies when there is a greater than 40 dB difference between the air conduction threshold of the test ear and the bone conduction threshold of the non-test ear.
• 😀 The goal of all three rules is to ensure the sound presented to the test ear is accurately detected by that ear, without interference from the non-test ear, which could lead to misdiagnosis.

Q & A

What is interaural attenuation (IA)?

Interaural attenuation is the reduction in sound intensity as it travels from the test ear to the non-test ear through the bones of the skull. The amount of attenuation depends on the method of sound delivery, such as over-the-ear headphones, insert headphones, or bone conduction vibrators.

Why does masking become necessary in audiometry?

Masking is necessary in audiometry to ensure accurate hearing test results. When sound is presented to one ear through headphones, some of the sound energy can leak to the opposite ear. Without masking, the non-test ear might detect the sound, leading to false results for the test ear.

How does the method of sound delivery affect interaural attenuation?

The method of sound delivery affects interaural attenuation significantly. For over-the-ear headphones, IA is typically around 40 dB, while with insert headphones, IA is typically around 60 dB. Bone conduction vibrators have much lower IA, ranging from 0 to 10 dB, meaning little to no attenuation occurs.

What are the three rules of masking in audiometry?

The three rules of masking in audiometry are: 1) Mask if the air conduction threshold of the test ear is 40 dB or greater than that of the non-test ear when using over-the-ear headphones. 2) Mask if there is a significant air-bone gap (>10 dB) in the test ear. 3) Mask if there is a greater than 40 dB difference between the air conduction of the test ear and the bone conduction of the non-test ear.

What happens if the air conduction threshold of the test ear is 40 dB or greater than that of the non-test ear?

If the air conduction threshold of the test ear is 40 dB or greater than that of the non-test ear, sound may leak to the non-test ear due to interaural attenuation. This makes it difficult to determine if the sound is actually being detected by the test ear or the non-test ear, so masking is required.

Why does a significant air-bone gap in the test ear require masking?

A significant air-bone gap (greater than 10 dB) in the test ear requires masking because the bone conduction route allows sound to travel to the non-test ear, potentially leading to false results. Masking ensures that the non-test ear doesn’t detect sound during the test.

What is the rationale behind Rule 3 of masking in audiometry?

Rule 3 of masking states that if there is a greater than 40 dB difference between the air conduction threshold of the test ear and the bone conduction threshold of the non-test ear, masking is necessary. This is because the non-test ear might detect sound via bone conduction, leading to inaccurate results.

How does bone conduction affect masking requirements?

Bone conduction affects masking requirements because it can transmit sound to the non-test ear with little to no attenuation. If bone conduction thresholds are similar between ears or if the air conduction threshold difference is significant, masking may be required to prevent the non-test ear from responding.

Why does the sound energy presented to the test ear sometimes cross over to the opposite ear?

Sound energy presented to the test ear can cross over to the opposite ear because, above a certain amplitude, the sound waves can vibrate the bones of the external ear canal and skull, stimulating the opposite ear. This is called cross-hearing or sound leakage, which is particularly significant with higher intensity sounds.

What is the main difference between over-the-ear headphones and insert headphones regarding masking?

The main difference is the interaural attenuation (IA). Over-the-ear headphones typically have an IA of around 40 dB, while insert headphones have a higher IA of around 60 dB. This means that insert headphones are less likely to cause crossover, making them more effective in preventing the non-test ear from hearing the sound.