Masking in audiology is important for two main reasons 1. To separate different parts of the auditory system during bone and air conduction testing, and 2. To isolate the ears and determine the severity of hearing loss in each 

Bone conduction testing bypasses the middle and outer ear and sends sound directly to the inner ear. Clinicians perform this test using a bone oscillator headband that vibrates the entire skull. With just this headband on, it can be impossible to tell which inner ear is responding to the stimuli presented. In this case, we would use masking to separate the ears and determine the severity of hearing loss in each individual.  

With cross-hearing, sound can be loud enough that although it is being presented to one ear, it is detected by the other. In this case, we need to isolate each ear and determine which is responding. This, again, helps to determine the severity of hearing loss in each ear individually.  

Masking in audiology is performed by presenting noise – usually narrowband noise – to the ear that is not being tested (non-test ear). Stimuli will be simultaneously presented to the test ear. By introducing this noise to the non-test ear, we can ensure that only the intended ear is responding.

Step 1 - Determining Presentation Level 

A clinician will first decide upon an initial level of masking stimuli to present to the contralateral ear. This is done individually at each frequency and relies upon the air conduction threshold of the contralateral ear at that frequency. Providers may begin at the air conduction threshold, but often add a predetermined dB level, for example an extra 10 – 20 dB, in their initial presentation

Step 2 - Obtaining a Response 

Masking noise is presented via air conduction and can be used to validate bone or air conduction thresholds. A clinician will place their selected transducer, if they haven’t already done so, and masking will be presented via headphones or insert earphones. The patient will be instructed to ignore the background noise and respond to the tone as they had at the beginning of the test. They will then wait for the patient’s response.

Step 3 - Finding the Plateau

Once a response is obtained, the level of the masking noise will be increased until a plateau is reached. The plateau is the level of masking noise that is sufficient to avoid cross-hearing of the contralateral ear, but not so loud that cross hearing of the masking noise occurs in the test ear. When cross hearing of the masking noise in the test ear occurs and a response from that ear cannot be obtained, this is called “over masking” or a “masking dilemma.” 

Yes, masking can add time to a standard pure-tone audiometry test, as additional steps and adjustments are required to apply the masking noise properly.