MASKING BASIC PRINCIPLES CLINICAL APPROACHES

Masking = Preventing Crossover Given enough intensity any transducer can stimulate the opposite cochlea Enough intensity to cross over = _________. Therefore some unmasked thresholds will be suspect and require masking.

IA in Supra-aural Earphones The range for headphones is dB Depends on: –frequency, –headphone placement –size of the patient’s head To be safe, use 40 dB as the IA for headphones i.e., when HL exceeds opposite ear thresholds by 40 or more, you may need to mask.

IA for Insert Earphones Varies with: –frequency –depth of placement –patient IA is greater for inserts than headphones Once again being safe we can use 60 dB as IA for inserts.

Interaural Attenuation for Inserts From:Instructions for the use of E-A-RTONE ® insert earphones Proper insertion depth is necessary to achieve maximum ambient noise attenuation and interaural attenuation. The graph depicts interaural attenuation as a function of insertion depth.

IA for Bone Conduction 0 dB However, we aren’t interested in clinically insignificant air-bone gaps (Air-Bone Gap = 15 dB or more) Mask any unexplained air-bone gaps

When you DO need to mask: Unilateral Conductive HL Bilateral Conductive HL Unilateral SNHL (differing by more than IA) (GENERALLY)

When you don’t need to mask Hearing WNL bilaterally Bilateral symmetrical SNHL (GENERALLY)

NEED TO MASK?

Masking Principles Remember: Crossover is always via Bone Conduction!!! With masking, a 5 dB shift in threshold may occur due to central masking. When you introduce masking to an ear, the BC and AC thresholds will be affected the same amount. Masking must be above the threshold of the masked ear to have an effect on that ear.

What kind of Noise? For Pure Tones? For Speech? Narrow Band Noise Pink or Speech Noise –or white noise

dB EM Calibration of decibel level of maskers Level to which tone threshold will be shifted in the presence of the masker.  e.g., a 45 dB EM narrow band noise centered at 2000 Hz would raise someone’s threshold for a 2000 Hz tone to 45 dB HL **

Ranges of Masking

Masking

Normal Mild Moderate Mod- Severe Profound K 2K 3K 4K 6K 8K Amplitude in dB HL Frequency in KHz X X X XX Where is unmasked BC for AD at all frequencies?

Normal Mild Moderate Mod- Severe Profound K 2K 3K 4K 6K 8K Amplitude in dB HL Frequency in KHz X X X XX Unmasked Bone ^ ^ ^ ^ ^

Normal Mild Moderate Mod- Severe Profound K 2K 3K 4K 6K 8K Amplitude in dB HL Frequency in KHz X X X XX Headphones maximum NB masking before crossover: 40 dB

Normal Mild Moderate Mod- Severe Profound K 2K 3K 4K 6K 8K Amplitude in dB HL Frequency in KHz X X X XX Inserts maximum NB masking before crossover: 60 dB

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