Masking (Puretone)

Why do we mask?

Crossover

What is crossover?

Occurs when an AC or BC signal is presented to the TE at an intensity great enough to stimulate the NTE

What is central masking?

• The threshold shift in TE when masking signal is introduced in NTE

• NOT due to crossover

• The general effect in minimal

Central masking effect averages ___ dB

5 dB

T/F: You can have a reverse Air-Bone Gap

True

What is the (typical) maximum dB level for conductive hearing loss?

65 dB

Unilateral hearing loss

Normal hearing in one ear; hearing loss in the other ear

Asymmetric hearing loss

Hearing loss in both ears; but the losses do not look the same

• Ex. mild loss in right, and mild sloping to moderately-severe in the left

Interaural Attenuation (IA)

The amount of energy lost during transmission of sound by AC or BC across and/or through the skull to the contralateral ear; The level of difference (in dB) of the signal b/w ears.

• Sound is being presented to one ear, and it travels (either through AC or BC) to the other ear

Crossover is reduced with ____ IA

High

IA = ?

IA = dB HL TE - dB HL NTE

What are the 3 factors that influence AC Interaural Attenuation?

1. Subject (pt) variability

2. Frequency spectrum of test signal

3. Earphone transducer type

IA values increase as frequency ________

Increases

• Meaning… that you’re more likely to crossover in lower frequencies

What is the conservative estimate for IA and supra-aural earphones?

40 dB across all frequencies

• That means… If between your R & L AC you are sitting at a 40 dB (or more) difference, YOU NEED TO MASK!

What is the conservative estimate for IA and insert earphones?

60 dB across all frequencies

• That means… If between your R & L AC you are sitting at a 60 dB (or more) difference, YOU NEED TO MASK!

What is the conservative estimate for IA and Bone Conduction? (regardless of mastoid or forehead placement)

0 dB across all frequencies

• Once the skull is vibrated, both cochleas are stimulated (0 dB could be vibrating both cochleas)

Occlusion Effect (OE)

Occluding the ear can enhance low-frequency BC threshold sensitivity

When you’re masking, keep the TE ________

Un-occluded

Does the OE factor into masking for Air Conduction?

No

• We only need to account for the OE when we are masking for Bone Conduction

At which frequencies do you need to consider the OE?

250, 500, & 1000 Hz

PT AC Testing: When is masking needed?

Masking in needed if the AC threshold of the TE exceeds the BC threshold of the NTE by the IA of the specific transducer.

• AC TE - BC NTE ≥ IA

• AC TE - AC NTE ≥ IA (formula that most people use)