Exam 2 Flashcards
What is masking?
The ability of one acoustic signal to obscure the presence of another acoustic signal so it cannot be detected
Keeping one ear busy so that we can get accurate results for the ear being tested
What does masking do?
Raises the threshold of audibility for one sound by the presence of another (masking)
What is the test ear?
Ear that the signal is directed to
What is the non test ear?
Ear receiving masking noise
Why is masking needed?
- Human ears are not acoustically isolated so sound crosses over to both ears
- Tones presented via air conduction to one ear can be loud enough to stimulate the opposite ear via bone conduction (crossover or cross hearing)
What is crossover?
- When a tone is presented to one ear at a given level and is heard at a lower level in the opposite ear
- Determined by the level of tone in the test ear and loss in signal strength as it passes to the opposite non test ear
What is inter-aural attenuation?
- Difference in level of the acoustic signal at the two ears
- Difference in level from test ear to non test ear
- Decrease in the level of an acoustic signal (in dB) as it passes from one ear to the cochlea of the opposite ear
True or false: type of transducer used affects interaural attenuation
True
What is the lowest acceptable interaural attenuation for supra-aural headphones? Insert earphones?
40 dB supra aural
70 dB insert earphones
Anytime the _ conduction threshold in one ear differs from the _ or _ conduction threshold in the other ear by _ or _ dB, crossover may have occurred and the _ ear will need to be isolated acoustically
air
air, bone
40, 70
better
What is the interaural attenuation for bone conduction?
0 dB
Placing bone vibrator on the mastoid, assume that the tone may be heard in both ears
With bone oscillator testing, we can assume that the patient hears the tone in the ear with the better __
Cochlea
We will always mask bone conduction testing if there is an air bone gap of ____ dB HL or more
15
Why do we use masking?
- To determine the hearing sensitivity of one ear while making sure that the test signals are not heard in the opposite ear
- Allows us to acoustically isolate the test ear
How is masking performed for pure tones?
- Noise presented in the non test ear as narrow band noise centered around the frequency that is being tested
- Follows the critical band theory, meaning we play noise right around the frequency that we are interested in and effectively mask without needing any extra frequencies
How is masking performed for speech audiometry?
- use a speech shaped noise that mimics everyday human speech
- shaped to have the spectral energy similar to that of speech
What is the first step when determining if masking is needed?
Confirm if crossover occured
Procedure for confirming cross over
- present narrow band of noise continuously to the non test ear at a level 10 dB above the threshold in that ear
- measure the threshold of the test ear again
- If the threshold increases by 5 to 10 dB, the original threshold was the result of crossover
After crossover has been confirmed, what procedure is followed to find the true threshold of the test ear?
- Increase the noise in the non test ear incrementally until the threshold in the test ear no longer increases
- Looking for a plateu, where multiple increases in noise in non test ear does not cause a change in the test ear threshold
What is the plateu?
Levels between undermasking and overmasking at which true threshold of the test ear is established
What is undermasking?
- Occurs when a masking noise presented to the non-test ear is of insufficient intensity to prevent the test signal from being heard in the non-test ear
- Turning up volume and threshold still changing so not enough for acoustic isolation
What is overmasking?
- Occurs when a masking noise presented to the non-test ear is intense enough to shift the threshold in the test ear
- Too much noise in the test ear to the point where noise is crossing over to the test ear rather than staying in the non test ear and keeping it busy
- Test ear has been compromised
On the audiogram, symbols are ___ to indicate that masking was used
- changed
- level of masking is also sometimes indicated
What is the minimum masking level?
- Lowest level of noise necessary to mask the non test ear
- usually 10 dB above air conduction threshold in non test ear