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
What is the maximum effective masking level?
- Highest level of noise in the non test ear that would have crossed back over to the test ear if the level had been any higher (ceiling for accurate results)
- Equivalent to the bone conduction threshold in the test ear + the interaural attenuation
- Bone conduction threshold in the test ear + interaural attenuation
Bone conduction testing stimulates ____ cochlea
Both
Intra-aural attenuation for bone conduction is _ dB. We mask for BC when there is ___
0 dB
ABG (airbone gap)
A bone-conduction threshold indicates the sensitivity of the ____ cochlea.
Better
Bone-conduction can never be _____ than air-conduction.
Poorer
With air-conduction testing, crossover occurs when the signal is heard by _____
cochlea of the opposite ear
Intra-aural attenuationfor supra-aural earphones is, for insert earphones is
supra aural: 40 dB
inserts: 70 dB
To determine the true threshold of the poorer ear, masking is presented to the ____ while tones are presented to the ____
non test ear
test ear
When we mask, noise is presented via _____
air conduction
On an audiogram, _____ are changed to indicate that masking was used.
audiometric symbols
IA – TE – NTE – RE – LE – AC – BC –
IA – Interaural Attenuation TE – Test Ear NTE – Non-test Ear RE – Right Ear LE – Left Ear AC – Air Conduction BC – Bone Conduction
How do you calculate if masking is necessary for air conduction threshold using supraaural headphones? For bone conduction thresholds?
TE AC - NTE BC > or equal to 40 dB
TE AC - TE BC > 10 dB
How do you calculate minimum and maximum masking level?
Minimum: NTE AC + 10 dB
Maximum: TE BC + 40 dB
What is admittance?
Ease with which sound flows through a system
Measured with mmhos (ohm spelled backwards)
What is impedance?
Opposition to flow of acoustic energy
High impedance leads to low admittance
What equipments is used to measure acoustic immittance?
Tympanometer
Acoustic admittance measures: Probe assembly creates airtight seal at ___
opening of the ear canal
Acoustic admittance measures: loudspeaker presents a ___ tone
226 Hz
Acoustic admittance measures: pump reduces the air in the canal below ___ pressure then increases it above ___ pressure
A microphone measures the __ __ __ in the ear canal as the ___ ___ is changed
atmospheric pressure x2
sound pressure level, air pressure
Acoustic admittance is measured (in ___ units) as air pressure in the ear canal is changed from ___ to ___
Results are plotted on a graph called _____
mmhos, negative, positive
tympanogram
Tympanometry: what is peak Ya?
- Total acoustic admittance at the peak
- How much sound was admitted through the system
Tympanometry: what is peak Ytm?
- Just the admittance of the TM
- Go from positive tail to the peak
Tympanometry: what is TPP?
Tympanometic peak pressure
Pressure at which ya or Ytm is at its max
Look at peak and draw the line straight down
Tympanometry: what is tympanometric width? (TW)
Width of the tympanogram at 1/2 the height of Ytm (peak to tail)
Tympanometry: what is ear canal volume?
Acoustic estimate of the volume between the probe tip and TM
What is the cut off for TPP value?
-150 to 25 is normal
Normal ear tymps is a ….
Type A tymp
Tymps: negative middle ear pressure is a
Type C tymp
Tymps: middle ear problems is a
Type B tymp Foreign body (abnormally small volume) Otitis media (normal volume)
Type B tymps with high volume indicate
PE tubes or perforation in TM
Type As tymp details
Shallow type A
reduced compliance meaning system is more stiff and not moving as much as it should be
Type Ad tymps details
Deep type A
Hypermobile TM can be due to loose skin or breakage in the ossicular chain
Preak Ytm is over 2.0
What is the acoustic reflex?
Time-locked contraction of the stapedius muscle in response to an acoustic signal of sufficient intensity level and duration
Stiffening of the ossicular chain allows us to hear better in ___
Background noise
How are acoustic reflex thresholds tested? (procedure)
- middle ear system pressurized to point of max compliance
- present pure tone stimulus and measure changes in stiffness
- lowest intensity where a change in compliance can be measured is the acoustic reflex threshold
What stimuli are used for ART?
-Clicks, tones, complex noise stimuli
Ipsilateral ART stimuli tones, contralateral ART stimuli tones
Ipsilateral: 500, 1000, 2000 Hz
Contralateral: 500, 1000, 2000, 4000 Hz
ART Stimuli start at loudness of ___ and then take __ dB steps to find the threshold
Disordered ear will have threshold at ___, ____ or ___
85 dB HL, 5 dB
105, 110, or no response