masking - exam 2 Flashcards
purpose of masking
to prevent participation of the non-test ear in the hearing eval
occupy non-test ear so that any sound crossing from the test ear is not perceived by the non-test ear
required because of:
interaural attenuation
crossover
interaural attenuation
as sound travels from 1 side of the head to the other, a certain amount of energy is lost in transmission
loss of sound intensity = IA
BC cross hearing
always exists because the bones are close to each other, bone vibrator stimulates both cochleae regardless of placement
IA theoretically 0 dB
cannot be confident about which cochlea is responding unless we add masking
IA varies by…
transducer
freq of stimulus
individual skull properties
cross over
presence of sound in the non-test ear that results from stimulation of the test ear
results in invalid threshold measurement
primarily happens by bone conduction
shadow curve
representation on the audiogram of cross over
mimics threshold but shifted down IA from test ear
masking rule for AC
AC (the) - IA >= AC (nte) –> mask
test at every freq
or at PTA
IA values
higher IA = less sound into NTE
supra & circum aural headphones =
40 dB IA for pure tones
50 for speech
insert headphones =
50 dB IA for pure tones
60 for speech
masking rule for BC
always mask if ear-specific info is required
ABG (the) > 10 dB
white noise
broadband
can mask all freqs
narrowband noise
masking a pure tone most efficiently accomplished by freqs immediately surrounding that tone
only masks tone of interest
very efficient
plateau method (masking procedure)
present masking noise to NTE at 10 dB above threshold
present tone to TE at threshold
yes –> increase noise by 5 dB
no –> increase tone by 5 dB
repeat until yes to tone during 3 consecutive increases of the NOISE
what happens if you don’t mask when cross hearing occurs
hearing loss can be underestimated
type of hearing loss can be misdiagnosed
if an audiogram has unmasked & masked symbols, which symbols would you use to interpret the type of hearing loss
masked
does a ‘no response’ count toward threshold
no
