Second 1/3 Semester Flashcards
What happens when two waves are in phase
Constructive interference
What happens when two waves are 180 degrees out of phase?
Destructive interference aka they cancel each other out
What happens when two waves are not in phase
Constructive and destructive interference
Standing waves
When a sound reflects off a surface, the reflecting wave can interfere with the other sound waves in the room causing spots of enhanced and diminished sound known as nodes and antipodes
*the nodes are known as standing waves
What do we use in booth to prevent standing waves
Warble tone
Where does resonance occur in a tube closed at both ends?
When the zero and 180 degree phase points are at the tube ends
* this is where the tube length is half the wavelength and it’s even and odd harmonics
Where does resonance occur in a tube closed at one end?
A frequency with a wavelength 4 times the length of the tube
- and odd harmonics
- mimics ear canal
What are the factors needs in a medium to transmit sound?
Mass and stiffness
What is it called when a medium resists the flow of sound energy?
Impedance
Equation for impedance
Z=force/velocity
- impedance is how hard it is to obtain a given velocity of molecule motion
- measured in a unit called rayl (ohm is unit for electric impedance)
Two main components of impedance
Resistance and reactance
Resistance
(R) impedance caused by friction
*opposes all frequencies equally
Reactance
(X) opposition produced by mass (x sub m) and stiffness (x sub s) of a medium
- mass and stiffness are opposites
- dependent on frequency
Equation for total opposition due to reactance
X sub t=x sub m - x sub s
Equation for mass reactance
(X sub m)= 2(pi)FM
M is mass
F is frequency
Equation for stiffness reactance
(X sub s)= S/2(pi)F
S is stiffness
acoustic impedance using pythagoran’s theorem
Z sub a= square root of R^2+ (2piFM - s/2piF)^2
when do we have the resonant frequency?
when Xm-Xs=0
*here we are left with resonance only
how does otosclerosis affect resonant frequency?
raises it to 1200Hz, stiffness increase
how does dislocation of ossicles affect resonant frequency?
stiffness decrease, lowers it to 500Hz
acoustic admittance definition and equation
(Y sub a)
Y sub a=1/Z sub a
it is how easy it is to make particles vibrate–opposite of acoustic impedance
two components of Ya
conductance (G)
susceptance (B)
mass susceptance equation
1/Xm which is to say 1/2piFM
stiffness susceptance equation
1/Xs which is to say 2piF/S
unit used to measure admittance
Siemens
admittance equation
Ya= square root of G^2+(Bs-Bm)^2 which is the same as
Ya=square root of G^2+ (2piF/S - 1/2piFM)^2
equation to express the impedance of a specific medium
Za=square roots (density*elasticity)
**measured in rayls
impedance mismatch
when sound travels between 2 media and some of the sound is transmitted while some is lost
equation for transmission to second medium
T=4r/(1+r)^2
*t=proportion of energy transmitted
r= impedance ratio between the two media
equation for dB lost to transmission mismatch
10log(transmitted (T))/1
mismatch gain from ossicular lever action
2.3dB
mismatch gain from area ratio
26.4dB
mismatch gain from bucking of TM
6dB
total gain from middle ear
34.7dB
psychoacoustics
the study of how people perceive the physical characteristics of sound: “intensity, frequency, and time”
what is the change in loudness we can detect?
1-2dB change
what change in pitch can we detect?
1 micro second change in period
temporal processing
to fully develop the sensation of pitch and loudness, you need to have a few cycles
- at least 200-250msec duration
- at least 1-2 msec gaps
two types of psychoacoustic measures
classical methods *method of limits *method of adjustment *method of constant stimuli forced choice methods
method of limits
used to establish the “limits” of a patient’s hearing threshold
- clinican is in charge
- threshold is 50%
- decision to turn intensity up or down is based on subject’s response
types of methods of limits
- simple up down method
- Hughson-Westlake
- ascending method of limits
- descending method of limits
ascending method of limits
quiet to loud
*threshold is a bit higher (malingering method)
descending method of limits
loud to quiet
- threshold is a bit lower
- *difference is a/b 2-5dB (between ascending and descending?)
ascending-descending method of limits
equal trials of ascending and descending with equal step size (5dB for example)
*not always for thresholds; present one stimulus and compare it to others
Hughson-Westlake
by Carhart and Jerger
*a modification of ascending-descending method
method of adjustment
- pt is in charge
- typically the intesntiy rises smoothly and stays on
- two ways to do this:
- -pt turns a dial to adjust the intensity until threshold is reaches
- -push a button:Bekesy Audiometry
- ——threshold is midpoint between reversal points from increasing to decreasing
affects of guessing on thresholds
increase hits and false positives
*decrease false negative and correct rejections
affects of waiting until absolutely certain on thresholds
hits and false positives decrease
*false negatives and correct rejections increase
latency between stimulus and response
near threshold is longer than above threshold
two-alternative focres-Choice (2AFC)
there are only two alternatives: yes or no
- advantages: can accurately count false positives
- disadvantages: does not control for guessing behavior
two-interval, two-alternative forced-choice (2I-2AFC)
“tell me which interval, the square or the circle, had the sound in it”
- can be modified for 3,4, or as many alternative periods as desired
- advantages: controls for guessing by making everyone guess
- *because making everyone guess it is not reliable to use thresholds of 50%
- **threshold is 1/2 way between chance and certainty
magnitude estimation
asks the pt to assign a number to a stimulus, we use this with CI pts
*how loud is this sound 1 for oft, 2 for medium, 3 for loud
magnitude production
pt is given control of the stimulus, t is instructed to adjust the stimulus until the pt thinks it reaches a predefined criterion
fractionation
the pt makes the stimulus some fraction of its origional quality
*ex: the pt may be askes to make the sound 1/3 as loud, or 2x the pitch
cross-modality matching
using visual representation to measure auditory perception
*ex: after hearing a sound, fill a column of how loud the sound was
hit
response “yes” when signal is present
miss
response “no” when signal is present
false alarm
response “yes” when signal is absent
correct rejection
reponse “no” when signal is absent
what happens when there is a signal plus noise
the signal will be modulated similar to the noise, especially at threshold
gaussian curve has 76% hits, what can you know from this?
has 24% miss, because hits plus misses=100%
*false positives plus correct rejections also equals 100%
d prime
a standard deviation, acts as the ruler meaniing the distances between the noise and noise and signal curves is the number of standard deviations between them
*this is used because there is no numberical scale for the magnitude of the sensory event
how to find d prime
know the percentages of hits, misses, false positives, and correct rejections (convert using z-tables)
*d prime can be validated by changing the instruction/incentives given to the subject
receiver operating curve (ROC)
a plot of the same subjects hits vs false positives at any given value of d prime
- giving various instructions would allow us to develop a receiver operating curve
- we want the patients to be in the top left of the ROC
what does the d prime scale do for us?
it is as close as we can come to a universal scale of human perception
*d prime of 1 for both hearing person and hh person would be the same experience of loudness
outer hair cells voltage
-70mv
inner hair cells voltage
-40mv
scala media voltage
80mv
what does pressure decrease (rarefaction) do the the scala tympani?
pushes scala tympani up and shears stereocilia towards stria vascularis and chanals open and k+ rushes into the cell
spontaneous firing rates
high: 18 spikes/second (60-75% of neurons)
medium: 0.5-18 spikes/second (15-30% of neurons)
low: <0.5 spikes/second ( 10-15% of neurons)
saturation rates for neurons
high and medium spontaneous firing rate saturate at 20-30dB SL, low spontaneous firing rate staturate at 60dB SPL
frequency distribution of auditory nerve
low in the middle (core) and high on the outside of the nerve
physiologic tuning curve
the firing rate of a single neuron
(increase intensity at different frequencies until the neuron fires)
*as a result, we can find the softest frequency at which neuron fires=characteristic frequency/tune
**higher frequencies wont make the neuron fire but low frequencies can at high levels because higher frequencies wont make it as far into the cochlea as lower
frequency/telephone theory
when we have 1000Hz tone, the neuron will fire at 1000x/second (4000 at 4000x/sec, etc.)
*neurons can’t fire faster than 1000-2000x/sec, so this theory does not explain higher frequencies
volley theory
inner hair cell synapses with multiple neurons, this theory says the 1st hair cell will fire to the 1st cycle, the 2nd with the second, and so on, repeating to have enough firings.
*problem here is how would each neuron know which cycle to fire to?
how frequency and intensity is encoded for
neurons tuned to the frequency fire in clusters around when the sine wave reaches 270degrees of phase (rarefaction)
- nothing dictates how often the cell fires, but it will fire in correspondance with rarefactions
- as intensity increases, the timing of the clusters of the neruve firings is still one per msec, but at any given time, more neurons will be firing
phase locking
auditory nerve fibers are able to lock into a phase angle (270 degrees)
period interval histograms
data from single neuron, continuous pure tone is presented, tally the delay b/t firings, the interval between the firings can be compared to the period of the characteristic frequency, provides info about stimulus and which frequency stimulates the neuron but can’t determine the neuron preferred interval and neuron characteristic frequency
post stimulus time histogram
can determine a neuron’s specific characteristic frequency, single neuron and clicks are presented, neural responses are measured across time, the time of each response is enter into hist. and the interval between the firings can be compared to the period of the characteristic frequency, 10 clicks are presented, the firing to the signal and subsequent ringing on basilar membrane makes it good for low tones, number of firings at each time interval are marked and this shows the characteristic frequency
compound action potential
more neurons fire for loud sounds than soft
how does masking work?
high frequency sounds can be masked out by louder lower frequency sounds
- some of the neurons that would normally phase lock and encode the softer signal to make it audible are bust responding to the more intense signal
- *aka upward spread of masking
how does masking low frequencies work?
need to be masked by close frequency so there is overlap on basilar membrane (this is in terms of higher frequency masking a lower frequency)
Minimal audible field
MAF= created by finding the thresholds, then placing the sound level meter where pt was and seeing what SPL was audible, all subjects are averaged to find MAF
- MAF is the minimum SPL audible to normal hearing ear at each frequency
- limitation: no subject is presnet so the affect of the subjects body on the sound field is removed
Minimal audible pressure
MAP= audible SPL with inserts and probe mic in ear canal or coupler
*with coupler is MAP-C; coupler used is 2cc or zwislocki
MAP vs MAF
MAF does not account for the signal absorbed or reflected by the subject body
*earphones can move and cause noise to interfere with thresholds
MAP vs MAP-c
MAP measurements already account for he resonance of the ear
binaural advantage
2-3dB increase on average
- if ears were completely the same, you would see 3dB increase because of the doubling in pressure
- *MAF is both ears, MAP is one ear
is there a difference between 0dB HL with different transducers?
yes, in SPL they are different, but perception is the same
*inserts have low MAP because of occlusion and the fact that they remove the resonance of the ear canal (as compared to circumaural and supra-aural
transfer function of the ear
tells us how frequencies would be altered as they are transmitted through the system
- not all frequencies pass through the outer and middle ear equally well
- *outer ear resonance and middle ear mass and stiffness
- **we can predict that at 40dB SPL, 2000Hz tone will be louder than 250Hz because the ear canal and middle ear amplifies it more
active mechanism
cochlear amplifier
- movement of outer hair cells enhances the vibration of the basilar membrane
- enhances the basilar membrane, but to a limit
- *40-60dB gain but amplifies the soft signals while not amplifying the loud ones
- movement of the basilar membrane is enhanced for very low-intensity sounds, this permits the rapid increase in loudness levels for the lowest level sounds, and agrees fairly well with the growth of loudness curve
basilar membrane activity
as a pure tone signal grows louder, the traveling wave becomes greater (leads to more neurons stimulated and more firings going to the brain)
effect of temporal integration on threshold
as tones decrease in duration below about 200msec, thresholds get worse
- 200msec in the auditory system is “infinitely long” meaning a length above this will not affect perception
- *below 200msec, a 10 fold change in duration changes threshold by 10dB
- **doubling duration is change of 3dB
- ***different frequencies are affected differently
how are different frequencies affected differently by temporal change
the period length is the amount of opportunities for the neuron to fire in that time frame
why does threshold become better above 200msec?
enough cycles for the brain to detect
what happens when tone pips and clicks are presented at a high rate?
the energy summates, the sound is perceived as louder and the threshold for hearing is lower
difference limen
the difference threshold, or just noticeable difference meaning the smallest change we are able to detect 50% of the time (or 75% on 2-interval forced choice)
weber’s law
for all senses, we detect a relative or proportional or % change
- **the ability to detect a change is proportional to the size of the original stimulus
- ***change in stimulus over stimulus
what is meant by wide band noise being a “near miss” to weber’s law?
most frequencies match, but below 20dB sensation level, it takes a greater change in sound level to detect a loudness difference
***for pure tones, the DL continues to improve as sound intensity increases (2dB difference at soft levels and 1dB at loud)
phon
loudness unit used to measure equal loudness; equal loudness to a 1000Hz signal
- phon curves do not represent a doubling in loudness (40phons is not 2x as loound as 20 phones)
- doubling intensity does not double loudness
at which frequencies is loudness growth faster
at lower frequencies is faster than at higher
dynamic range
the range from audibility to uncomfortably loud
*normal is 70-100dB
dB A
represents the 40 phon curve
*used for industrial measurements
dB B
represents the 70 phon curve
dB C
represents the 100 phon curve
sone scale
40dB SPL at 1000Hz
*all values on the 40 phone curve would be considered as 1 sone because they are all equal in loudness
( a sound that is perceptually twice as loud as 40dB SPL at 1000Hz is 2 sones
loudness growth
doubling of loudness with 10dB growth at lower levels and 6dB growth with doubling of loudness at higher levels due to the active mechanism increasing the softer signals by 40-60dB, but does not affect the louder sounds
*change occurs around 40dB SPL
steven’s law–the sone sacle
L=k*P to the power of e
L=loudness level in sones
K=constant that varies with frequency (0.0105 for 1000Hz)
P= the actual sound pressure in micro pascals
e= 0.6 when measuring the sound in micro pascals and consider 10dB double loudness, not 6dB
similar calculation to steven’s law
L=10 to the power of [0.03*(dB SPL-40)]
loudness adaptation
if a sound remains on for a long period of time, that is, a minute or more, and stays the same intensity and frequency, it may begin to be perceived as less intense
(aka auditory adaptation)
***normal hearers adapt faster to low intensities and high intensities
tone decay
similar concept to loudness adaptation, but a signal that is at first audible fades away to inaudible
temporary threshold shift
occurs because of prior exposure to intense sounds
resulting in reduction of loudness perception
*excessive potassium influx cause cell to lose ability to do its function for a period of time
permanent threshold shift
aka noise-induced hearing loss happens with repeated or prolonged noise exposure
limits of tonal perception
20-20,000Hz
what is pitch perception dependent on?
intensity and duration of signal
how is pitch perception affected by intensity
with an increase in intensity:
- frequencies under 1000Hz are perceived as lower in pitch
- frequencies between 1000-2000Hz are perceived as the same pitch as they were
- frequencies above 2000Hz are perceived as higher in pitch
how is pitch perception affected by duration
brief tones do not have full tonality (due to frequency splatter)
- the longer the signal, the clearer the tone perception
- need more cycles to be perceived with tonality at higher frequencies because phase locking falls apart at higher frequencies and brain must go through the more random firing to decide the frequency
Difference Limen (DLf)
the smallest pitch change that the ear can detect 50% of the time
*remember: weber’s law states that the ability to detect a change is proportional to size of the original stimulus
place theory
the traveling wave must peak at a different place on the basilar membrane for tones to be perceived as different
frequency modulation (FM) frequency difference limen task
this method is affected by the modulation rate
- how fast can you change between frequencies in 1 second will affect the listener’s perception
- **a way to measure the DLf
paired–comparison method
used more frequently
- amplitude is increased gradually
- **way to measure the DLf
what makes the DLf better?
higher signal intensity
Mel scale
pitching scale
- one Mel (melody) is defined as a pitch that is 0.001 of the pitch of a 1000Hz tone at 40 dB SPL (40 phons)
- *the pitch of a 1000Hz tone at 40dB SPL is 1000Mels, 50 Mels is half the pitch of 1000Mels and 2000Mels is 2x the pitch
- **nonlineers meaning doubling the frequency does not double the pitch
what happens when two tones are presented to the same ear (or both simultaneously) and they are very close in pitch
an intensity modulation resulting in beats
*as the difference between the tones increases the beating becomes faster, and at some point the perception changes to a “rough” tone, then with more separation a distinct third tone is perceived
simple difference tone or quadratic difference tone
when two different tones are presented together and a distinct third tone is heard
F2-F1
cubic difference tone
2F1-F2
aural harmonic distortion
occurs at multiples of the original frequency
- ex a 1000Hz tone will have harmonics at 2000, 3000, 4000, etc.
- shorthand is 2F1, 3F1, etc.
- only occurs when the ear is stimulated at very loud levels
combination tones
occur at moderate loudness levels
- includes summation tones and difference tones
- simple summation tone: occurs at F1+F2, but many other summation tones can occur
missing fundamental frequency
multiple frequencies with the same spacing will create the perception of a frequency at the spacing frequency (how we get the fundamental frequency on the telephone)
OAE testing
evaluates whether the nonlineraities (distortions from the active mechanism of the middle ear) are present, particularly the cubic difference tone
*the presence of this tone is a sign of healthy outer hair cell function
