Download Distortion product otoacoustic emissions: Introduction

Distortion product otoacoustic
emissions: Introduction
Michael P. Gorga, Ph.D.
Boys Town National Research
Hospital
Work supported by the NIH
Collaborators on BTNRH OAE
Projects
• Stephen Neely
• Kathy Beauchaine
• Darcia Dierking
• Tricia Dorn
• Cassie Garner
• Brenda Hoover
• Debra Hussain
• Jan Kaminski
• Walt Jesteadt
• Tiffany Johnson
• Doug Keefe
• Dawn Konrad-Martin
• Danielle Montoya
• Jo Peters
• Beth Prieve
• Joelle Redner
• Laura Schulte
• Brenda Starnes
• Alicia Schmiedt
• Lisa Stover
Principles behind the use of
OAEs to identify hearing loss
•normal cochlea behaves nonlinearly
•source of nonlinearity is the OHC system
•OHCs are physiologically vulnerable
•OAEs are byproducts of normal nonlinear
function
•loss of OAEs indicates damage to the
OHCs
1
The clinical Link
•OHC damage is closely linked to hearing
loss, at least for losses up to about 50-60
dB
•loss of OAEs indicates OHC damage,
which in turn, indicates the presence of
hearing loss
Stimuli for eliciting DPOAEs
•two primary tones, f1 and f2
•f2 = 1.22(f1) (same as f2/f1 = 1.22)
•primary levels may range from 0 to 85
dB SPL
•moderate primary levels are in most
common clinical use
•primary levels may be equal or L1 may
be greater than L2
•primary-level differences should
increase as overall level decreases
Distortion Product Otoacoustic
Emission
• acoustic response measured using microphone in the
sealed ear canal
• evoked using two-tone stimulation (f1 and f2; f1 < f2)
• response is due to intermodulation distortion in the basilarmembrane response
• many DPs are generated, but response typically is
measured at the frequency equal to 2f 1-f2
2
Measuring DPOAEs
•many distortion products are produced
but response typically is measured at a
frequency equal to 2f1-f2 because it is
the largest one in mammals
•noise typically is estimated as the
average level in several frequency bins
above and below the 2f1-f2 bin.
•DPOAE-to-noise ratio (SNR) is
estimated as the dB difference between
energy at 2f1-f2 and energy in adjacent
noise bins
DPOAE Measurements
•DPGrams - plots of DPOAE level as a
function of either f2 frequency or the
geometric mean frequency, which is
defined as the square root of (f2 x f1),
while primary levels are held constant.
•DP Input/Output (I/O) functions - plots
of DPOAE level as a function of primary
level while primary frequencies are held
constant.
3
Measurement-Based Stopping
Rules
•stop test if noise level is reduced to
some criterion level, related to the level
at which system distortion occurs
•stop test if SNR exceeds some criteria
•stop test if response level exceeds
some criteria
•stop test after some amount of test time,
even if measurement-based criteria are
not met.
Why Measurement-Based
Stopping Rules?
•Increases test efficiency - don’
t waste time
•measurements are terminated if high SNR is
observed, meaning a response is present
•measurements are terminated if low noise is
achieved, meaning that, if a response was
present, it should have already been
measured
•measurements are terminated after some
time limit, preventing the test from continuing
indefinitely.
4
Distortion product otoacoustic
emissions in relation to
hearing loss
Data From Subjects with
Hearing Loss
•DPgrams tend to mimic the audiogram. That
is, there is reduced output (for fixed primary
levels) at those f2 frequencies at which
hearing loss exists
•I/O functions also reflect the pattern of
hearing loss. That is, there is less output
over most of the range of levels for
frequencies at which hearing is impaired.
Note: high level responses may be more
normal, depending on magnitude of loss
5
from Kemp et al. (1986),
Scand. Audiol. 25 (Suppl.),
71-82
Next Slide
Kemp et al. (1986)
•Top panel: Data from normal ears
•Middle panel: DPgrams from three ears
with hearing loss
•Bottom panel: Audiograms from the same
three ears with hearing loss
•Note: Frequency is represented on a
linear scale
6
from Martin et al. (1990), Ann.
Otol. Rhinol.Laryngol. 99
(Suppl. 147), 29-44
Next 3 data slides
Martin et al. (1990)
•Top row: Audiograms (separate panels for each
ear) and DPgrams (different symbols for each
ear)
•Bottom row: DP I/O functions (different symbols
for each ear)
•Note: The frequency scale in the audiogram
goes from 0.125 to 8 kHz, whereas the DPgram
goes from 1 to 10 kHz. Both scales are
logarithmic
7
Summary of Case Studies
•DPgrams follow the audiogram, showing
responses for frequencies where hearing
is normal and reduced or absent
responses when hearing loss exists.
•I/O functions also are consistent with
audiometric status.
8
Case Studies versus Group
Results
•Case studies are informative, but what is
needed are data from large samples of
normal and hearing-impaired subjects
•Large sample studies allow for quantitative
analyses from which it will be possible to
describe how DPOAE tests (or any test,
for that matter) perform under clinical
conditions
Factors affecting DPOAE test
performance
•f2 frequency (Gorga et al., 1993, 180
subjects)
•primary levels (Stover et al., 1996, 210
subjects)
•magnitude of hearing loss (Gorga et al.,
1997, 806 subjects)
Effects of f2 Frequency
From Gorga et al. (1993), JASA
93, 2050-2060
9
ROC Curves
•Hit rate as a function of false alarm rate
•Comparisons are made when f2 =
audiometric frequency
•Parameter is f2 frequency
•In these coordinates, chance
performance occurs when ROC curve
has a slope of one (line falls on positive
diagonal).
•Perfect performance occurs when hit
rate = 100% and false alarm rate = 0%.
Frequency Effects
•Performance at 500 Hz is near chance
•Performance improves as f2 increases
•Best performance observed at 4 kHz
•Slight drop in performance when f2 = 8
kHz.
10
Reasons for Frequency Effects
•noise decreases as frequency increases
•forward (and perhaps reverse) middle ear
energy transmission is more efficient for
mid to high frequencies compared to lower
frequencies
•cochlear distortion maybe greater for
higher frequencies compared to low
frequencies
Low-Frequency Limits of
DPOAE Measurements
•primary source of noise in DPOAE
measurements is breathing and
movement noise, which are dominated
by low-frequency energy
•noise increases as frequency
decreases, thus making it harder to
reliably measure a response at lower
frequencies
•noise problems are compounded by
measuring responses at 2f1-f2
The Problem of Measuring
Responses at 2f1-f2
•DPOAEs are generated at the f2 place
•cochlear status at the f2 place is being
predicted from DPOAE measurements
•predictions are based on measurements at
2f1-f2, which is about 1/2 octave below f2,
where noise levels are higher, making
measurements less reliable
11
Stimulus and Response
Representations
•Top: Stimuli and response. Note that 2f1f2 is below f1
•Bottom: Idealized representation of stimuli
and response along the basilar
membrane.
Interactions Between Frequency
of Interest (f2) and the Frequency
of Measurement (2f1-f2)
•noise levels reach asymptotic low levels
for f2’
s at 4 kHz. Thus, it matters little
that 2f1-f2, the frequency of
measurement, is about 1/2 octave
below f2, the frequency of interest
•interaction has a significant negative
impact for f2’
s at and below 4 kHz,
because 2f1-f2 falls in frequency regions
for which noise levels increase
12
Performance at 8 kHz
•While noise is the major source of reduced
test performance for lower frequencies,
noise levels are very low at 8 kHz
•Thus, poorer performance at 8 kHz cannot
be due to noise
•Poorer performance may relate to the need
to drive the loudspeakers with a greater
voltage in order to get target primary levels.
This high voltage may result in an increase
in system distortion, resulting in poorer
performance
Primary Level Effects
•Should we use primary levels that result
in the largest responses from subjects
with normal hearing - that would be the
highest possible level
•Should we use primary levels close to
threshold - that would require several
measurements under conditions of poor
SNR
•Should we use primary levels that result
in the greatest separation between the
distributions of responses from normal
and impaired ears
Effects of Primary Level on
DPOAE Test Performance
From Stover et al. (1996), JASA
100, 956-967
Next 6 data slides
13
I/O Functions to DPgrams
•I/O functions plot DPOAE amplitude vs.
L2
•Obtain DPOAE I/O functions for several
f2 frequencies
•From each I/O function, note the
DPOAE amplitude when L2 is held
constant
•DPgrans are plots of these amplitudes
as a function of frequency
14
DPgrams and Audiograms in
Normal ears
•Audiogram –bottom row, middle panel
•DPgrams, constructed from I/O functions,
for five different L2 levels
•High-level –bottom left panel
•Low-level –bottom right panel
•Moderate levels –top row of panels
Results in Normal Ears
•Normal ear produces response for most
frequencies and most L2 levels
•Low-level stimuli sometimes do not
produce responses in ears with normal
hearing.
15
I/O functions in an ear with
hearing loss
•Noise levels caused variability in I/O
functions at lower f2 frequencies
•Normal appearing I/O functions at 1, 1.4,
and 2 kHz
•“
Abnormal”I/O functions at 2.8, 2, and 4
kHz
•Probably normal I/O function at 8 kHz
DPgrams and Audiograms in
an Ear with Hearing Loss
•Audiogram - bottom row, middle panel
•Abnormal response at high levels, but only for 4
kHz (lower left panel)
•Abrnormal responses for moderate level
primaries at frequencies for which hearing loss
exists (top row of panels)
•Abnormal response at 8 kHz for low-level stimuli,
even though hearing was normal at this
frequency
16
Test Performance Vs. L2
•Area under the ROC curve is an estimate of
test performance
•Test performance is defined as the test’
s
ability to correctly identify both normal and
impaired ears
•Areas close to 0.5 Represent chance
performance
•Areas close to 1.0 represent perfect
performance
•Each function represents data for a different
frequency
17
Effects of Primary Level
•At all f2 frequencies, test performance
increases as L2 increases
•An maximum asymptotic value is achieved
at moderate L2 levels
•Performance decreases slightly at higher
L2 levels
Reasons for Primary Level
Effects
•normal ears may not produce a response
at low levels - drives up the false positive
rate
•impaired ears may produce a response at
high levels - drives up the false negative
rate
•moderate levels should minimize errors
Laboratory vs. Clinical
Observations
•Test performance is determined most
by f2 frequency. Do the effects of f2
frequency, observed under laboratory
conditions, hold when data are obtained
under routine clinical conditions
•Will the optimal primary levels under
laboratory conditions work well in the
clinic
18
Large Scale Study in the
Clinic
•1257 ears of patients seen through the
audiology clinic
•subjects’
ages covered the life span
•all subjects had normal tympanograms on
the day of the DPOAE test
•audiograms were available for all subjects
•65/55 dB SPL primaries were used, given
the results of the primary level studies
Effects of f2 Frequency under
Clinical Conditions
From Gorga et al. (1997), Ear &
Hearing 18, 440-455
ROC Curves
•Plots of hit rate vs. false alarm rate
•Triangles: SNR was used
•Circles: DPOAE level was used
•Each panel shows data for a different f2
•ROC curve areas are given inside each
panel
19
Clinical Observations
•results under clinical conditions are
virtually identical to those seen in the
laboratory
•test performance is best for frequencies of
4 and 6 kHz
•test performance is poorer as f2 decreases
and for 8 kHz
Summary
•DPOAEs accurately identify auditory status
at mid and high frequencies
•DPOAEs are less accurate for frequencies
<1.5 kHz, due primarily to noise levels
•DPOAEs are more accurate for moderate
level primaries
•DPOAEs will miss some ears with mild
hearing loss
•DPOAEs will incorrectly label some ears
with normal hearing as impaired
20
Establishing DPOAE Criteria
for Use in the Clinic
Gorga et al. (1996) JASA 100,
968-977
Gorga et al., (1997) E&H 18, 440455
Shortcomings of Common
Approaches for Selecting
DPOAE Test Criteria
•Data from normal-hearing subjects can be used
to estimate ONLY the false-positive rate (a
problem not only for SNR)
•a priori SNR criteria, such as 3, 6 or 9 dB
SNRs, do NOT result in a 100% hit rate or a 0%
false-alarm rate
Equal SNRs do not = the
Same Auditory Status
•DPOAE = 5 dB SPL at 4 kHz
•Noise = -4 dB SPL at 4 kHz
•SNR = 9 dB, cochlea probably normal
•DPOAE = -15 dB SPL at 4 kHz
•Noise = -24 dB SPL at 4 kHz
•SNR = 9 dB, cochlea probably abnormal
•SNR alone would have misdiagnosed the
second case as normal hearing
21
Another Problem: Response
Distributions Overlap
•There are no DPOAE criteria that
perfectly separate the responses
observed in normal ears from those
seen in impaired ears.
•Errors are inevitable. The question is,
“
which error is more important, falsepositive or false-negative errors”
.
Which Error is More Important
•Prevalence may be important in
choosing which error to control
•If the incidence of hearing loss is low in
the target population, one might want to
minimize the false-positive errors
•If the incidence is high in the target
population, then one might want to
minimize the false-negative errors.
Cumulative Distributions (CD)
•CDs are the proportion of time responses occur that
are ≤some criterion value as a function of that value
•CDs are another way of plotting a normal distribution.
The same data that result in a bell-shaped normal
distribution result in a sigmoidal (S) shaped CD. CDs
are just a different way of looking at the same data
•CDs of responses from both normal and impaired ears
are needed whenever the distributions of normal and
impaired responses overlap
22
Possible DPOAE criteria that
can be used in the clinic
•DPOAE Level
•DPOAE SNR
•DPOAE Threshold
•Multivariate Scores
•Other, as yet, undetermined DPOAE
measure, such as latency or slope of
the I/O function
Developing an Approach for Use in the
Clinic (Gorga et al., 1996, 1997)
•We need CDs of the measurement variable of interest
(i.e., DPOAE level or SNR).
•CDs from normal-hearing ears can be used to
determine criteria associated with specific falsepositive rates
•CDs from impaired ears can be used to determine
criteria associated with specific hit rates
Selecting a Hit Rate from CDs
•One approach for selecting a criterion DPOAE
value is to first decide on an acceptable hit rate
or test sensitivity
•Draw a horizontal line at that hit rate until it
intersects the distribution of responses from
impaired ears
•Drop a vertical line to the X-axis to find the
criterion value that provides that hit rate
23
Selecting a False-Alarm Rate
•Decide on an acceptable false-positive rate
•Draw a horizontal line at the false-positive rate
until it intersects the distribution of responses
from normal ears
•Draw a vertical line from this intersection to the
X axis to find the criterion DPOAE value
associated with that false-alarm rate
Cumulative Distributions in
Normal and Impaired Ears
Note: As examples, criteria are
selected that resulted in a 95% hit
rate (impaired CD) and a 5% false
alarm rate (normal CD)
24
Figure showing DPOAE
Levels for Fixed False Alarm
and Hit Rates
•DPOAE level as a function of f2
•Data from normal (left panel) and
impaired (right panel) ears are shown
•Parameter is percentage, from 5th to
95th percentiles
•Filled symbols represent the DPOAE
levels at the median (50th) percentile
Evidence of Overlap Between
Normal and Impaired
Responses
•No criterion can be selected for which the hit
rate is 100% AND the false alarm rate is 0%.
All of the functions in the right panel are not
below all of the functions in the left panel.
•Some impaired ears produce bigger responses
(or lower thresholds) than some normal ears
•Or, stated differently, some normal ears
produce smaller responses (or higher
thresholds) than some impaired ears
25
Constructing a Useful Clinical Form
(Gorga et al.,1997, 2002)
•Select 1 or 2 hit rates (say 90th & 95th %) and
find the DPOAE criteria associated with them
•Select 1 or 2 false-alarm rates (say, 5th & 10th
%) and find the DPOAE criteria associated with
them
•Plot these values (DPOAE criteria vs. f2) to
create a form for clinical use
Basis for Developing a Clinical
Form
•Right: Schematic showing overlap between
DPOAE levels from normal and impaired ears
•Left: top line = 95th percentile (hit rate =
95%) from impaired distribution, second line =
90th percentile from impaired distribution (hit
rate = 90%), third line = 10th percentile from
normal distribution (false-alarm rate = 10%),
bottom line = 5th percentile from normal
distribution (false-alarm rate = 5%)
26
Interpreting DPOAE Data,
Using the Left Panel of the
Previous Figure
•Responses above highest values from impaired CDs
would be consistent with normal hearing because few
impaired ears produced responses this big or bigger
•Responses below lowest values from normal CDs
would be consistent with hearing loss because few
normal ears produced responses this small or smaller
•Diagnosis is uncertain for responses between these
values (i.e., in shaded regions), where normal and
impaired responses overlap
Large Sample Study
figure and data from Gorga et al. (1997, E&H)
and Gorga et al. (2002) in Robinette and
Glattke, 2nd Ed.
•Data from 1257 normal and impaired ears
•L1/L2 = 65/55 dB SPL
•All data collected under clinical conditions
•Measurement-based stopping rules were
used
BTNRH Clinical Form
NOTE: Baljit Rehal, Au.D. was
instrumental in developing this form
27
Caveats when using this form
• SNR should be ≥6 dB IF noise floor is not below the lower limit
of graph in order to use this form to help interpret responses
• Large DPOAE levels cannot be plotted on this form if DPOAE ≈
noise floor (i.e., SNR≈0 dB); such “
responses”are
uninterpretable because they could be just noise
• If noise is reduced below lower limits of graph AND response is
not above the noise floor (SNR=0 dB), the results are
interpretable (i.e., consistent with hearing loss) because the
reason no response was observed was because the response
was so small, not because the noise was too high
• Diagnosis is uncertain for responses in shaded area (SNR≥6
dB but responses from normal and impaired ears overlap).
Interpreting Responses in the
Shaded Areas
•There should be a minimum SNR of 6
dB
•Between 90th (impaired distributions and
5th (normal distributions) percentiles,
responses fall in the region of
uncertainty because there is overlap in
responses from normal and impaired
ears
28
Five Case Studies, in which
Clinical Form was Used to Assist
in Interpretation
First step in interpreting results is to
determine if DPOAE level was reliably
measured. SNR helps to determine that.
A related issue is to determine whether
the noise floor was sufficiently reduced.
Case #1
Frequency
750
1000
1500
2000
3000
4000
6000
8000
DPOAE
7
8
6
3
1
2
3
-5
Noise
- 8
-10
-11
-13
-15
-20
-21
-20
Signal/Noise
15
18
17
16
16
22
24
15
29
Case 1: Results Consistent with
Normal Hearing
•Low noise levels even for lower f2’
s
•Large DPOAEs
•Positive SNR at all f2’
s
•Levels above 90th percentile for
impaired ears
•Results consistent with normal hearing
because few impaired ears produce
such large responses
Case #2
30
Frequency
750
1000
1500
2000
3000
4000
6000
8000
DPOAE
7
8
5
0
1
0
1
-5
Noise
6
8
3
-1
2
0
0
-7
Signal/Noise
1
0
2
1
-1
0
1
2
Case #2: High Noise Levels =
Uninterpretable Responses
•“
Large”DPOAEs
•High noise levels
•Low SNR
•Results are uninterpretable because
“
large”DPOAEs may be nothing more
than noise
•Note that the levels were the same as for
Case #1
31
Case #3
Frequency
750
1000
1500
2000
3000
4000
6000
8000
DPOAE
-15
-14
-16
-18
-17
-18
-20
-26
Noise
-16
-15
-17
-17
-17
-20
-20
-25
Signal/Noise
1
1
1
1
0
2
0
-1
32
Case #3: Low SNR & Low Noise
Levels can be Interpreted
•DPOAEs below the lower limits of graph
•Noise levels also are low
•Low SNR (i.e., DPOAE level was not measured
reliably above the noise floor)
•Results are consistent with hearing loss because
the reason a response was not measured was
NOT due to high levels of noise, but to low level of
response.
Case #4
Frequency
750
1000
1500
2000
3000
4000
6000
8000
DPOAE
0
0
-5
-6
-8
-6
-7
-15
Noise
-10
-11
-14
-14
-19
-20
-22
-25
Signal/Noise
10
11
9
8
11
14
15
10
33
Case #4: DPOAEs in the region
of uncertainty
•DPOAE levels in shaded region
•Noise levels well below DPOAE levels
•Positive SNR, meaning DPOAEs were
measured reliably
•Results cannot be assigned to normal or
impaired distribution
Responses between 90th (Impaired)
and 5th (Normal) Percentiles (Gorga et
al., 2002)
•This is the region where overlap occurs between the
responses produced by normal and impaired ears.
One might conclude that these responses are
completely uninterpretable
•If SNR ≥6 dB, we can exploit the relation between
audiometric threshold and DPOAE level to help
interpret the response
34
Audiometric Threshold vs.
DPOAE Level
•Audiometric threshold (dB HL) as a
function of DPOAE level (dB SPL)
•Data for a different f2 shown in each panel
•Solid line = 50th percentile (median)
•Shaded areas = interquartile range (25th to
75th percentile)
Audiometric Threshold vs.
DPOAE Level
•Audiometric threshold decreases as DPOAE level
increases
•Although variable (note that the shaded area only
covers the middle 50% of the distribution at each
audiometric threshold), relation exists for audiometric
thresholds from -5 to about 50-60 dB HL
•No relation above 55 dB HL, related to the range of
levels over which outer hair cells operate
35
Caveats For This Form
•The SNR should be ≥6 dB
•The shaded area covers only the 25th to
the 75th percentile
•Thus, there are still cases when
interpretations will be wrong
•However, using this form provides
limited but still useful information for
interpretation, especially when no other
data are available to assign a response
to either normal or impaired groups
Interpreting Data in the
Region of Uncertainty
•DPOAE levels reliably measured
•All DPOAEs are in region of uncertainty; thus, they
cannot be assigned to normal or impaired distributions
•Given the measured levels, one would anticipate that
these responses were coming from an ear with either
normal hearing or mild hearing loss (see previous
figure). It would be less likely that these responses
were coming from an ear with moderate, severe or
profound hearing loss.
Case #5
36
Frequency
750
1000
1500
2000
3000
4000
6000
8000
DPOAE
-2
0
-3
-5
-7
-6
-7
-15
Noise
-1
-2
-4
-5
-8
-5
-7
-16
Signal/Noise
-1
2
1
0
1
-1
0
1
Case #5: Uninterpretable
DPOAEs in Region of Uncertainty
•DPOAEs in shaded region
•Noise levels = DPOAE level (SNR ≈0)
•DPOAEs, therefore, are not reliable
•Results cannot be interpreted (cannot use
either form) because measured “
responses”
may be just noise, but this cannot be known
37
Univariate vs. Multivariate
Analyses
•Univariate approach compares data
from one measurement (say DPOAE &
noise level at one f2) to predict cochlear
status at the same frequency.
•Multivariate analyses use data from
many variables (in our case, DPOAE
level and noise for many f2’
s) to predict
cochlear status at a single frequency.
What Do Multivariate
Analyses Do?
•Use many variables as inputs to generate a
single dimensionless number
•select variables and coefficients that result in
the greatest separation between the means of
two distributions of the new dimensionless
variable
•Select variables and coefficients that minimize
the variance of each distribution
One Kind of Multivariate
Analysis
Discriminant Analysis
38
Developing Multivariate
Solutions
•Because many variables are being used,
the solutions can be irregular and may not
generalize to a new set of data
•Multivariate solutions should be validated
on an independent set of data
Validating Multivariate Analyses
(Dorn et al., 1999)
•Obtained large data set
•randomly divided data set in half
•use the first half to develop (train) the algorithm
•do not change the training algorithm
•apply training algorithm to the other half of the
data set
39
Relative Operating Characteristic
Curve Areas (AROC)
•AROCs can be used to describe test
performance for dichotomous clinical decisions
(i.e., normal versus impaired hearing)
•AROCs range from 0.5 (chance performance)
to 1.0 (perfect performance)
•No audiological tests have AROCs equaling
1.0.
Univariate vs. Multivariate
Results
•Multivariate solutions provide better test
performance than univariate analyses
•greatest differences between univariate
and multivariate approaches occurs in
the lower frequencies
•Multivariate solutions do nearly as well
on validation set as they did on training
set. Thus, the solutions appear to be
robust
•Validation from studies by other
investigators would be useful
40
Problems with Validation in
Original Work
•Both ears of many subjects were tested
•Ears were randomly assigned to either training or
validation sets
•The two ears of the same subject are not independent
•A completely independent data set are needed to
evaluate the generalizability of the multivariate
solutions
A Better Validation of Multivariate
Analyses (Gorga et al., 2005)
•An entirely new set of subjects:
–345 ears of 187 subjects, 2 to 86 years of age
–No middle-ear dysfunction
–Pure-tone audiograms measured for each subject
•DPOAE Stimuli:
–f2 = 0.75 to 8 kHz, half-octave steps
–f2/f1 = 1.22
–L1 = 65 dB SPL; L2 = 55 dB SPL
•Previously described multivariate solution, without
modification, were applied to these new data.
•Clinical decision theory (AROCs) used to assess
test performance
41
SNR & DPOAE Level Versus
Multivariate Solution
•AROCs are larger for SNR compared to
DPOAE level at lowest frequency, while
AROCs are larger for DPOAE level at most
mid and high frequencies
•AROCs for multivariate analyses exceed
those for both DPOAE level and SNR, with
the exception of 4 kHz, a frequency for which
areas are about the same.
Conclusions
•Previously described multivariate
solutions were robust and generalized
to an entirely new set of data.
•Improved DPOAE test performance can
be achieved by using the multivariate
solutions.
•The improved test performance does
not require any additional test time.
Case Studies
Comparing…
•Pure tone audiograms
•DP-Level form (univariate analysis)
•P(N) form (multivariate analysis)
•NOTE: Probability of normal (P(N)) is derived
from the dimensionless number generated by
the multivariate analysis
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Normal hearing subjects with high P(N)
Hearing impaired subjects with low P(N)
Hearing Impaired Subjects with Flat and Sloping Losses
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Test performance is not perfect:
Example of a false negative
Test performance is not
perfect: Example of a False
Positive
Summary
•DPOAEs do not perform perfectly
•Test performance can be improved by
using multivariate analyses
•Multivariate solutions are robust and
appear to generalize
•Even with these improvements, perfect
performance is never achieved
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Bad News - Good News
•The bad news is that errors in diagnoses are
inevitable when DPOAEs are used to identify
hearing loss.
•This is true for other tests, not just DPOAE
tests.
•The good news is that, when auditory status
is uncertain, it is more likely that we are
confusing normal or mild hearing losses or
mild and moderate hearing losses. It is much
less likely that we are confusing normal
hearing with moderate or greater losses.
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