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Changes the shape of the hair cell. Changes in trans-membrane voltage cause the hair cells to move which creates a change in the membrane protein prestin.
Acoustic input sets up traveling wave on basilar membrane. Reverse traveling wave is created by outer hair cells and resulting sound pressure is measured in ear canal. These are the by-product of the cochlear amplifier and can indirectly tell us about the amplifier's functioning.
4 types of OAEs
1. DPOAEs (C)
2. TEOAEs/CEOAEs (B) - transient or click evoked
3. SFOAEs (D) - stimulus frequency
4. SOAE (A) - spontaneous
Reflection shows irregularities. The TEOAE hits an irregularity in the cochlea to create a bumpier line.
F1 and F2 overlap to create a third tone that is caused by distortion. It is at a different frequency than F1 and F2.
DPOAE fine structure
Interaction between distortion and reflection. Fine structure are peaks and valleys and may affect your readout. Some screeners can change the F1 and F2 slightly to see if they get a better response.
Each tone is presented through its own loudspeaker in order to avoid extra distortion.
OAEs and the audiogram
•Thresholds ≤15 dB HL: present with normal amplitude
•Thresholds from 20-40 dB HL: present but abnormal amplitude
•Thresholds >40 dB HL: absent
•These rules of thumb apply when the loss is primarily sensory in nature and there is no conductive component
The first OAE probes were assembled from hearing aid parts and epoxy resin
Kemp's discovery of OAEs
•Healthy ears generate measurable sound in response to clicks - frequency dispersion (high frequency come back first then lower frequencies)
•The response shows frequency dispersion and nonlinear amplitude growth (more gain for loud sounds and less gain for soft sounds)
-Suggested cochlear origin
•Responses were absent in a coupler and ears with hearing loss
Suggested potential clinical utility
•Newborn hearing screening - used with or instead of ABR results to screen for hearing loss
•Cross-check of audiologic results (e.g., pediatrics, non-organic hearing loss) - good objective measure to compare with behavioral results
•Assessment of peripheral function for different pathologies (e.g., tinnitus, APD, ISSNHL, etc.)
•Diagnosing ANSD - detecting whether OHCs are present and healthy
•Monitoring ototoxicity and NIHL - can detect hearing loss before it shows up on the audiogram
Time after birth
Fluid may still be in the ear from birth.
Bigger OAEs in beginning of life but get smaller with age
Women have bigger TEOAEs and SOAEs
You need a quiet environment to obtain OAEs
Analysis of OAEs
Present and normal
Consistent with functional outer hair cells. Consistent with thresholds better than 25-30 dB HL at frequencies tested. Is not synonymous with normal hearing: could have mild hearing loss.
Present but abnormal
May be consistent with subclinical hearing loss at frequencies tested (normal audio, absent OAEs). May be consistent with mild sensory loss at frequencies tested. Further investigation warranted (follow up with audio or ABR).
Consistent with outer hair cell dysfunction. Consistent with sensory loss of at least 30-40 dB HL at frequencies tested (could be greater). Assuming normal outer/middle ear involvement.
DPOAEs v TEOAEs
Both are effective hearing screening tools for NBHS. Norton et al. (2000) demonstrated equivalent identification of hearing loss. Each OAE type may be differentially sensitive to pathology that affects cochlear amplification vs. nonlinearity (Shera & Abdala, 2012). Aspirin affects TEOAEs but not DPOAEs.
•80-μs clicks (pre-neural response therefore no adaptation at higher click rates)
•Stimulus level ~80 dB peak SPL
•Nonlinear protocol to cancel stimulus artifact: Three clicks of equal amplitude and fourth click at 3x amplitude in opposite polarity.
•260 sweeps: 260 x 4 clicks
Analyzed from 0-20 ms. First 2.5 ms zeroed-out to reduce stimulus artifact. Reproducibility (correlation) of two waveforms expressed as a percentage: automatic calculation. Total OAE response is root-mean-square amplitude of signal waveform. Total noise is root-mean-square amplitude of noise waveform.
Analyzed in narrow-band frequencies (e.g., half-octaves) FFT. Signal amplitude, noise floor amplitude, and SNR reported. Frequency x-axis and SNR on y-axis. Other parameters typically displayed:
Stimulus intensity, Stimulus stability (at least 70% is acceptable), Number of sweeps accepted vs. rejected
TEOAE present and normal
SNR > 6 dB in majority of frequency bands and
Overall reproducibility >70% and
Overall amplitude within normal limits for age
TEOAE present but abnormal
Responses present at <75% of frequency bands or
Overall reproducibility <50% even if responses present or
Overall amplitude below normal limits for age
Less than two frequency bands with SNR >6 dB and
Overall reproducibility <50%
Stimulus parameters chosen to maximize separation between ears with normal hearing and hearing loss.
f2/f1 = 1.22
L1 = 65 dB SPL
L2 = 55 dB SPL
Stimuli should be ±3 dB of target (AAA, 2020)
DPOAE presence/absence: Present: SNR of at least 6 dB. Normal: Amplitude is WNL for age. Abnormal: Amplitude is <WNL for age
DPOAEs tell us primarily about the outer hair cell health near the f2 place because this is the primary site of generation. This is why the DP-gram plots DPOAE amplitude as a function of f2 frequency, not 2f1-f2 frequency.
DP-gram adult norms
DPOAE present and normal
SNR > 6 dB in majority of frequencies and
Amplitude within normal limits for age
DPOAE present but abnormal
Responses present at <75% of frequencies or
Overall amplitude below normal limits for age
Less than two frequencies with SNR >6 dB
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