Week 3 Flashcards
types of OAEs (32 cards)
list the three physiological processes important for OAEs
1) the passive mechanics of the cochlea
2) the cochlear potentials
3) the active process of the cochlea= electromotility (main player of OAEs)
the passive mechanics of the cochlea explanation
there is a passive traveling wave which is frequency dependent
*does not travel along the basilar membrane but is caused by a pressure difference between cochlear partition, note that is there is a discontinuity of the BM, there is still a traveling wave beyond that point because of this
the cochlear potentials explained
basically the cochlea has a battery inside to create a current to send signals to the nerve
*endolymph and hair cells have a voltage difference of 150mv, this creates the voltage and current that goes through the hair cells
the active process of the cochlea explained
- 2 mechanisms compliment each other
- –1= stereocilia MET channels which are controlled by K+ and CA+2 current
- –2= electromotility (prestin)
what are the two proposed hypotheses for how OAEs arrive to the ear canal
1) backward traveling wave= pressure change that propagates in reverse
2) acoustical compression wave=fluid compression wave
when do OAEs arrive to the ear canal
instantaneously after presentation of signal
what does research say is the correct hypothesis as to how OAEs get to the ear canal (as of now)
*compressional wave instead of backwards traveling wave
what are the 2 different ways to classify OAEs
- stimulus based (more popular)
* mechanism based (newer)
break down of OAEs using the stimulus based classification
- spontaneous
- –no stimulus
- –synchronizing stimulus (present signal, but then wait a bit before doing measurement)
- Evoked
- –TEOAE
- –DPOAE
- –SFOAE
spontaneous OAEs
(SOAEs)
- no stimulus, just probe in ear and sit quiet and see what happens
- prevalence increased from 40% -80% over time (equipment improvement)
- infants have larger/stronger than adults
- females have larger/stronger compared to males
- –there is a hormonal component
- amplitude is usually -15 to 0dB SPL, 800-4000Hz
- presence is not related to hearing sensitivity, the number of SOAEs is a better indication and if people have them they normally have sharper tuning curves
- ototoxicity and noise exposure could make them disappear
- large SOAEs could result after cochlear damage
stimulus frequency OAEs (SFOAEs)
- stimulus is pure tone and measure response associated with that pure tone
- challenges are differentiating between the response and the stimulus itself
what are the two ways to measure SFOAEs
1) suppression
* you record at a moderate level (20dB SPL) and then at record with a suppressor at a high level neighboring frequency (60dB SPL), then subtract the two to get the OAE without the stimulus itself (vector subtraction)
2) compression
* you present at a low level (20dB SPL) and a high level (60 dB SPL). then scale down the 60 dB response by 100 times and subtract the 20 dB signal to remove the stimulus
Transient Evoked OAEs (TEOAEs)
- stimulus is click at 80 microseconds
* looking at amplitude of response vs noise level at frequency bands
distortion product OAEs
- use 2 frequency stimuli with specific relationship between frequencies
- when you present 2 frequencies together, you get distortions
- –the most common is the cubic difference tone which is 2F1-F2
what are the 3 mechanism based classifications of OAEs
1) reflection emissions
2) distortion emissions
3) mixed emissions
- –these are based on the reverse propagation theory
reflection emissions (place fixed)
- are random reflections happening within the cochlea
- there are irregular distributions of OHCs which don’t change place which is why they are place fixed
- so traveling wave propagates and different OAEs are emitted at irregularities and reflected back to the ear canal
- SOAEs are pure reflection (background and internal noise cause activation of BM which is random physiologic noise)
distortion emissions (stimulus fixed)
- distortions of the stimuli
- also known as wave fixed
- example is DPOAE, specifically basal product DPOAE
mixed emissions
- both reflection and distortion together
- TEOAEs are mainly reflection but with distortion especially at lower levels
- apical DPOAEs have a reflection component suppressed (using masking noise)
- SFOAEs
standards for OAE equipment
- important to control for basic requirements
- no ANSI standards
- IEC (international electromechanic commission) 60645-6 (2009) guidelines for screening and diagnostic equipment
- all equipment must be FDA approved
hardware for OAEs
- computer for generation, recording, analysis and display
- 2 probes (many just one) for delivering stimulus
- analog to digital converter allows computer to process signals
- digital to analog converter allow computer to generate sound to ear (on per speaker/probe)
- speaker drivers and mic preamplifier
nyquist theorem
the sampling rate must be at least 2F the highest analog frequency component (all analog to digital converters should follow this)
aliasing
when there are not enough samples of a signal to truly represent what is occurring
system distortion of OAEs
happens at high levels
*use a 2cc coupler to measure OAE response at all levels
cross talk with OAE equipment
- can affect stimulus levels (and all stimulus levels)
- manufacturer should report it on the spec sheet (20dB or lower)
- ER-7 mic used in OAE probes: 40 dB below 5kHz and 20dB b/t 5-10 kHz
- current clinical systems are safe up to 8 kHz
