Unit 2B (study cards) Flashcards
Otoacoustic Emissions/ OAE (these are spontaneous)
Sounds given off by your inner ear/cochlea when responding to sound stimulus.
Otoacoustic emissions (OAEs) are very faint sounds produced by the inner ear, specifically the outer hair cells within the cochlea, when stimulated by a sound, essentially acting as a tiny echo that can be measured by a microphone placed in the ear canal; they are used as a non-invasive way to assess the health and function of the inner ear, particularly in newborn hearing screening and diagnosing certain types of hearing loss.
result of movement of cochlear fluid
Outer Hair Cells generate OAE
Evoked OAE
we are causing them to happen. we are doing something to evoke a response and measure that.
TEOAE - transient Evoked: Play a sound into the ear (click or tone burst)–> wait about 5-10 msec –> cochlea plays same sound back to us (very soft sound)
DPOAE- Distortion product: we can measure the distortion introduced to the cochlea by measuring DPOAE. we can get specific frequency information (they factor in the movement of the OHCs to measure where the distortion happens in the cochlea)
Tuning Curves
how much sound is necessary to get a particular response from the basilar membrane, a hair cell, or a neuron, graphed as a function of frequency.
3 types:
1. basilar membrane tuning curve
-for each frequency, how much sound is needed to get a certain amt. of movement of the basilar membrane.
2. hair cell tuning curve
-for a given hair cell, we need somewhere btwn. 10 and 20 kHz activity for best characteristic frequency.
3. neural tuning curve
-we are measuring how much and quickly a neuron fires in response to a certain stimulus.
upward spread of masking
a lower frequency sound will cover up higher frequency sounds. but a high frequency sound can’t spread downward to mask lower frequency information.
The temporal theory of hearing
How does the volley theory help address a major limitation of temporal theory?
Cells will fire at the same pattern as an incoming sound (how fast a nerve is firing). With Temporal Theory, we are ignoring tonotopic organization.
A single neuron can’t respond to all of the sounds that we hear so we have the Volley theory…. A single neuron can correspond to a firing rate of 3,000 Hz. If we double this to 6,000 Hz we will need two neurons (passing volley back and forth to one another)
The place theory of hearing
what will happen if there is damage in a certain location on the basilar membrane?
We hear different frequencies when a neuron in a specific place along the basilar membrane is activated.
If there is damage at a certain place, you would have hearing loss at that place. This has to do with tonotopic organization.
TEOAE advantages
- The patient doesn’t have to do anything to participate in the TEOAE.
- They are fast so you can get a lot of information about a patient within a short window of time to determine whether the OHC’s are working.
- Used frequently in newborn nurseries.
DPOAE advantages
- breakdown of frequency specific information. We can vary intensity to measure cochlear function.
- Measures health of outer, middle and inner ear, but also allows us to add in frequency specific information and some ability to approximate a threshold.
- Could be used in a school.
Coding of Intensity
How do the place and temporal theories explain the coding of intensity?
The way the auditory system represents the loudness of a sound by translating its intensity (measured in decibels) into neural signals, primarily through the firing rate of auditory nerve fibers.
We can code for intensity by more spikes (temporal coding – firing rate of neurons) and broader pattern of activation (place coding-location on basilar membrane). Together, these determine how loud a sound is and what a sound is that is coming in.
Volley Theory
organized groups of fibers take turns firing on sequential peaks of the stimulus…..WE KNOW NOW THAT–>
on average, some neurons fire on every peak as long as the frequency is below about 4,000 Hz
Phase locking
a firing pattern of the inner hair cells in which the nerve firing is synchronized with the phase of the incoming auditory signal; thus, the nerve will only fire at certain phases of a periodic signal.
