Final Lecture 15: March 19 Flashcards
(32 cards)
what is Tonotopic organization:
An arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency.
where is the where pathway
parietal lobe
where is the what pathway
temporal lobe
Hearing loss can be caused how
- Loss of sound conduction to the cochlea (conductive hearing impairments).
ex. : cerumen buildup in the auditory canal, otitis media, etc. - Damage to the cochlea (sensorineural hearing impairments).
ex. : congenital, drugs, age, chronic or phasic exposure to loud noises, etc.
what is Tinnitus
is the perception of sound in the absence of sound waves.
who has Tinnitus
Prevalence increases with age. When severe, tinnitus can cause insomnia
Tinnitus is often associated with what
hearing loss.
there is no treatment
give a hypothesis as to why tinnitus happens
One leading hypothesis is that following hearing loss, the brainstem increases the «gain» in auditory pathways to compensate, which also amplifies «neural noise», thereby causing tinnitus.
what is Azimuth:
The angle of a sound source relative to the centre of the head.
what is Interaural time differences:
The difference in time between a sound arriving at one ear versus the other
Listeners can detect interaural delays of as little as what
10 μs (0.01 ms).
what is the Physiology of ITD:
Coincidence detector neurons in the superior olive are tuned to detect different ITDs
A coincidence detector neuron detects an action potential that took 850 μs to travel from the left cochlear nucleus and 600 μs to travel from the right cochlear nucleus.
We could say that this particular coincidence detector neuron is tuned to an ITD of: 1450 μs 600 μs 250 μs 850 μs
250 μs
A coincidence detector neuron detects an action potential that took 850 μs to travel from the left cochlear nucleus and 600 μs to travel from the right cochlear nucleus.
And the sound was coming from…
The left
The right
And the sound was coming from…
The left
A coincidence detector neuron detects an action potential that took 850 μs to travel from the left cochlear nucleus and 600 μs to travel from the right cochlear nucleus.
Therefore the neuron is located in…
The right superior olive
The left superior olive
The right superior olive
ILD is largest wherw
at 90 degrees and –90 degrees
ILD is non existent where
for 0 degrees and 180 degrees.
ILD decreases with frequency becausewhy
the long wavelengths of low-frequency sounds easily “bend around” the head.
In general, long or short wavelengths are always more resistant to obstacles (sound, light, etc…).
In general, long wavelengths are always more resistant to obstacles (sound, light, etc…).
what is the Problem: ITDs and ILDs
can’t tell us how far away an object is on a given azimuth
Ex.: for an azimuth of -60 degrees, ITD will always be -480 μs even if in absolute it takes more time for a sound to travel from a farther distance.
10 meters: left ear = 400 μs, right ear = 880 μs
100 meters: left ear = 4400 μs, right ear = 4880 μs
what is Inverse square law:
the intensity of sound decreases as a function of the inverse (i.e. «one divided by») of the square of the distance
- > sound decreases with distance
- > it’s harder to tell small differences in distance between two objects if they are far away than if they are close.
give the equation for Inverse square law:
Intensitydistance «t» = Intensitysource/distance2
Problem: How can I tell if a source is loud and far away vs close but quiet
Solution: The spectral composition of sounds changes with distance
- > In general, long wavelengths are always more resistant to obstacles (sound, light, etc…).
- > sources that are far away are likely to have encountered more obstacles.
- > air also has «sound-absorbing» qualities
- > therefore the intensity of higher frequencies decreases as a function of distance (note that this only starts to have a real impact for distances > 1000 meters)
Solution: Distal sounds have more reverbarated than direct energy.
Problem:
ITD for a sound coming from these two azimuths is exactly the same.
ILD for the same azimuths should also be very similar.
-> there will be small difference because the head is not perfectly round but it will be negilgeable.
-> If you consider all three dimensions this makes a «cone»
give the solution
Solution # 1: Moving your headwill change the «cones of confusion». The only point that will retain its ITD and ILD is the «real» source
Solution # 2: The pinna (and also ear canal, head and torso) slightly distorts the amplitude of certain frequencies as a function of elevation.
Ex.: sounds coming from an elevation level of -50 degrees loose a lot of intensity (dB) between 8000 and 11000 Hz.
