Auditory System II Flashcards
There are two different kinds of information the brain can use to compute a map of auditory space.
What are the two cues?
Interaural intensity differences (IID)
and
Interaural timing differences (ITD)
For example, if a tiger is to the left of us, the sound of the tiger’s roar will be louder in our _____ ear than in our ____ ear.
Because our head blocks the sound from reading our ____ ear.
left
right
right
The differences in the loudness of a sound reaching our two ears is called ______________________.
Interaural intensity difference (IID).
For example, if the tiger is to the left of us, the sound of the tiger’s roar will reach our _____ ear sooner than it will reach our ____ ear.
left
right
The differences in the time at which a sound reaches the two ears is the ____________________.
Interaural timing differences (ITD)
What is the interaural timing difference for a sound directly in front of us?
0 –> sound will reach both ears at the same time
What is the interaural intensity difference for a sound directly in back of us?
- The shape of the external ear actually helps distinguishing front from back.
What are good samples that are particularly good at localizing sounds?
Barn owls –> which hunt at night
Why are owls particularly good at localizing sounds?
They have specialized external ears that help them to localize the elevation( vertical location) of a sound using interaural intensity differences (IID).
Looking at the owl anatomy
Where is the right ear located?
Where are the dense feather located?
The right ear is higher than its left ear
The dense growth of feathers above the left ear
Sound coming from (above/below) the owl will be attenuated in the left ear
(attenuated; having reduce in force)
above
For a sound coming from (above/below) the owl the sound attenuated in the right ear
below
IID (interaural intensity differences)
Cells in the owl’s _______________ encode interaural intensity differences.
Nucleus angularis
brain stem area
True or False: Because the owl’s left ear had sparse feather blow it while the right ear had dense fathers below it, the sound below the owl is louder in the left ear.
True
True or False: Because the owl’s right ear has sparse feathers below it while the left ear has dense feather above it, the sound above the owl is louder in the right ear.
False
The sparse feathers are above the left ear
The responses of cells in the owl’s left nucleus angularis
IID is shown as the left ear intensity minus the right ear intensity
so the intensity difference is ______ for sounds which are louder in the left ear
and _________ for sounds which are louder in the right ear
positive
negative
True or False: Every individual cell in the left nucleus angular will tend to increase its response as the IID becomes more positive that is as the sound becomes relatively louder in the left ear than the right ear.
True
________________ recive exitctation from the ipsilateral ear and inhibition from the contralateral ear.
Therefore, in the left nucleus, angularis cells are excited by inputs from the ____ ear and inhibited by inputs _______ ear.
Nucleus angular
left
right
Different individuals cells in the complex have _____________ from the left ear (excitation) connection than they do from the right ear (inhibitory) connections
Different synaptic weights
These different synaptic weights may be due to
(I) ______________________________
(II) ____________________________
i. either to their receiving larger, stronger synapses from one ear’s
ii. to their receiving more synapses from one ear’s inputs than from the other
Cell #1 receives equal numbers of synapses from inputs from the two ears.
3 synapses from left ear inputs
3 synapses from right ear inputs
At Point A, IID is 0
The excitation and inhibition will cancel each other rout, so what is the response of Cell #1 at 0 IID?
Assume that it will recieve 10 spiker/sec at the excitation sysnapse
and 10 spikes/sec at inhibition sysnspe
Cell # 1 will not reach the threshold and will not fire
Cell #1 receives equal numbers of synapses from inputs from the two ears.
3 synapses from left ear inputs
3 synapses from right ear inputs
At point B –> the sound is relatively louder in the left ear than the right ear such that IID is 20dB.
What is the response of Cell #1 at 20 dB IID?
Cell #1 at this point receives twice as much excitation as inhibition and Cell #1 gives a good response
Cell #1 receives equal numbers of synapses from inputs from the two ears.
3 synapses from left ear inputs
3 synapses from right ear inputs
At points C, the IID is 40
What is the response of feel #1 at 40dB IID?
Let assume 20 spikes.sec from the left ear
and 5 spikes/sec from the right ear
It will fire twice as many spikes per second as it did at point B
Cell #2 receives fewer synapses from the right ear inputs than the left ear.
4 synapses from the left ear inputs
2 synapses from the right ear
At point A, IID is 0.
What is the response when Cell #2 is at 0?
assume that left ear get 10 spikes/sec
and 10 spikes/sec in the right ear
Cell #2 is therefore receiving twice as much excitation as inhibition at this point, so it will have a response equal to the response that Cell #1 has at point B
Cell #2 receives fewer synapses from the right ear inputs than the left ear.
4 synapses from the left ear inputs
2 synapses from the right ear
At point B IID is 20.
What is the cell response at 20 dB?
The cell is receiving four times as much excitation as inhibition, and the firing rate is twice as high as it was at point A.
Cell #2 receives fewer synapses from the right ear inputs than the left ear.
4 synapses from the left ear inputs
2 synapses from the right ear
What is the cell response when at -20 dB?
Excitation and inhibition for Cell #2 are equal so the cell does not reach threshold and does not fire
What is the population code?
A firing of a ______ number of different cells in order to determine the _________ of a sound in space.
Firing of a large number of different cells in order to determine the elevation of a sound in space.
For example, this figure cells with blue curves fire maximally for sound with 0.
Cells with black curves fire intermediate for 0.
Cells with green curves do not fire sound with 0 IID.
Interaural timing differences are encoded in owl _____________.
Nucleus laminaris
Interaural timing difference (ITD) tell the owl the ___________ location of a sound.
Azimuth (left/right)
The ITD circuit depends on having _____ built into the circuit.
These ______ are due to ___________.
delays
delays
thin, unmyelinated axons.
Solve the following two examples
True or False: Information from the owl’s IID and ITD system come together in the owl’s auditory tectum
True
In the owls auditory tectum there is a ________________.
