Auditory System II

Question 1

There are two different kinds of information the brain can use to compute a map of auditory space.

What are the two cues?

Answer 1

Interaural intensity differences (IID)

and

Interaural timing differences (ITD)

Question 2

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.

Answer 2

left

right

right

Question 3

The differences in the loudness of a sound reaching our two ears is called ______________________.

Answer 3

Interaural intensity difference (IID).

Question 4

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.

Answer 4

left

right

Question 5

The differences in the time at which a sound reaches the two ears is the ____________________.

Answer 5

Interaural timing differences (ITD)

Question 6

What is the interaural timing difference for a sound directly in front of us?

Answer 6

0 –> sound will reach both ears at the same time

Question 7

What is the interaural intensity difference for a sound directly in back of us?

Answer 7

0. The shape of the external ear actually helps distinguishing front from back.

Question 8

What are good samples that are particularly good at localizing sounds?

Answer 8

Barn owls –> which hunt at night

Question 9

Why are owls particularly good at localizing sounds?

Answer 9

They have specialized external ears that help them to localize the elevation( vertical location) of a sound using interaural intensity differences (IID).

Question 10

Looking at the owl anatomy

Where is the right ear located?

Where are the dense feather located?

Answer 10

The right ear is higher than its left ear

The dense growth of feathers above the left ear

Question 11

Sound coming from (above/below) the owl will be attenuated in the left ear

(attenuated; having reduce in force)

Answer 11

above

Question 12

For a sound coming from (above/below) the owl the sound attenuated in the right ear

Answer 12

below

Question 13

IID (interaural intensity differences)

Cells in the owl’s _______________ encode interaural intensity differences.

Answer 13

Nucleus angularis

brain stem area

Question 14

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.

Answer 14

True

Question 15

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.

Answer 15

False

The sparse feathers are above the left ear

Question 16

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

Answer 16

positive

negative

Question 17

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.

Answer 17

True

Question 18

________________ 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.

Answer 18

Nucleus angular

left

right

Question 19

Different individuals cells in the complex have _____________ from the left ear (excitation) connection than they do from the right ear (inhibitory) connections

Answer 19

Different synaptic weights

Question 20

These different synaptic weights may be due to

(I) ______________________________

(II) ____________________________

Answer 20

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

Question 21

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

Answer 21

Cell # 1 will not reach the threshold and will not fire

Question 22

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?

Answer 22

Cell #1 at this point receives twice as much excitation as inhibition and Cell #1 gives a good response

Question 23

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

Answer 23

It will fire twice as many spikes per second as it did at point B

Question 24

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

Answer 24

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

Question 25

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?

Answer 25

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.

Question 26

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?

Answer 26

Excitation and inhibition for Cell #2 are equal so the cell does not reach threshold and does not fire

Question 27

What is the population code?

A firing of a ______ number of different cells in order to determine the _________ of a sound in space.

Answer 27

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.

Question 28

Interaural timing differences are encoded in owl _____________.

Answer 28

Nucleus laminaris

Question 29

Interaural timing difference (ITD) tell the owl the ___________ location of a sound.

Answer 29

Azimuth (left/right)

Question 30

The ITD circuit depends on having _____ built into the circuit.

These ______ are due to ___________.

Answer 30

delays

delays

thin, unmyelinated axons.

Question 31

Solve the following two examples

Answer 31

Question 32

True or False: Information from the owl’s IID and ITD system come together in the owl’s auditory tectum

Answer 32

True

Question 33

In the owls auditory tectum there is a ________________.

Answer 33