Final Lecture 15: March 19

Question 1

what is Tonotopic organization:

Answer 1

An arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency.

Question 2

where is the where pathway

Answer 2

parietal lobe

Question 3

where is the what pathway

Answer 3

temporal lobe

Question 4

Hearing loss can be caused how

Answer 4

1. Loss of sound conduction to the cochlea (conductive hearing impairments).
   ex. : cerumen buildup in the auditory canal, otitis media, etc.
2. Damage to the cochlea (sensorineural hearing impairments).
   ex. : congenital, drugs, age, chronic or phasic exposure to loud noises, etc.

Question 5

what is Tinnitus

Answer 5

is the perception of sound in the absence of sound waves.

Question 6

who has Tinnitus

Answer 6

Prevalence increases with age. When severe, tinnitus can cause insomnia

Question 7

Tinnitus is often associated with what

Answer 7

hearing loss.

there is no treatment

Question 8

give a hypothesis as to why tinnitus happens

Answer 8

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.

Question 9

what is Azimuth:

Answer 9

The angle of a sound source relative to the centre of the head.

Question 10

what is Interaural time differences:

Answer 10

The difference in time between a sound arriving at one ear versus the other

Question 11

Listeners can detect interaural delays of as little as what

Answer 11

10 μs (0.01 ms).

Question 12

what is the Physiology of ITD:

Answer 12

Coincidence detector neurons in the superior olive are tuned to detect different ITDs

Question 13

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

Answer 13

250 μs

Question 14

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

Answer 14

And the sound was coming from…

The left

Question 15

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

Answer 15

The right superior olive

Question 16

ILD is largest wherw

Answer 16

at 90 degrees and –90 degrees

Question 17

ILD is non existent where

Answer 17

for 0 degrees and 180 degrees.

Question 18

ILD decreases with frequency becausewhy

Answer 18

the long wavelengths of low-frequency sounds easily “bend around” the head.

Question 19

In general, long or short wavelengths are always more resistant to obstacles (sound, light, etc…).

Answer 19

In general, long wavelengths are always more resistant to obstacles (sound, light, etc…).

Question 20

what is the Problem: ITDs and ILDs

Answer 20

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

Question 21

what is Inverse square law:

Answer 21

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.

Question 22

give the equation for Inverse square law:

Answer 22

Intensitydistance «t» = Intensitysource/distance2

Question 23

Problem: How can I tell if a source is loud and far away vs close but quiet

Answer 23

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.

Question 24

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

Answer 24

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.

Question 25

what is Directional transfer function (DTF):

Answer 25

A measure that describes how the pinna, ear canal, head, and torso change the intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation).

Question 26

what are the types of Auditory stream segregation

Answer 26

Grouping by frequency (pitch): 
Grouping by time:
Grouping by timber:
Grouping by onset
Continuity effect
Restoration effect

Question 27

what is Grouping by frequency (pitch):

Answer 27

tones that have similar frequencies will tend to be grouped together.

Question 28

what is Grouping by time:

Answer 28

tones that are close together in time will tend to be grouped together.

Question 29

what is Grouping by timber:

Answer 29

tones that have similar timbre will tend to be grouped together.

Question 30

what is Grouping by onset:

Answer 30

When sounds begin at different times they appear to be coming from different sound sources.

Question 31

what is Continuity effect:

Answer 31

In spite of interruptions, one can still “hear” a continuous sound if the gap is filled with noise. In that case the sound is perceived as continuing behind the noise. However, if the gaps aren’t filled with noise, the sound is perceived as separate “chunks”.

Question 32

what is Restoration effect:

Answer 32

In spite of interruptions, one can still “hear” a sentence if the gaps are filled with noise. In this case, higher-order semantic/syntaxic knowledge is used to “fill the blanks”. As for continuity effects, the effect vanishes if the gaps are not filled with noise.