Auditory pathways

Question 1

The _______ ______ carries information out of the cochlea

Answer 1

Auditory nerve

Question 2

The auditory system is ______ compared to the visual system

Answer 2

Bilateral

Question 3

Cochlear Nucleus

Answer 3

The first brainstem region that receives auditory signals from the cochlea, where initial sound processing occurs.
- message is processed on the same side as the ear sending the message (bilateral)

Question 4

Superior Olive

Answer 4

A brainstem structure involved in sound localization by comparing timing and intensity differences between ears.

Question 5

Inferior Colliculus

Answer 5

• A midbrain structure that integrates auditory information from various brainstem nuclei and plays a role in reflexive responses to sound.
• E.g. immediately orientating towards loud sound

Question 6

Medial Geniculate Nucleus (MGN)

Answer 6

A relay station in the thalamus that processes and transmits auditory information to the primary auditory cortex.

Question 7

Primary Auditory Cortex

Answer 7

The region of the cerebral cortex responsible for processing and interpreting sound information, located in the temporal lobe.

Question 8

Tonotopy:

Answer 8

The spatial organization of sound frequency processing in the auditory system, where different frequencies are mapped to specific locations along the cochlea and auditory cortex. S
- Similar frequencies will be processed by adjacent locations in the auditory cortex pathway and cochlea.

Question 9

Secondary auditory areas surrounding the primary auditory cortex that processes more complex sounds like speech.

Answer 9

Belt and parabelt regions

Question 10

2 pathways when the input leaves the auditory cortices

Answer 10

1. What pathway
2. Where pathway

Question 11

“What” Pathway

Answer 11

The ventral stream of auditory processing that identifies and categorizes sounds, such as speech and music, linking auditory regions to the temporal lobe.

Question 12

“Where” Pathway

Answer 12

The dorsal stream of auditory processing that helps determine the location and movement of sounds, connecting auditory areas to the parietal lobe.

Question 13

Auditory and visual information interact within these pathways

Answer 13

“Where” Pathway and “What” Pathway

Question 14

Azimuth

Answer 14

Angle of a sound source relative to the centre of the head

Question 15

Interaural time differences (ITD)

Answer 15

The difference in time between a sound arriving at one ear versus the other
- The sound will arrive earlier to the ear that is toward the sound source than the contralateral ear

Question 16

Timing difference is related to the ______ of the object

Answer 16

Azimuth

Question 17

When is there no timing differences across the ears ?

Answer 17

With an azimuth of 0 (sound is directly in front) or 180 degrees (sound is directly in back)

Question 18

Largest ITD will be at ___ degrees

Answer 18

90 (sound coming from the side)

Question 19

The auditory system processes ITDs to …

Answer 19

Estimate location of sounds

Question 20

Listeners can detect interaural delays of as little as …

Answer 20

10 μs (0.01 ms)

Question 21

Physiology of ITD

Answer 21

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

Question 22

Coincidence detector neuron in the superior olives

Answer 22

• Will only fire an action potential if they receive a signal from the left and right cochlear nucleus AT the SAME TIME
• Are pretuned to certain ITD
  If a certain coincidence neuron is activated, the auditory system knows the ITD.

Question 23

Steps of ITD detection

Answer 23

Time 1 : 10 microseconds
- Nerve impulse arrives from the right towards the left and right superior olive
Time 2 : 350 microseconds later
- the sound reaches the left cochlea
- the nerve impulse from the left starts it race toward the right and left superior olive
Time 3 : 350 microseconds later
- 2 nerve impulses meet on a coincidence detector neuron in the left superior olive that is pretuned to perceive the 350 microseconds ITD

Question 24

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 ____
the sound was coming fro the right or the left ?
Therefore the neuron is located in…
The right or the left superior olive ?

Answer 24

250 μs
From the left
The right superior olive : had longer to travel to the contralateral side

Question 25

Interaural level difference (ILD)

Answer 25

Difference in level (intensity) between a sound arriving at one ear versus the other. - Sound in a certain location in space will be higher intensity (sound louder) on the side where they are coming from, because the head masks the sound for the contralateral ear

Question 26

Interaural level difference (ILD) is more pronounced for ____low/high frequencies

Answer 26

High

Question 27

Why is ILD more pronounced for high frequencies ?

Answer 27

High frequencies have shorter wavelengths that are more likely to be stopped by obstacles Longer wavelengths travel better in space : bend around the head, not blocked by it

Question 28

There is a higher interaural level difference for the ... angle

Answer 28

90° angle compared to 0 or 180.

Question 29

Brain structure that processes ILD

Answer 29

Superior olive compares the intensity level of the sound from left vs right ear

Question 30

Can ITD and ILD give absolute distance ?

Answer 30

No 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 31

Inverse square law of auditory distance perception

Answer 31

the intensity of sound decreases as a function of the inverse of the square of the distance. Intensity distance « t » = Intensity source/distance^2

Question 32

Like a bubble gum expanding and becoming thinner as it grows, sound will have a ______ amplitude as it expends

Answer 32

Smaller

Question 33

Because sound intensity decreases with distance, it’s harder to tell if small differences in distance between two objects if they are ...

Answer 33

far away than if they are close.

Question 34

How can we tell if a source is loud and far away vs close but quiet?

Answer 34

A sound with a lot of low frequencies in a spectrum is probably coming from a bigger distances : ->long wavelengths are more resistant to obstacles and travel further -> sources that are far away are likely to have encountered more obstacles. - Air also has « sound-absorbing » qualities : the intensity of higher frequencies decreases as a function of distance Note : only for distances > 1000 meters

Question 35

Degree of reverberation of a sound to tell sound distance

Answer 35

A distal sound from an object further away will have more reverberated energy (will have bounce around more, so will reach the ear from different angles)

Question 36

Problem at the root of the cones of confusion

Answer 36

ITD for a sound coming from a front and back 2 azimuths is exactly the same. ILD for the same azimuths should also be very similar.

Question 37

3 dimensions of confusions

Answer 37

1. 2 locations could have same ITD in 2D 2. The ITD cannot decipher the distance 3. elevation

Question 38

Cones need for every point on their surface, to have the same ____ : not informative of distance

Answer 38

ITD

Question 39

Many locations in space have the same ITD, and different ITDs will correspond to different _____

Answer 39

Cones

Question 40

Solution 1 to cones of confusion : moving the head

Answer 40

Moving your head will change the « cones of confusion ». - The angle of objects (Azimuths) change, and you compare the 2 cones of confusion, and find the common point : the real location of the sound

Question 41

Solution 2 to cones of confusion : the pinna

Answer 41

The pinna slightly distorts the amplitude of certain frequencies as a function of elevation : directional transfer function. - Helps because the cones of confusion are now 2D by removing elevation problem

Question 42

Directional transfer function

Answer 42

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 43

What does the pina change ?

Answer 43

Spectral composition of the sound (amplitude at each frequency) based on elevation

Question 44

How does the auditory system use pina sound distorsions to tell elevation ?

Answer 44

Auditory system learns this through experience and keeps updating it - It knows ahead of time that a sound with a specific spectral composition e.g. lacking certain frequencies will be coming from an elevated angle

Question 45

Auditory stream segregation

Answer 45

The perceptual organization of a complex acoustic signal coming from different directions into separate auditory events for which each stream is heard as a separate event.

Question 46

Using sound location for auditory stream segregation will be inneffective if...

Answer 46

The two sound sources are very close together The auditory system will then have to use grouping principles (like Gestalt)

Question 47

Grouping by frequency (pitch)

Answer 47

tones that have similar frequencies will tend to be grouped together. Distractors in the same pitch range = you cannot identify the melody

Question 48

Grouping by time

Answer 48

tones that are close together in time will tend to be grouped together. With repetition, 1) we lose the pause preceding/following the small “groups”, 2) there is accumulation of evidence that there are two separate streams

Question 49

Grouping by timber

Answer 49

tones that have similar timbre will tend to be grouped together

Question 50

Grouping by onset

Answer 50

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

Question 51

Continuity effect

Answer 51

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 52

Restoration effect

Answer 52

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.