Lecture 27: The Auditory System Part 2 Central Auditory System

Question 1

What are the six major synaptic steps of the auditory system?

Answer 1

1. Hair cell
2. Cochlear nuclei
3. Superior Olivery Nuclei
4. The inferior colliculus
5. Medial Geniculate Body
6. Auditory Cortex

Question 2

Binaural input

Answer 2

you get input from both of your ears on the nuclei that is outside of cortex

Question 3

What are the two types of cues that compute where a sound is coming from?

Answer 3

i. Interaural level differences (ILD)

ii. Interaural time differences (ITD)

Question 4

What are interaural time differences (ITD)?

Answer 4

The difference in the time of arrival of a sound at the two ears
-since sound travels at a finite speed, a sound from the side will reach one ear before it reaches the other ear

Question 5

What is the trapezoid body?

Answer 5

Crossing auditory fibers at the level of the pons

Question 6

Where is the computation of ITD taking place?

Answer 6

At the medial superior olivery (MSO) complex
Inner ear hair cells synapse at cochlear nucleus and the project to the MSO
-two excitatory inputs arrive at MSO
-what’s remarkable is that they are activated SIMULTANEOUSLY at the nucleus contralateral to the direction of your sound…
-the thinking is that the shorter the distance it is between where sound is coming and one ear, the more distance it needs to travel in the head to make up for the speed with which the sound travels in the other ear

Question 7

How is superior olive organized?

Answer 7

i. medial superior olive

ii. lateral superior olive

Question 8

What is the Interaural level difference?

Answer 8

It detects the loudness of a sound (as in inferior, superior, etc.)

Question 9

Where is interaural level difference computed?

Answer 9

Lateral superior olive (the two L’s go together)

Loudness = lateral

Question 10

Rarefaction

Answer 10

reduction of an item’s density

Question 11

How do you know if something is anterior or posterior and also inferior/superior?

Answer 11

You use monoaural cues
-you learn to learn HOW sound travels into your ear
As shown in picture below, each path represents a different point in space at which sound is being transmitted

Question 12

How often do you have to learn or relearn 3-D spatial relationships?

Answer 12

All the time!
Example: baby to adult means your head grows…this changes the way sound is interpreted and you have to relearn the stimuli
-however relearning only takes a couple of days

Question 13

What are the three main levels of processing in auditory cortex?

Answer 13

i. core
ii. belt
iii. parabelt

Question 14

Where is the primary auditory cortex located?

Answer 14

Heschl’s gyrus

Question 15

How is the frequency processing of the auditory cortex organized?

Answer 15

Tonotopically

Question 16

Wernicke’s aphasia

Answer 16

you don’t undertand speech

Question 17

Broca’s aphasia

Answer 17

you can’t produce speech

Question 18

Arcuate fasciculus

Answer 18

connects wernicke’s and broca’s

-lesion means you can’t repeat stuff

Question 19

How are the different parts of the auditory cortex tuned?

Answer 19

They have selectivity for certain types of sounds that increases between primary and non-primary auditory cortices

- as you go from core outward, neurons get tuned for processing more cmplex information
- also becomes more specific to a stimuli as you go outwards….vs. something at the core that will respond to anything

Question 20

What is the functional differentiation among core, belt and parabelt?

Answer 20

Core is tonotopic and responds to simple sounds

Belt and parabelt are not tonotopically organized and respond to more complex sound

Question 21

As you go from primary to secondary auditory areas…

Answer 21

Neurons become more specialized for certain types of stimuli

Example: Wernicke’s area = activated by words more than primary auditory cortex

Question 22

What auditory problem is cortex solving?

Answer 22

Brain is able to break up all the acoustic stimuli and break it up/appreciate to distinct parts
When you hear a band play, you hear all the individual sounds (like you can tell the guitar is different from the singer’s voice)

Question 23

What is the clinical relevance of how cortex distinguishes sounds?

Answer 23

This capacity is significantly impaired in older folks and those with hearing loss

- folks with cochlear implants are particularly impaired
- cognitive dementia is precipitated by loss of sensory function

Question 24

How is the problem of sound differentiation solved?

Answer 24

Solution: detect regularities in an auditory stimulus and “link” these regularities together to form a PERCEPTUAL REPRESENTATION
-these representations are called AUDITORY OBJECTS
Example: internal representation of sound…for instance, I associate the USC fight song with a positive representation, so no matter what intensity and pitch, I can recognize the USC song

Question 25

Auditory objects

Answer 25

Representations of sound that is NOT dependent on stimulus

-by making perceptual, internal representations, you can recognize a song independent of tempor, pitch, timbre, etc.

Question 26

How do you group and delineate between sounds?

Answer 26

i. Similarity: elements that are similar in physical attributes tend to be grouped
ii. proximity: elements that are close together in space or time to be grouped
-elements in close frequency are grouped
-elements in close timbre are grouped
iii. Continuity: elements that appear to follow in the same direction to be grouped
Example: when you have gaps in a sound, your mind fills in the gaps and you continue to the hear the background rhythm
iv. Common fate: elements that appear to move together tend to be grouped

Question 27

What are abstract categories?

Answer 27

-categories based on higher-order or semantic information. Not based wholly on perceptual similarity

Question 28

What is the purpose of the inferior colliculus?

Answer 28

Inferior colliculus combines the complex tuning curves from the Dorsal Cochlear Nucleus with the sound localization info at the Superior olivery cochlea

Question 29

Where is abstract and perceptive representation of sound encoded?

Answer 29

In the auditory cortex