THE HEARING BRAIN

Question 1

Sound waves: What are they, physical and perceptual properties

(general)

Answer 1

The Auditory Stimulus: airborne sound waves

Traveling vibrations of air that alternate between compression (squeezing) and rarefaction (stretched apart) of air molecules

Sound waves have different physical qualities which are approximately related to how we perceive the sound

Question 2

frequency is :

measured in ___

Physical quality ____

perceptual quality ____

Answer 2

physical qualities which are approximately related to how we perceive the sound

Question 3

Amplitude

measured in ___

Physical quality ____

perceptual quality ____

Answer 3

physical qualities which are approximately related to how we perceive the sound

Question 4

overtones

measured in ___

Physical quality ____

perceptual quality ____

Answer 4

physical qualities which are approximately related to how we perceive the sound

Question 5

Answer 5

Question 6

Answer 6

Question 7

Answer 7

Question 8

basic pathway - sensation to perception

Answer 8

Receptors transduce the physical signal into a neural signal

• Before the receptors:
▫ Outer ear (pinna), auditory canal ▫ Middle ear (eardrum, ossicles)

• Outer and middle ears funnel signal into the inner ear

• Receptors are in the inner ear
▫ Hair cells located in the cochlea

Question 9

Sensation: stimulus affects a receptor

Answer 9

• Receptor transduces the stimulus: turns a

physical stimulus into a neural signal

Question 10

Perception:

Answer 10

interpretation of sensations to create a model of the world

Question 11

Outer ear

Answer 11

Pinna captures sound waves and funnels them inward

• amplifies certain frequencies: important for locating sounds

Question 12

Middle ear

Answer 12

Ossicles (malus incus and stapes)

tympanic membrane = ear drum

Question 13

Inner ear

Answer 13

COCHLEA —

Question 14

Auditory nerve

Question 15

Transduction in the cochlea

Answer 15

Pressure waves in fluid of cochlea cause basilar
membrane to move up and down
• Movement affects hair cells in the organ of Corti
▫ Movement causes the hair cells to fire action potentials
▫ Hair cells are thus the receptors for sound.

(Movement of the basilar membrane shifts the tectorial
membrane, which moves the sterocilia) = causes neurons to fire

Question 16

Stereocilia

Answer 16

Question 17

Hair cell transduction

Answer 17

Tip link • Movement of stereocillia
pulls on “tip links”
• Pulling of tip links open
ion channels; K+ enters
cell, depolarizing it and
causing neurotransmitter
release
• Stimulates neurons of
auditory nerve to fire action
potentials

Question 18

Sound amplitude and the basilar
membrane

Answer 18

Higher amplitude sounds make larger ripples in the
basilar membrane, causing greater opening of ion
channels

Question 19

Sound frequency and the basilar
membrane

Answer 19

• Basilar membrane is wedge shaped
▫ Goes from being narrow and stiff to wide and floppy

Sound frequency and the basilar
membrane
• Peak movement of the basilar membrane depends on
frequency
• Different frequencies vibrate different parts of the
membrane, activating different hair cells

Question 20

Auditory Pathway

Answer 20

Question 21

MGS

Answer 21

MEDIAL GENICULATE NUCLEUS

Question 22

Auditory cortex in temporal lobes

Answer 22

Question 23

Auditory nerve

Answer 23

Auditory Pathway
Axons from auditory neurons come together to form auditory nerve
Medial geniculate nucleus (of the
thalamus)

Primary auditory cortex in temporal lobes

Question 24

Primary auditory cortex (A1)

Answer 24

•AKA “Core” region
• Located in superior temporal lobe
•Receives input from thalamus
• Encodes simpler features of auditory stimulus
▫ E.g. neurons respond to a narrow range of
frequuencies
• Tonotopically organized

Question 25

Tonotopical organization

Answer 25

Question 26

Secondary auditory cortex

Answer 26

* of features, e.g. aBelt and parabelt regions * Respond to more complex features ▫e.g. broader range of frequencies; sums up information from A1 ▫May also respond to combinations certain loudness _and_ location •Notice this is like the hierarchy of processing we saw in the visual system. \*\* Notice this is like hierarchy in the visual system Kind of like how simple cells combine information from LGN center-surround cells

Question 27

“What” Versus “Where”

Answer 27

•Some evidence for two routes: ▫“What” route along the temporal lobes ▫e.g. anterior A2 responds to monkey calls (irrespective of location) •“Where” route projecting to the parietal lobes –e.g. posterior A2 responds to location of sound (irrespective of who is making it) \*\*\* Are there different parts of the brain that are specialized for processing what and where? What route: Different monkeys have different calls, like how we all have different voices Cells in anterior A2 will respond to particular identities (Monkey Phil) regardless of location (where Monkey Phil is) Like the what pathway in the visual system: respond to the same object regardless of where it’s located Where route: Responds to a call from a particular location, regardless of who is making the call (Monkey Phil or Monkey Steve)

Question 28

“Where” Processing: Locating Sounds Horizontal plane

Answer 28

•Horizontal plane: Inter-aural differences ▫Time differences –Sound takes longer to arrives at the ear that is furthest from the source – ▫Intensity differences –Sound waves decay with distance –Less intense in ear that is further from source

Question 29

horizontal plane

Answer 29

Horizontal plane: take advantage of having two ears If the sound reaches my left ear before my right ear, where must it be coming from? What if the sound reaches both ears at the same time? If the sound is louder in my right ear than in my left ear, where must it be coming from? Scent localization works on intensity differences

Question 30

“Where” Processing: Locating Sounds vertical plane

Answer 30

* Vertical plane: Distortions by pinnae * Increases some frequencies, decreases others depending on vertical location * Brain uses a learned model of how sounds get distorted (“head-related transfer function”) to infer sound location * What about animals that don’t have pinnae? \*\*\* Vertical: neither interaural delay nor intensity is going to differ as an object moves up and down Why do we have those wrinkles in our ears? Why aren’t they smooth? If you fill in the crinkles in the ears, people can’t tell where something is coming from vertically All of our ears are shaped differently, learn the shape of our own ears If you listen through someone else’s ears, can’t figure out the vertical location Owls: ears are at different heights on their heads, so can used horizontal localization techniques

Question 31

comparing hearing and vision

Answer 31

Question 32

Overall summary

Answer 32

•Hair cells in the cochlea transduce pressure waves into a neural code ▫Different frequencies stimulate different parts of the basilar membrane •Signal is passed through the MGN of the thalamus to auditory cortex in the temporal lobe ▫Separate pathways for processing “what” and “where” •Location can be determined by analyzing differences between the two ears (horizontal) and distortions by the pinnae (vertical)

Question 34

Outer ear

Answer 34

Pinna captures sound waves and funnels them inward • amplifies certain frequencies: important for locating sounds

Question 35

Ear drum aka \_\_\_\_\_

Answer 35

Tympanic membrane

Question 36

Middle ear Function? Process

Answer 36

Function: transmit sounds from outer ear to inner ear • Pressure changes make ear drum (“tympanic membrane”) vibrate Bones (ossicles) transmit the vibration to the inner ear. • Not a passive transmission, they amplify the signal (pressure changes) captured by the eardrum. • Push back and forth on the oval window

Question 37

Ossicles

Answer 37

Malus Incus Stapes “Bones”

Question 38

Inner ear

Answer 38

• Contains the cochlea • Cochlea is filled with fluid • Action of ossicles creates waves in the fluid

Question 39

........?.How do we hear? (Sensation)

Answer 39

Vibrations in air are Liquid Neurons