lecture 8 - auditory perception

Question 1

what is sound?

Answer 1

Sound is caused by movement / vibration of an object.
The movement alternately squeezes air molecules together and pulls them apart.
Creates a longitudinal pressure wave in the air.

Question 2

how do we represent sound?

Answer 2

High points of pressure - molecules are squished up together

Question 3

what are properties of sound?

Answer 3

sound intensity level and perception of loudness

Question 4

what are physical properties?

Answer 4

amplitude, period

Question 5

what are derived properties?

Answer 5

intensity and frequency

Question 6

what are perceptual effects?

Answer 6

loudness and pitch

Question 7

how are properties of sound represented?

Answer 7

as a spectrum

Question 8

what is timbre?

Answer 8

Refers to that quality which can make two sounds with the same pitch and loudness seem dissimilar.

Sound quality, tone.

Related to complexity.

Question 9

what is in the outer ear?

Answer 9

has a perceptual effect
visible part of the ear - auricle and pinna
eardrum

Question 10

what is in the middle ear?

Answer 10

eardrum - ossicles - oval window

Question 11

what is in the ossicles?

Answer 11

Hammer, anvil and stirrup.

Question 12

why do we need the middle ear?

Answer 12

Funnelled down through the ear cannel - dont just get vibrations straight into the inner ear

Question 13

what is the inner ear?

Answer 13

cochlea
works as a frequency analyser and works as a transducer

Question 14

what does the inner ear do?

Answer 14

Breaks sounds down into components, converts mechanical energy into electrical activity

Question 15

what is the cochlea?

Answer 15

Stapes connected to the overall window - 2 fluid filled chambers separated by the cochlear partition filled with perilymphic fluid - sets up a series of vibrations - vibrations travel up and down, round and back

Question 16

what is the transduction process?

Answer 16

BM moves in response to vibrations in the perilymph.
BM vibrates at the same frequencies as the incoming sound!

These vibrations bend the stereocilia of the inner hair cells.
Allows positively-charged ions to enter the cell.
Triggers the release of neurotransmitters and an electrical signal is sent to the brain.

Question 17

what is place coding?

Answer 17

Different resonant frequencies at different points
Points of maximum BM displacement => frequencies of incoming sound.
Stimulates specific sets of inner hair cells.
Activates specific auditory nerve fibres.

Question 18

what is temporal coding?

Answer 18

BM moves in response to vibrations in the perilymph
Stereocilia stimulated by peaks in BM vibration.

Firing occurs at the period of the incoming waveform

Question 19

what is the difference between place vs timing?

Answer 19

place - where firing is coming from
temporal - when firing occurs

Question 20

when is place coding less reliable?

Answer 20

low frequencies

Question 21

what do inner hair cells do?

Answer 21

detects motion on the BM

Question 22

what do outer hair cells do?

Answer 22

amplifies motion of the BM

Question 23

what is intensity coding?

Answer 23

Relies on the fact that there are low- and high-threshold auditory nerve fibres.
Low-threshold fibres discriminate quiet and moderate (low- vs. medium-amplitude) sounds.
High-threshold fibres kick in to discriminate moderate and loud (high-amplitude) sounds.
The loudness of a sound ≈ total neural activity.

Question 24

what is the auditory pathway?

Answer 24

Cochlear nucleus, superior olive, inferior colliculus, medial geniculate and primary auditory area

Question 25

what does the cochlear nucleus do?

Answer 25

Sends neural activity to other nuclei in the brainstem

Question 26

what does the superior olive do?

Answer 26

analyses location

Question 27

what does the primary auditory area do?

Answer 27

analyses higher-order features

Question 28

why do we need to localise sound?

Answer 28

The location itself may be important. It may orient our attention to other things. Helps with source separation

Question 29

what is the location of the azimuthal plane?

Answer 29

sounds from the left - reaches the left ear first

Question 30

what is interaural timing difference?

Answer 30

a sound off to the side sounds diff to those that are in front of us

Question 31

what is interaural level difference?

Answer 31

When the sound is directly from the side Sound diffracts (bends) around objects smaller than its wavelength. Sound is blocked by objects larger than its wavelength.

Question 32

do low frequencies diffract around the head?

Answer 32

yes - high frequencies do not

Question 33

why does the pinnae have a funny shape?

Answer 33

amplifies some of the frequencies – changing the timbre of the sound slightly

Question 34

what is the neural coincidence model?

Answer 34

Sound coming directly infront of you – specific neuron fires and tells you where sound is coming from as it hits each ear at the same time

Question 35

what is the opponent process analysis?

Answer 35

system calculates the difference between the two sets to work out where a sound is coming from.

Question 36

how do we make speech sounds?

Answer 36

Larynx – voice box – force air from our lungs up through the holes creating sound Shape the spectrum of the sound – filter sound coming from our larynx, tongue, teeth, lips

Question 37

what are top down effects?

Answer 37

Speech perception relies on more than the acoustic signal! Top-down (cognitive) as well as bottom-up (perceptual) factors

Question 38

what is coarticulation?

Answer 38

The “same sound” is actually different depending on the acoustic context (neighbouring sounds)

Question 39

what is the McGurk effect?

Answer 39

Perceptual illusion: visually-presented sounds affect perception of the acoustic signal.

Question 40

what is linguistic knowledge?

Answer 40

Our perception of speech sounds is affected by the meaning of the context.