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sensation and perception 👁️ > auditory perception > Flashcards

auditory perception Flashcards

1
Q

cause of sound

A

vibration of an object
movement alternately squeezes air molecules together and pulls them apart
creates a longitudinal pressure wave in air

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2
Q

function of pressure against time

A

high points - portions where pressure is high
air molecules squished together

low point - low pressure
air molecules pulled apart

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3
Q

amplitude

A

distance between baseline and peak of wave

amplitude used to derive intensity
loudness

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4
Q

decibels

A

logarithmic scale of relative intensities
reduces wide range of amplitudes to smaller scale

calculated with reference to our hearing threshold
used to determine loudness

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5
Q

sound intensity level

A

way of representing amplitude relative to a reference perception of loudness

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6
Q

period

A

time taken to complete one wavelength

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7
Q

frequency

A

number of periods per second

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8
Q

pitch

A

attribute in terms of which sound can be ordered on a musical scale

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9
Q

timbre

A

refers to quality which can make two sounds with the same pitch and loudness seem dissimilar
related to complexity

pure and complex tones

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10
Q

pure and complex tones

A

pure = a single frequency

complex = made of more than one frequency
can be broken down into individual pure tones

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11
Q

how do sounds have a clear pitch?

A

partials must be integers multiples of the fundamental frequency
called harmonics
if a sound has inharmonic partials it will be unpatched

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12
Q

outer ear

A

visible part of the ear - auricle
not vital for perception but has an effect
shape of ear important to perception of sounds

ear canal
extends down to eardrum (tympanic membrane)
resonant frequency = 1-5kHz

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13
Q

middle ear

A

two membranes joined by bones:
eardrum - tympanic membrane

ossicles - 3 tiny bones
hammer, anvil and stirrup

oval window - membrane like eardrum

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14
Q

why are the bones needed?

A

vibrations must travel from air to fluid
creates an impedance mismatch

harder for vibrations to move through fluid than air
middle ear helps to deal with it
= impedance matching device

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15
Q

function of the 2 membranes

A

eardrum bigger than oval window
power of vibrations concentrated into oval window
lever action of hinged bones
action amplifies strength of vibrations

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16
Q

inner ear

A
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17
Q

cochlea structure

A

snail shaped
two chamber separated by the cochlear partition
filled with perilymphic fluid

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18
Q

cochlea function

A

work as a frequency analyser
breaks incoming complex sounds down into pure tone components

also works as a transducer
converts mechanical energy at these different frequencies into electrical activity to travel to the brain

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19
Q

cochlear partition

A

splits cochlea in 2

basilar membrane
runs with cochlea
on top of the membrane in organ of Corti

organ of Corti contains
tectorial membrane - hinges over top of basilar membrane
hair cells (inner and outer) - topped with steriocillia (smaller hairs)

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20
Q

how vibrations move around the cochlear

A

vibrations flow from oval window through first chamber through helicotrema (gap at end) down to round window (another membrane) an reflected back

vibrations move around through cochlear

base end - end nearest middle ear
apex - tip of curled up formation

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21
Q

transduction process

A

basilar membrane moves in response to vibration in the perilymph
membrane vibrates at the same frequencies as the incoming sound

these vibrations bend the stereocilia on the inner hair cells against tectorial membrane

allows positively charged ions to enter cell
triggers release of neurotransmitters and an electrical signal is sent up auditory nerve to the brain

22
Q

how is pitch detected?

A

place and temporal coding

23
Q

place coding

A

at the base, basilar membrane is anchored, narrow and stiff
at apex, it is free, wide and loose

means it has different resonant frequencies at different points along length

points of maximum BM displacement = frequencies of incoming sound
(displacement where BM is vibrating most)

stimulate specific sets of inner hair cells
activates specific auditory nerve fibres
the tonotopy (place coding) is represented all the way up to auditory cortex

24
Q

temporal coding

A

BM moves in response to vibration in the perilymph
BM vibrates at the same frequencies as incoming sound

stereo cilia stimulated by peaks in BM vibration
means firing occurs at the same period of the incoming waveform
- known as phase locking

stereocillia stimulated at peak as hairs are brushed against tectorial membrane
- at point of maximum displacement

means firings happen at peaks of BM motion
so firing correspond to period of incoming waveform
- allows brain to detect the pitch of sounds

25
Q

place coding at different frequencies

A

less reliable at low frequencies

areas of vibration on BM bigger at lower frequencies
less specific and precise encoding of pitch

26
Q

temporal coding at different frequencies

A

breaks down at high frequencies
not enough time for cells to recharge
leads to temporal smearing

peaks happening too close for coding to work
firings overlap and brain doest know which firings correspond to which peak of waveform

27
Q

function of inner hair cells

A

detect motion of basilar membrane

ion flow causes electrical signals to brain

28
Q

function of outer hair cells

A

amplify and sharpen motion of basilar membrane
= cochlear tuning

means we have good ability to discriminate different pitches

ion flow causes mechanical changes
expand and contract
motions amplify and sharpen basilar membrane action = more precise

29
Q

timbre coding

A

pitch represented by 2 mechanisms:

place coding = where on the BM firing comes from

temporal = when the firing is occurring

timbre represented by which combinations of fibres are active at the same time

30
Q

intensity coding

A

relies on the fact that there are low and high threshold auditory nerve fibres

low threshold fibres discriminate quiet and moderate sounds
- discriminate between low and medium amplitude sounds

high threshold fibres kick in to discriminate moderate and loud sounds
- discriminate between moderate and high amplitude sounds

loudness of sound = total neural activity
loud sound means all fibres are responding, quiet sounds mean only low responding

31
Q

auditory pathway

A

starts with cochlear

sent through auditory nerve to cochlear nucleus
- acts as a relay station
- send neural activity to other nuclei in brainstem

then travels through superior olive
- analyses location, where sounds are coming from
- relies on precise timing so happens early

then to inferior colliculus and medial geniculate
- analyse pitch
- relies on fairly precise timing, not quite as early as location processing

ends in primary auditory area
- analyses higher order features, such as timbre
- less reliant on precise timing

32
Q

auditory pathway simple

A

cochlear nucleus
superior olive
inferior colliculus
medial geniculate
primary auditory cortex

33
Q

azimuthal plane

A

whether sound is coming from the left or right

34
Q

intramural timing difference

A

sound from one side reaches that side first
eg left reaches left first

allows brain to detect direction sound is coming from
brain very sensitive to these small differences in time

35
Q

interaural level difference

A

if sound coming from left, right is shielded by the head

sound arrives at far ear later
arrives there quieter than other side

when sound directly from side, ILD depends on the frequency

36
Q

effect of frequency on ITD

A

to use ITDs, need to be able to match specific peaks in sound waves across both ears

at higher pitch = shorter wavelength
harder for brain to determine whether left or right came first
misinterprets where peaks are relative to each other

ITDs ambiguous or misleading at higher frequencies

37
Q

effect of frequency on ILD

A

sounds diffract and bends around object smaller than its wavelength
sound blocked by larger objects

low frequencies diffract around the head
- some sound reaches far ear
- got there later but at a similar frequency

high frequencies do not diffract
- creates a head shadow
- limited sound at the far ear
- creates a larger ILD

ILDs only useful at higher frequencies

38
Q

how is elevation of sound detected?

A

ITDs and ILDs don’t help
pinnae do

amplify some frequencies and reduce others
create spectral cues by changing incoming frequency spectrum
change the timbre

complex waveforms represented as different component frequencies
represented on a spectrum

when sounds come from different heights
shape of ears filter sounds in different ways
- creates different timbres depending on elevation of noise
= unique resonance patterns according to height

39
Q

sounds from the front vs back

A

sound from directly in front or behind = ITD of 0
- takes just as long for sound to get to ears from front as back
- equally as loud

pinnae create small level differences
we can also rotate our heads

40
Q

neural coincidence model

A

axons transmitting electrical signals representing sound from both ears
- acts as delay lines

axons connected to neurons
- act as neural coincidence detectors

means neurons only fire when stimulated at same time by information from left and right ear

measuring using ITD tuning curves
look at different neurons and measure firing rate across different ITDs
curve supports this model for some animals
- terrestrial more likely to use opponent process analysis

41
Q

how does the neural coincidence model work to determine angle of sound?

A

sound waves from straight ahead come in from both ears
travels along until both left and right ears reach and feed into same neuron at same time - then fires

this specific neuron during allows the brain to know that the sound in coming from directly in front

if sound comes from right, hits right ear first
signal comes in from right before left
left stimulated later than right
sounds reach neuron together causing it to fire
different specific neruon fired - allows brain to determine that it is from an angle

42
Q

opponent process analysis

A

involves 2 sets of broadly tuned neurons

neurons tuned to left half of auditory space - in right hemisphere
neurons tuned to right half of auditory space - in left hemisphere

system calculates the difference between the two sets to work out where a sound is coming from
- if most firing from left half, assume sound from left and vice versa
- smaller differences mean closer to centre
- no difference, assume sound straight infront

43
Q

how are speech sounds made?

A

vibrations from the larynx travel upwards through vocal tract

spectrum of sound is shaped by the articulators including:
- soft palate, hard palate, tongue, teeth and lips

and the resonant spaces (resonators) including:
- chest, throat, mouth and nasal cavities

larynx (voice box) contains folds of material
air forced from lungs through fold, making them vibrate
- vibrations create sounds

44
Q
A

speech perception relies on more than the acoustic signal
also reels on both top down (cognitive) and bottom up (perceptual) factor

45
Q

fricatives

A

sounds made by forcing air through narrow gap in articulators
eg s, sh, z

a lot of energy through lots of frequencies
but particularly in high frequencies
shown by dark bands

46
Q

vowel sounds

A

articulators can be used to shape our vocal tracts
creates vowel sounds
shown by stripy bands at lower frequencies
peaks in spectrum
- frequency components in vowel sounds that are particularly strong

47
Q

coarticulation

A

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

however we perceive these as being the same
known as perceptual constancy
reflects to down contribution of articulatory knowledge
know what is needed to make these sounds so can remove small perceptual difference

48
Q

McGurk effect

A

perceptual illusion

visually presented sounds affect perception of the acoustic signal
use of visual information inform interpretation of articulatory knowledge

49
Q

linguistic knowledge

A

our perception of speech sounds is affected by the meaning of the context

50
Q

phoneme restoration

A

if a familiar word is distorted (eg a missing sound) we put it back in without realising

influence of lexical knowledge

51
Q

Miller and Isard

A

perception of speech sounds is affected by the meaning od the context

normal sentences
grammatical string of words

played people these sentences and asked to repeat them back
- all sentences should have been equally intelligible

but intelligibility decreased as stimuli became less meaningful or grammatical correct

shows influence of semantic and syntactic knowledge
- regardless of quality of acoustic inputs
- contextual knowledge of linguistic factors essential for perception

52
Q

sine wave speech

A

formants replaced with pure tones
tracking the intensity modulations of those formants over time

sine wave speech can be learnt
has no fricative sounds etc only formants

but due to formants and coarticulations can be learnt
(formants influence perception of surrounding speech)
shows influence of phonological, lexical and syntactic and semantic knowledge

sensation and perception 👁️ (9 decks)

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