Auditory perception Flashcards
define a sound
the change in pressure in the air through bands of condensation and rarefaction
define condensation
high pressure band of air
define rarefaction
low pressure band of air
define frequency
number of cycles, measured in Hz
define amplitude
the increase or decrease in pressure tha forms a cycle of sound
what the normal sound range for humans
20 - 20,000 Hz
how does frequency influence pitch perception
higher frequency = higher perception of pitch
how do we percieve loudness
high amplitude = loud
low amplitude - quiet
what are tones
harmony of different frequencies
contains a fundamental frequency which is the first harmonic and most closely reated to the tone we percieve, and higher harmonics which are multiples of the fundamental frequency
define the periodicy of pitch
sound periodicity refers to similarities in wavelength - spacing between harmonics governs repetition rate
can have same tone without fundamental freq - not all harmonics necessary to get same repetition rate
Describe loudness
‘sound intensity’ - size of amp/wavelength
Describe pitch
high pitch = high freq - governed by frequency of cycles
Describe tone chroma
Value of notes within an octave ie all c note have same chroma from diff octaves
A tone chroma is each fundamental frequency x 2
Describe timbre
Sounds have same tone (fundamental freq) but diff harmonics
Therefore diff for diff instruments
How does attack delay influence timbre
Determines perception of speed
Ie plucked guitar faster than breath controlled bassoon
What is the pinna
Outer ear
Focuses sounds waves into auditory canal
What are the ossicles
Act as amplifiers
Malleus, incus and stapes
Connect from tympanic membrane (end of auditory canal) to cochlear
What do the ossicles do
Concentrate vibrations from tympanic membrane
Increase air pressure x20 to vibrate chochlear
Sound propagate through auditory canal and intro air pressure diff to tymp causing movement
Malleus moves incus which moves stapes in fulcrum action - connect to oval window
How is sound perceived in the chochlear
sound down externaul auditory canal to tympanic membrane
-freq of vibration = pitch, intensity = loudness
ossicles concenrate vibration onto oval window
vibrations in cochlear fluid due to flexibility of round window - dissapates
vibrations up scala vestibuli to apex
vibrations down scala tympani to round window
organ of corti on basillar membrane on cochlear duct between vestibuli and tympani move in relation to vibrations - cillia on hair cells move, hair cells elongate/contract - send ap via auditory nerve and amp
How do the inner hair cells propagate an AP
Move in relation to pressure waves
Left and right motion opens ion channels producing bursts of electrical signals
up and down motion of basillar membrane elongates and contracts hair cells for amplification
Ap transfers to auditory nerve fibre
What determines rate of firing in inner hair cells
Sound frequency
Determines speed and movement
What is the basilar membrane
Where vibrations are converted to electrical impulses
Pressure diff due to move of ossicles at oval window between scala vestibulli and tympani
Cause basilar membrane to move up and down
Hair cells move in relation to basilar and send ap down auditory nerve
How does the cochlear act as an amplifier
Hair cells elongate when moved in one direct and contract in other
What is related to the representation of pitch
Primary auditory cortex
Diff freq mapped tonotopically
Lowest at anterior
Highest at posterior
What is temporal coding
Location irrelevant
Pitch coded by firing rate of nerve cells
Bender and wang 2005
Temp coding is determinant of pitch below 5000HZ
What is place coding
Pitch identified by anatomical location of action in basilar membrane
Bender and wang 2005
Determinant of pitch above 5000HZ
How is pitch related to frequency
High freq = high pitch
Temp coding and pitch
High freq = high pitch even below 5000 HZ
High firing rate = high freq
Phase locking
What is phase locking
auditory neurons have refractory period of max 5000hz (phase lock)
for higher pitches, neurons fire simultaneiously mimicing the higher frequency
Place coding and pitch
Low freq cause firing at apex
High freq cause firing at base
How is sound localised
It is not like vision
Do no review positional info as sound spread out over cochlear
Use binaural cues
How is sound localised
Elevation (above or below?)
Azimuth (left or right?)
Distance
Define inter aural time diff (ITD)
If sound directly in front then reach both ears at same time
At an angle, will reach one before the other
Determines azimuth - direction of sound by time taken to reach each ear
What is an acoustic shadow
When sound reach one ear first and is masked by head from reaching other ear
Less likely if freq Lower
Describe the cone of confusion
Elevation cannot be distinguished by ITD
time to reach the same at diff elevations
Must use monaural cues
What are monaural cues
Info about elevation
Determine by spectral cues and distribution of freq that reach the ear
Pinna filters sounds - introduces diff delays between signals at diff elevations
Pinna provides cue for sound elevation
Describe the auditory pathway
1 cochlear nucleas
- from auditory nerve
2 superior olivary cortex
- signals from both ears meet
3 inferior colliculus
- binaural processes of information
4 medial geniculate nucleus
5 primary auditory cortex
COOL SONIC MG
Cochlear nucleas
Super olivary
Inferior colliculus
Medial geniculate
- primary auditory cortex
Describe Jeffres neural coincidence model
Detection of azimuth at neural level
In super olivary cortex
- A -
>- B -
Define axonal conduction delay
Time taken for AP to travel from initiation site to neural soma
What is tuning
Lateral position of sound is determined by the position of max activation of coincidence detector neurons tuned to diff ITDs
Tuning of a neuron for an ITD is determined by the difference in axonal conduction all delay in each ear -‘delay line’
Do mammals fit the neural coincidence model
Owls do - each neuron tuned to different ITDs
Mammals don’t seem to follow -
In rats, have wider tuning curve
Location of sound indicated by ratio of response between firing
Neurons more broadly tuned to a range of ITDs
What are the pathways for sound into the prefrontal cortex
Posterior belt area - special tuning ‘where’
Anterior belt area - sound identification ‘what’ - rauschecker & tion 2000 - neurons in monkeys respond to vocalisations in jungles
Both project onto PFC
what are the suggested processing streams of auditory information and what are their seperate functions
lamber and Malhorta (2008)
Investigate auditory parallel processing streams
Reversible coding deactivation:
Deactivate posterior = localisation deficit
Deactivate anterior = pattern discrimination defecit
Roles very specific
Describe the precedence effect
Sound takes many diff routes
Perceive sound and localisation based on first wavelength that arrives at our ears
Separate sources via ITD, ILD (interaural level (intensity) difference), onset time, pitch &I timbre
Describe stream segregation
One melody played together sounds like two separate sources
High and low notes within melody separate when played fast
Due to diff in pitches in melody and time
When slowed the melody becomes more fluid
Define phonemes
Basic unit of speech - shortest segment
If changes, word changes
Ie c/a/t = K/æ/t
Define formants
specific band of pressure that determines the photenic quality of a vowel (aeiou)
What are formant transitions
rapid change in frequency from a constant (cdfghjklmnpqrstvwxyz) to a voewl (formant)
use as a cue for articulation
how does the perception of formants differ for different words (Moore (2012)
Sound spectrogram of dormant frequencies
‘Di’ ‘du’
First dormant the same but second formant have different frequencies - ‘di’ much higher
How can context affect acoustic signal
Phoneme strong effect on other segments close to them
Co articulation - overlap in articulation in neighbouring phonemes
What is voice onset time (VOT)
Delay between when sound behind and vocal cords begin to vibrate
Contribute to perceptual constancy
Allows to identify co articulation of formants
How do faces influence speech perception
Speech is multimodal- use visual cues to aid understanding
Describe Mcgurk and McDonald (1976)
"Mcgurk effect" Multi sensory illusion Dub video of speech with a different constant Visual info incongruent with auditory Rely more heavily on visual and mishear
how can lip movement influence brain activity (Calvert 1997)
Watch lips move improves speech
Fmri - visual cues activate auditory cortex
Activate for silent speech-like movements
Describe von kregstein et al 2005 FFA
Fmri find activity in fusiform face area when hear a familiar voice
Localised separately to visual info
Emphasise link of speaker recognition over content
Describe warren 1970 speech restoration effect
Context knowledge of language
Speech replaced by cough or tone - pps report hearing missing word
Silent - don’t hear
turvey and von gelder 1976
Reaction to phoneme target faster than nonsense word utterances
Ie sin bat leg / jum baf teg
Phonemic restoration effect
Samuwel 1990
Speech perception determined by acoustic signal and context expectations
Sounds actually missing from a speech signal can be restored by the brain and may appear to be heard.
Easier if words longer and similar
how can context influence (Miller and isard 1963)
Words more intelligible in context
Subjects given sentence arranges in 3 ways
Grammatical - “gadgets simplify work around the house”
Ungrammatical - “between gadgets highways passengers the steal”
Anomalous - “gadgets kill passengers from the eyes”
In silence or with background noise
Best - grammatical in silence (89%)
Worst - ungrammatical with noise (3%)
Describe overall speech perception
Seems to be a mix between top down and bottom up processing
Knowledge and meaning mix with acoustic signal to produce own perception
Speech perception/production and the brain
Broccas area
- frontal lobe
- primarily speech production
Wernickes area
- temporal lobe
- primarily speech perception
Aphasiacs with damage to one stream still hold other ability
Dual stream model of perception
Hickok and poepel 2007
Ventral - ‘what’ - comprehension
Dorsal - ‘where’ - map acoustic to movements producing the speech
Define speech segmentation
Perception of individual words in a convo
Meaning and prior knowledge be responsible for organising sounds to words
how does language aquisition develop
Lang acquisition is a combination of experience dependent & independent mechanism
As a young age - segmentation occurs based in statistical relationship of neighbouring speech sounds
Becomes more experienced based
