intro to auditory neuroscience Flashcards
what is sound?
speed of sound in air
340 m/s
amplitude of sound
“sound level” or “sound intensity”
- expressed in log scale in dB sound pressure level (SPL)
frequency
- related to pitch
- expressed in hertz
- cycles per second
sound properties
- amplitude
- frequency
- phase
- timbre
phase
mostly ignored by human hearing
timbre
harmonic content
how can we change amplitude or frequency of sound?
- tuning forks (induce vibration)
- greater amplitude =
anatomy of the ear
- pinna
- auditory canal (skin and air)
- tympanic membrane (ear drum)
- auditory ossicles
- vestibular system
- auditory nerve
- cochlea
3 parts of the ear
- outer
- middle
- inner
ossicular chain
- malleus - rests on tympanic membrane (moves with vibration)
- incus
- stapes
(in middle ear, chain reaction of vibrations to move each other)
the ______ induces movement of the ______ _________ which is the communication from middle to inner ear.
stapes, oval window
the inner ear is filled with
fluid
why is fluid complicated for sound movement?
the amplitude decreases in fluid instead of air
how does the ossicular chain maintain amplitude when moving sound into fluid?
1:1.3 movement ration of amplification of the vibrations
- the stapes moves more than the malleus
tympanic membrane is larger than the oval window by a factor of ________ which increases sound wave pressure by ______
18.6x , 15x
the inner ear communicates with the
oral cavity
eustachian tube
the cochlea
- spiral structure
- made of bone
- membranes and fluids
parts of the cochlea
- base
- apex
- scala vestibuli
- scala tympani
how can the change of sound be produced in the cochlea?
- tympanic membrane vibrates
- vibrates malleus, incus, stapes,
- stapes vibrates the cochlear fluid and basilar membrane
place theory for frequency encoding in cochlea
different vibrations will cause vibrations in different locations of the basilar membrane
- high frequency is closer to base
- lower frequency is closer to apex
organ of corti
- innervated by auditory nerve fibers of CN VIII
mechanotransduction of the organ of corti
- relating of mechanical stimulus into action potentials
- have cilia (“hair cells”)
- support cells
what cranial nerve innervates the hair cells
VIII
stereocilia
- filled with actin filaments
- held together by tip links and ankle links
the links are primarily made of
proteins! which help open and close the channel that allows ion movement (K) entering the cilia
- initial part of mechanotransduction
mechanotransduction
theres a slide somewhere with a picture
endolymph vs perilymph
- endolymph = high in K channels low in Na channels
- perilymph = high in Na channels and low in K channels
each auditory nerve fiber responds to a
narrow range of frequencies
- this is because they innervate a specific region of the cochlea
how does the cochlea amplify incoming vibrations
- use of the hair cells
- stretch receptors (in cilia)
- bc sound amplitudes are tiny
function of outer hair cells
- they are the motors
- supply mechanical amplification
why is otoacoustic emissions (OAE) important?
- testing for hearing in babies
- test the movement of outer hair cells in response to sounds
auditory pathway
ascending auditory pathways in brain
- cochlea
- cochlear nucleus
- superior olivary nucleus
- inferior colliculus
- MGN
- auditory cortex
cortical tonotopy
cortical representation of sound intensities
don’t exactly know how sound is encoded????
experience dependent development of tonotopic maps
if you hear a sound frequency more often, you will develop a larger area of reception for the specific frequency of sound
what is the lowest sound detectable by the human ear?
0 dB
normal speech sound levels
60 dB SPL
damage to ear occurs at
140 dB SPL
the difference between the faintest (quietest) and loudest sound is
120dB SPL
what is the sensitivity of the human ear
differentiate 1dB
hearing loss and sounds in humans
human hearing frequency
range: 20 Hz to 20kHz
upper limit decreases with age
more sensitive to sounds between 1-4kHz
sound discrimination
- humans can discriminate 2 sounds that differ by 0.3% at 3kHz
- but require at least 3% difference at 100Hz
auditory brainstem response
- measuring responses right above the brainstem
- ## spinal ganglion
humans can discriminate 2 sounds that are located
as little as 3 degrees apart
- bc of 2 ears
go back to slide 700
head shadow
- the sound reaches the closest ear
- then the head gets in the way
- so sounds will not get to the ear further away which alters the way we hear the sound
- allows us to identify where the hearing is coming from
time difference
- the body can detect sounds in both ears
- but relies on the time difference between when the sounds are received
- allows us to recognize where the sound is coming from
duplex theory of sound localization
slide 702
when there is no difference detected between the two ears, the sound is
likely directly in front of us
sound localization in rooms
- usually sound goes on direct path from source
- reverberant energy
- we are not normally aware of reverberation but it influences subjective sound quality
- rooms = echo and reflect sound
3 time regions identified
- summing localization
- precedence effect
- echo threshold
summing localization
2 events fused, perceived location is a weighted sum of the 2
- less than 1 ms delay
precedence effect
only 1 sound perceived, direction of first sound dominant
- 1-5ms delay
echo threshold
2 sounds heard
- more the 5 ms delay
types of deafness
- conduction
- sensorineural
conduction deafness caused by
- punctured ear drum
- otisis media
- otosclerosis
sensorineural deafness caused by
- rubella
- professional deafness
- presbycusis
- destruction to inner hair cells
Rinne’s test
- bone conduction: put tuning fork on skull (don’t hear is conduction deafness)
vs - air conduction: vibration of tuning fork in air (don’t hear is sensorineural deafness)
