Lecture 9 Flashcards
what is sound
a wave that consists of areas of high pressure and low pressure, caused by the movement of air molecules caused buy the sound wave
high pressure
compression
low pressure
rarefaction
cycle time
time between compressions
perceptual phenomenon associated with frequency
pitch
perceptual phenomenon associated with amplitude
loudness (decibels)
perceptual phenomenon associated with complexity
timbre (quality of the sound)
what is hertz
number of waves per second
low wavelength=
low frequency, low pitch
typical human hearing range
20-20,000 Hz
short wavelength=
high frequency, higher pitch
infrasound
lower frequency
high frequency
ultrasound
high amplitude
loud
small amplitude
quiet
decibel scale
designed to correspond to human hearing
0 in decibel scale
threshold in human hearing
what is higher? Threshold of pain for hearing, or threshold of damage for hearing?
threshold of pain
complex wave components
fundamental frequency and harmonics
fundamental frequency
the wavelength of the longest component
what doe the fundamental frequency determine?
the pitch of teh sound
what do the harmonics determine?
the timbre and sound quality
purpose of the outer ear
to channel sound into our auditory canal
can amplify the sound a bit
protects auditory canal from particles etc in the environment
what is the eardrum
a membrane that vibrates when hit by sound drums
transduction of sound wave to … on the eardrum
mechanical energy
vestibular system
made of three semicircular canals
for balance
what liquid fills the vestibular canals
endolymph
how does vestibular system translate movement to the brain
when your head moves, endolymph moves in the vestibular canal
causes cupula to move
movement of cupula causes nerves to send a signal to the brain
Physical definition of sound
Pressure changed in the air or other medium
Perceptual definition of sound
The experience we have when we hear
What mediums can transmit sounds?
Elastic mediums
Pure tone
Occurs when changes in air pressure occur as a pattern described by sine wave
Sound frequency
The number of cycles per second that change the pressure in repeats
Use of decibels
To shrink large ranges of pressures
What is Po usually set as? Why?
20 micropascals
The pressure near hearing threshold for a 1000 Hz tone
First harmonic
Pure tone with frequency equal to the fundamental frequency
Higher harmonics
Pure tones with frequencies that are while number multiples of the fundamental frequency
Three tasks of the auditory system
1) Delivers sound stimulus to the receptors
2) Transduces the stimulus from pressure changes into electrical signals
3) Processes electrical signals so they can indicate qualities of the sound source
Pinnae
Structures that stick out from the sides of the head
Outer ear consists of
Auditory canal and pinnae
Auditory canal
Tubelike recess, about 3cm long in adults
What does the auditory canal do?
1) Along with wax’ protects the tympanic membrane at the end of the canal, and helps keep it and middle ear structures at a relatively constant temperature
2) enhance intensities of some sounds via resonance
Resonance
Sounds waves that are reflected back from the closed end of the auditory canal interact with the sound waves that are entering the canal
Resonant frequency
The frequency reinforced by resonance
Middle ear
Small cavity that separates the outer and inner ears, contains the ossicles and middle ear muscles
What are the ossicles
Malleus, incus and stapes
Transmission of vibration from outer ear to middle ear, in order
Tympanic membrane, malleus, incus, stapes
How does stapes transmit vibrations to the inner ear
Pushing on the membrane covering the oval window
Why are ossicles necessary?
Liquid in inner ear, air in outer ear. Air to liquid would result in poor transmission of vibration as the liquid is much denser
1) concentrated vibration of the large tympanic membrane onto the smaller stapes
2) being hinged to create a lever action, so that pushing down on the long end makes in possible to lift a heavy weight on the short end
Purpose of middle ear muscles
At very high sound levels they contract to dampen the ossicles vibration
1) reduces the transmission of low-frequency sounds
2) prevents intense low frequency components from interfering with our perception of high frequencies
May stop out own vocalisations and sounds from chewing interfering with our perception of speech
Main structure of inner ear
Fluid filled cochlea
Cochlear partition
Separated the scala tympani and the scala vestibuli in the cochlear
What does the cochlear partition contain
Organ of corti, which has hair cells
Two membranes extending the length of the cochlear
Basilar membrane and tectorial membrane
Stereocilia
Processes at the tips of hair cells that bend in response to pressure changes
How many towns of inner he air cells does the human ear contain
One
How many towns of outer hair cells does the human ear contain
3
What stereocilia are embedded in the tectorial membrane?
The tallest row of outer hair cells
Where do hair cells in the organ of corti detect vibrations from?
The basilar membrane
What are the main receptors responsible for generating signals that are sent to the cortex in auditory nerve fibres?
Inner hair cells
What results from the electrical signal in hair cells
Neurotransmitter release at the synapse separating inner hair cells and auditory nerve fibres, causing auditory nerve fibres to fire
Hair cells are activated when
Pressure increases
Hair cells are inactivated when
Pressure decreases
Tonotopic
Hair cells respond preferentially to a particular frequency
How far is tonotopic auditory organisation maintained?
As far as the primary auditory cortex in the temporal lobe
Neurones next to one another respond to neighbouring frequencies
What does the equal loudness curve demonstrate
Low frequency sounds need to be more intense to be perceived as equally loud
What is the head shadow effect
Sound to the further ear is attenuated because the sound must travel more distance and diffuse around the head
Location cues
Information created by the way sound interacts with the listeners head and ears
Two kinds of location cues
Binaural cues and spectral cues
Binaural cues
Depend on both ears
Spectral cues
Depend on one ear
Binaural cues determine the …. of sounds
Azimuth (left to right)
Two binaural cues
Interneural level difference and interneural time difference
Interaural level difference
Based in difference in the sound pressure level of the sound reaching each ear, caused by the acoustic shadow (head shadow)
Reduction of intensity of high frequency sounds to the far ear
Interaural time difference
Time difference between when a sound reaches the right and lest ear
What makes ITD larger
As the source is located more to the side
When will ITD be 0
When the source is located equidistant to each ear
What is b cue is most useful for determining location of high frequency sounds?
ILD
What is b cue is most useful for determining location of low frequency sounds?
ITD
Elevation
Up down
Azimuth
Left right
Cone of confusion
Elevation can be hard to determine as ITD and ILD can be the same at a number of different elevations
What helps us determine localisation in elevation
Spectral cues
How is elevation determined (spectral cue)
By difference in the distribution of frequencies that reach the ear from different locations.
Caused by: auditory stimulus is reflected from various folds of the pinnae before it enters the auditory canal
Auditory streaming
Stimuli grouped into streams by proximity in:
Space
Time
Frequency
