Section 5 Flashcards
How does sound come about?
From pressure fluctuations in the air
What determines the loudness of sound?
The amplitude of the sine waves that represent the air fluctuations
What is loudness?
The psychological aspect of sound related to perceived intensity or amplitude
How is amplitude measured?
Decibels
What does dB = 0 mean?
The pressure fluctuation corresponds to the minimal auditory sound for most people
TRUE/FALSE
dBs are more reflective of subjectively perceived sound than actual sound pressure
true
How does dB if sound pressure increases by x10?
Increases by +20
What is intensity of sound?
Corresponds to the energy of the sound wave when it hits a 2D surface, such as the eardrum
What is pitch?
The psychological aspect of sound related mainly to the fundamental frequency
What do we call sounds that only have one frequency?
Pure tones
Sounds that have a lower frequency have a _______ (lower/higher) pitch
lower
What is a spectrum of sound?
It’s an easy way of breaking down complex sounds using bars whose height represents the amplitude and the position on the X axis represents which frequency that sound is at
What is a harmonic spectrum?
The spectrum of a complex sound in which the energy is integer multiples of the fundamental frequency
What is a fundamental frequency?
The lowest-frequency component of a complex periodic sound
What does it mean if different spectra of complex sounds have the same fundamental frequency?
They will all have the same pitch
If several complex sounds have the same pitch, does that guarantee they will have the same loudness?
No, loudness will depend on the amplitude differences
What is timbre?
The psychological sensation by which a listener can determine that two sounds with the same loudness and pitch are dissimilar
If two sounds have different timbres, what does that tell us about their harmonic spectrum?
Their spectra are different
What is a missing-fundamental effect?
The fundamental frequency is missing in the harmonic spectrum, but the pitch listeners hear still corresponds to that fundamental frequency
How can we hear the fundamental frequency even if it is absent in the spectrum?
The superposition of the different harmonics will recreate a peak that has the frequency of the missing fundamental
Describe audibility of a sound
The combination of frequency and amplitude
What is an equal-loudness curve?
A graph plotting sound pressure level (dB) against the frequency for which a listener perceives constant loudness
List the three sections that make up the ear
Outer, middle, and inner
What structures make up the outer ear?
Auditory canal and pinna
What structure borders the outer and middle ear?
Tympanic membrane
What structure is at the border of the middle and inner ear?
Oval window
What are the three bones that transduce the sound signal to the oval window?
Malleus, incus and stapes
which ear structure amplifies sound signals?
The ossicles
There are two muscles part of the middle ear - what are they?
Tympani muscle and stapedius muscle
What is the role of the tympani and stapedius muscles?
Protect the ear from the sound being too loud by stopping the tympanic membrane and ossicles from vibrating
What two main structures make up the inner ear?
Vestibular organs and cochlea
What are the vestibular organs important for?
Sense of equilibrium
What is the cochlea important for?
Hearing
Inside the cochlea there is a fluid that is distributed across three main canals - list them
vestibular canal, middle canal, and tympanic canal
What two membranes separate the three canals?
Tectorial membrane and basilar membrane
Where is the organ of corti located? what does it do?
It is located on the basilar membrane and contains nerve cells that are responsible for hearing
What do we call the nerve cells located on the organ of corti?
Hair cells
How many hair cells are there?
4 in total - 1 inner and 3 outer
What do you call the tiny hairs on top of each hair cell?
Stereocilia
What part of the hair cells are attached to the tectorial membrane?
Stereocilia
What causes the basilar membrane to move up and down?
Movement of cochlear fluid
How does a change in air pressure transduce into an electrical signal?
The stereocilia on the hair cells have tip links that connect the stereocilia, and when they move back and forth it opens the link which allows K+ to enter the hair cell, causing the cell to depolarize and release neurotransmitter
What are the two main ways the auditory system can differentiate between different frequencies?
- Cochlear place code
2. Temporal encoding of frequency
Describe the structure of the basilar membrane
As the membrane extends from the base of the cochlea, it becomes wider and thinner, making the tip of the membrane more sensitive to lower frequencies and the base being more sensitive to higher frequencies
What is the cochlear place code?
The theory that because the sensitivity of the basilar membrane works via a gradient, specific frequencies will be related to movement of specific parts of the membrane
What is the role of characteristic frequency in the cochlear place code?
Auditory nerve fibers are selective for a given frequency, and these different fibers will be connected to different hair cells located at different points along the basilar membrane that corresponds to which frequency they are selective for
What are threshold tuning curves?
Describes the characteristic frequency for a specific auditory nerve neuron
Auditory nerve firing is phase-locked, meaning these neurons systematically fire at a given time point. When exactly will these neurons fire?
When the amplitude starts increasing because the liquid in the cochlea move upward which tilts the stereocilia and causes the hair cells to fire
What is the volley principle?
When the frequency is high the refractory period of the fibers does not allow the neurons to fire fast enough, but even if individual neurons cannot keep the pace, the whole population of neurons can still temporally encode the frequency
Which three nuclei in the brainstem will the auditory nerve from both ears project onto?
cochlear nucleus, superior olive, and inferior colliculus
The auditory nerve projects to the _______ (ipsilateral/contralateral) cochlear nucleus, but from the cochlear nucleus the information is sent to the ______ (ipsilateral/contralateral) and _______ (ipsilateral/contralateral) superior olive
contralateral, ipsilateral, contralateral
The inferior colliculus receives either ______ (direct/indirect) input from the cochlear nucleus or _______ (direct/indirect) input from the superior olive
direct, indirect
Once the information passes the inferior colliculus, what next brain structure does the information get sent to?
The medial geniculate nucleus in the thalamus
Where does the information travel after reaching the thalamus?
The auditory cortex
Where is the auditory cortex located? More specifically, where is the primary auditory cortex located?
Temporal lobe
lateral fissure
What structures surround the primary auditory cortex?
Belt and parabelt
TRUE/FALSE
the belt and parabelt does not respond to pure tones
true