8 Flashcards
What is the physical definition of sound
Pressure changes in the air
what is the perceptual definition of sound
The experience we have when we hear
How does a sound stimulus occur?
when the vibrations of an object cause pressure changes in air, water, or any other elastic medium
What is a pure tone?
a simple kind of sound wave
* air pressure occur in a pattern described by a sine function
* can be described by its amplitude and frequency
How can a vibration be described?
by its frequency and amplitude
What is the amplitude?
difference in pressure between high an dlow peaks of the sound wave
Larger amplitude -> louder sound
use decibel (dB) as unit
What is frequency?
- the number of cycles per second that the change in pressure repeats
- higher frequencies -> higher pitches
- measured in Hz, 1Hz = 1 cycle per second
What is complex tone
- more complex waveforms than pure tone’s sine-wave pattern of pressure change
- made up of multiple pure tones (sine waves) added together
- what you find in the environment
What are periodic waveforms?
waveforms that repeat over time
both pure and some complex tones are periodic waveforms
What is fundamental frequency of a tone?
the repetition rate
What role do pure tones play in complex tones?
- many pure tones add up and make a complex tone
- each pure tone is called a harmonic of the tone
- the pure tone with the lowest frequency determines the fundamental frequency and is usally called the first harmonic
- higher harmonics are multiples of the fundamental frequency (2, 3, 4x multiples etc)
What is frequency spectra?
- another way to represent the harmonic components of a complex tone
- horizontal axis is frequency
- the position of each line on the horizontal axis indicates the frequency of each harmonic
- The height of the line indiates the harmonic’s amplitude
What are the 2 ways to represent the harmonic components of a complex tone?
- waveforms
- frequency spectra
What is loudness determined by?
amplitude
How can the relationship between level in dB (physical) and loudness (perceptual) be estimated?
stevens power law
What is the audibility curve
- a curve that demonstrate the hearing thresholds across the frequency range
- indicates the threshold for hearing vs frequency
- green area is called the auditory response area (tones we can hear)
- red area are tones we cant hear
- yellow area are tones that can result in pain
- blue line is the threshold of feeling = tones w high amlitudes are the ones we can feel, they can become painful and damaging
- red line is the equal loudness curves = sound levels that create the same perception of loudness at diff frequency
- green line = threshold of hearing
what is pitch?
- the property of auditory sensation which can be ordered on a musical scale
- related to (fundamental) frequency
How is pitch related to fundamental frequency?
Low fundamental frequency -> low pitch
High with high
What do notes with the same letter (A1 and A2) have?
they sound similar so we say they have the same tone chroma
What is an octave?
if we pass the same letter on the keyboard, we have gone up an interval
What happens to the pitch if you double the frequency?
increases the pitch by one octave
so notes with the same letter have frequencies that are multiples of each other
What are the 3 parts of the ear?
outer, middle, inner
the pressure changes are transduced to electrical signals and sent to the brain
What are 2 parts of the outer ear?
pinna and auditory canal
What does the pinna do?
helps us determine the location of sounds
* is the easiest part of the ear we could do without
Whats the auditory canal?
- a 3cm long tube like structure
- protects the delicate structures of the middle ear (e.g. tympanic membrane)
- enhance the intensities of some sound by means of resonance (when sound waves are reflected back from the closed end of the auditory canal and interacts with the sound waves entering the canal)
What is the midde ear?
- a 2 cubic cm small cavity
- seperates inner from outer ear
- contains 3 ossicles (malleus, incus, stapes)
What are the function of the 3 ossicles?
- act as a signal amplifier
- the outer and middle ear are filled with air but inner ear contains liquid denser than the air
- so pressure changes in the air transmit poorly into the liquid
- so the ossicles can amplify the vibration for better transmission to the fluid
What structures are in the inner ear?
- cochlea
- scala vestibuli
- scala tympani
- cochlear partition
What is the cochlea
fluid-filled snail like structure that recieves vibration from the stapes
What is scala vestibuli
upper half of the cochlea
What is scala tympani
lower half of the cochlea
what is cochlear partition
seperates the scala vestibuli and scala tympani
extends along almost the entire legnth of the cochlea from base to apex
What is the organ of corti
- a structure in the cochlear partition
- contains hair cells (receptors for hearing)
- transduction occurs here
Which interaction causes tranduction to take place
- 3 key components
- tectorial membrane
- inner and outer hair cells (1:3)
- basilar membrane
How does transduction happen
- oval window transmits the vibration to the basilar membrane and tectorial membrane
- the sterocilia (small processes at the tip of hair cells) of the hair cells bend to one direction (stereocilia is embedded in the tectorial membrane)
- causes tip links to stretch and this opens the ion channels in the membrane of the stereocilia
- K+ follow into the cell and an electrical signal is generated
- if the sterocilia bends in the other direction, the ion channels closed, and no electrical signal
What does the bending of stereocilia follow?
the increase and decreases of the pressure of a pure tone
pressure increases -> stereocilia bend to the right -> hair cell is activates -> auditory nerve fiber firing
no firing in other direction
This means that auditory nerve fibers fire in synchrony with the rising and falling pressure of the pure tone.
What are the roles of inner hair cells?
transduce the vibrations into electronical signals that are sent to the cortex via the auditory neural fibers
What are the major roles of outer hair cells?
- ion flow in outer hair cells causes mechanical changes inside the cell that causes the cell to expand and contract
- become elongated when the stereocilia bend in one direction and contract in the other
- this mechanical response push and pulls on the basilar membrane, which increases the motion off it and sharpens its response to specific frequencies
How is frequency information presented in the cochlea?
different frequncies make different locations on the basilar membrane vibrate the most
Near apex: vibrates most for 25Hz tone (low freq)
near base: vibrates most for a 1600Hz tone (high freq)
there is a tonotopic map
What is the A1?
primary auditory cortex in the temporal lobe and receives basic auditory input
Does A1 have a tonotopic map?
yes
different location sensitive to diff frequencies
What pathway of aud?
ventral pathway
from anterior portion of A1 to the PFC
responsible for identifying sounds
Where pathway for aud?
dorsal pathway
from posterior portion of A1 to the parietal and PFC
responsible for locating sounds
