Topic 9: Hearing Flashcards
sound
physical phenomenon
pressure changes in air or another medium
caused by vibrating object
condensation
rarefaction
air molecules are pushed together
air molecules are spread out
alternating patterns of compressed and non-compressed air
pure tones
complex tones
generated by tuning for or computer
sound is described by set of pure tones
can be made by summing pure tones, tones represented by frequencies not time
sine wave
frequency
amplitude
- sinusodal cahnge in air pressure
- number of cycles per second (Hertz)
- magnitude of air pressure changes (dB), 20 x log`
spectrogram
white noise
calculate energy at each frequency, straight lines are same frequency at each time point
red = high energy black = no energy
-random frequencies that change randomly, evenly dispersed over spectrogram
loudness
threshold of feeling
perceptual quality most closely related to level or amplitude of auditory stimulus
- loudness will vary with frequency
- hearing is painful, small but noticeable frequency differences
pitch
perceptual quality we describe as high and low
pitch is related to fundamental frequency
tone height
tone chroma
generally goes up with fundamental frequency
notes whose fundamental freuqnecy are multiples of 2 have same chroma (high and low C)
timbre
quality of sound
difference between 2 tones that have same loudness and pitch but sound different - 2 instruments
shepard-risset glissando
constant spectrum
- continuously goes down
- perceptually changes but frequencies are stable, closely spaced harmonics
pinna
auditory canal
eardrum
OUTER EAR
- helps focus sound towards ear canal (direction of sound)
- protects ear drum, enhances frequencies of 1000-5000 hz due to resonance
- transmits sound as vibration to middle ear
middle ear
MIS
sound pressure changes causes eardrum vibration
malleus = hammer incus = anvil stapes = stirrup
middle ear purpose and mechanisms
- amplifies sound by a factor of 10-50 from air pressure in outer ear to liquid pressure in inner ear
- concentrates pressure from large eardrum to small stapes footplate
middle ear muscles
stapedius
- tensor tympani
- contracts to mute movement of tapes so auditory system isnt overwhelmed
semicircular ducts
cochlea
involved in balance and eq
coiled structure and contains sensory receptors for sound
basliar membrane
tip links
sounds transmitted to auditory nerve, pressure waves in cochlea cause baslia membrane to move up and down
- bends cilia and causes ion (K+) channels to open, transduction
- Right = open, left = close
phase locking
movement of cilia follows changes in pressure
neurotransmitter release follows changes in pressure
place theory
location with peak displacement has highest firing rate by auditory nerve cells
location of max firing indicates frequency
percieved tone is based on where activity is along length of cochlea
cochlear amplifier
frequency representation
frequency tuning curve
outer hair cells change shape based on sound and amplify/focus motion of basliar membrane
- sound causes waves to travel along basliar membrane (closer to base for higher frequency)
- each auditory nerve cell responds to certain frequencies based on cochlear position
effect of missing fundamental
amplitude modulation
- pitch of C is same as A even without fundamental, no longer peak activity at same place despite same perceived pitch
- fluctuating amplitude of sound at a specific frequency, changes pitch perception despite same frequency of sound
temporal theory
timing or repetition rate of a sound is available even when fundamental is missing and with amplitude modulation
leads to phase locking
auditory pathway
ACSIMA1
auditory nerve cochlear nuclei - medulla superior olivary nucleus - pons inferior colliculus - midbrain medial geniculate nucleus - thalamus primary auditory cortex (A1)
external components cochlear implant
-microphone - transduces sound into electricity
-processor- analyzes sound into frequency bands, stimulates place specific activation of basliar membrane
transmitter- sends signals and power
internal components cochlear implant
- receiver - receives signals and power
- electrodes - stimulate different auditory nerves along length of cochlea
