Problem 7 - DONE Flashcards
auditory perception
perceptual process of hearing
- environmental stimulus
- transformation into sound stimulus
- pressure changes (trigger a sequence of events)
- representation within ears
- -> receptors = hair cells = structures that receive stimuli - neural signals are sent to the brain
- signals lead to perception
physical definition of sound
= sound is pressure changes in the air or other medium
–> ‘sound stimulus’
perceptual definition of sound
= sound is the experience we have when we hear
–> ‘sound perception’
sound stimulus
= stimuli for hearing = pressure changes in the air
- -> occurs when movements/ vibrations of object cause pressure changes
- -> in air, water, any other elastic medium that surrounds object
sound wave
= pattern of alternating high- and low-pressure regions in the air
- -> neighbouring air molecules affect each other
- condensation = push the surrounding air molecules together
- result: slight increase in density of molecules near object
- -> increased density = local increase in air pressure above atmospheric pressure
- rarefaction = air molecules spread out to fill in increased space
- result: decreased density of air molecules
- -> decreased density = slight decrease in air pressure
pure tones
= simple kind of sound waves
- -> sine wave
- rare in environment
- fundamental building blocks of sounds
frequency
= number of cycles per second that the pressure changes repeat
–> associated with perceptual pitch
=> the higher the frequency –> the higher the pitch
- measured in hertz (Hz)
- -> 1 Hz = 1 cycle per second
- humans can perceive 20 Hz - 20,000 Hz
amplitude
= size of pressure change = indicate difference in pressure between high and low peaks of sound wave
–> associated with perceptual loudness
=> the higher the amplitude –> the louder
- measured in decibel (dB) (= unit which converts large range of sound pressures into a more manageable scale)
- range in environment: extremely large (whisper to jet taking off)
complex tones
- sounds in environment = more complex than sine wave
- made up of a number of pure tone components added together
1. fundamental frequency = first harmonic = lowest frequency of periodic tone (= waveform repetition) - provides the strongest audible reference
2. harmonics = components of a complex tone; pure tones with frequencies that are whole-number multiples of fundamental frequency
frequency spectra
= harmonic spectra = represent harmonic components of complex tone
- -> indicate complex tone’s fundamental frequency + harmonics
- x-axis: frequency
- y-axis: amplitude
physical aspects
- frequency
- amplitude
perceptual aspects
- threshold
- loudness
- pitch
- timbre
threshold
= smallest amount of sound energy that can barely be detected
loudness
= perceived intensity of a sound that ranges from ‘just audible’ to ‘very loud’
- related to amplitude + frequency
- expressed in decibels
- -> magnitude estimation: determines relationship between amplitude (physical) + loudness (perceptual
audibility curve
= indicates threshold for hearing vs. frequency
- auditory response area = area within we can hear the tones
- -> upper boundary: threshold of feeling
- equal loudness curve = indicate sound levels that create the same perception of loudness at different frequencies
pitch
= perceiving the tone as ‘high’ or ‘low’ (= tone height)
- related to fundamental frequency (spacing of harmonics, repetition of waveform)
- -> low fundamental frequency: low pitch
- -> high fundamental frequency: high pitch
- property of speech, music
- can’t be measured in physical way
- -> tone height = perceptual experience of increasing pitch that accompanies increases in tone’s fundamental frequency
- -> tone chroma = notes with the same tone; notes separated by octave have same chroma
pitch
effect of missing fundamental
= effect in which the pitch remains the same, even if fundamental/other harmonics are removed
- periodicity pitch = pitch that we perceive in tones that have harmonics removed
- -> pitch is determined by period/rate of sound waveform
timbre
= quality that distinguishes between two tones that have the same loudness, pitch, and duration, but still sound different
- related to harmonic structure of a tone
- changes when remove harmonics
- depends on time course of attack + decay
- -> attack = buildup of sound at the beginning of the tone
- -> decay = decrease in sound at the end of the tone
journey throughout ear
- sound enters outer ear
- vibrations at tympanic membrane are transmitted to structures middle ear
- vibration by movement of stapes against oval window sets up fluid vibration in inner ear
4a. vibration in cochlea liquid sets basilar membrane into motion
4b. sets organ of Corti into an up-and-down vibration
4c. causes back/forward motion in tectorial membrane
4d. cilia of hair cells bend (outer hair cells)
- -> deliver sound stimulus to receptors
- -> transduction: from pressure changes into electrical signals
- -> processes electrical signals to indicate qualities of sound source (pitch, loudness, timbre, location)
outer ear
= consists of pinnae and auditory canal
- pinnae = structures that stick out from the sides of the head
- -> determining location (elevation)
- auditory canal = tubelike structure, about 3 cm long in adult; protects delicate structures of middle ear from outside world
outer ear
functions of auditory canal
- protective function
- protects eardrum
- helps keep membrane/structures at relative constant temperature
- -> eardrum = tympanic membrane (at the end of the auditory canal) - enhancing intensities of some sounds by resonance
- principle of resonance = in auditory canal; when sound waves are reflected back from the closed end of auditory canal interact with sound waves entering the canal
- -> resonant frequency = frequency reinforced the most by resonance (determined by length of canal)
- -> slight amplifying effect
middle ear
= other side of tympanic membrane; small cavity, about 2 cubic centimetres in volume; separates outer and inner ears
- ossicles
- middle-ear muscles
middle ear
ossicles
= three smallest bones in body
- malleus = hammer; first of the ossicles; attached to tympanic membrane
- set into vibration by tympanic membrane
- transmits vibrations to incus - incus = anvil
- receives vibrations from malleus
- transmits its vibrations to stapes - stapes = stirrup;
- receives vibrations from incus
- transmits its vibrations to inner ear by pushing on membrane covering the oval window
middle ear
functions of ossicles
mismatch:
- outer ear + middle ear: filled with air (low density)
- inner ear: watery liquid (high density)
–> problem: pressure changes in air are transmitted poorly to much denser liquid
=> less than 1% of vibrations would be transmitted
- solution:
(1) concentrating vibration of large tympanic membrane onto much smaller stapes –> increases pressure by a factor of about 20
(2) being hinged to create a lever action: effect similar to pushing down on the long end of the board to lift a heavy weight on the short end
middle ear
middle-ear muscles
= smallest skeletal muscles in the body; attached to ossicles
- very high sound levels: contract to dampen ossicles’ vibration
- -> reduce transmission of low-frequency sounds
- -> prevent intense low-frequency components from interfering with our perception of high frequencies
inner ear
- cochlea = snail-like structure
- -> liquid-filled; liquid is set into vibration by movement of stapes against oval window
- -> main structure of inner ear
- -> cochlear partition: separates scala vestiboli + scala tympani
- contains organ of Corti
- -> contains hair cells
- -> sits on basilar membrane (plays important role in activating hair cells)
hair cells
= receptors of hearing
- extend from one end of cochlea to the other
two types:
1. inner hair cells: one row of these
–> transduction of sound pressure to the brain (bottom-up)
2. outer hair cells: three rows of these
–> modulate/fine-tune responses of inner hair cells (top-down = process signals from the brain to the cochlea)
- tallest row of cilia is in contact with tectorial membrane
–> cilia = thin processes extending from top of the hair cells; bend in response to pressure changes
- tectorial membrane is arching over hair cells
–> play important role in activating hair cells
vibrations in inner ear
- back and forth motion of oval window: transmits vibrations to liquid inside cochlea
- -> sets basilar membrane into motion
- result:
- -> sets organ of Corti into an up-and-down vibration
- -> causes tectorial membrane to move back and forth
- motion of tectorial membrane:
- -> slides back and forward just above inner hair cells
- result: cilia of hair cells bend
- -> outer hair cells in contact with tectorial membrane
transduction for hearing
= pressure waves become transformed into electrical signals
- involves ion flow
- occurs when cilia of hair cells bend back-and-forth
=> alternating bursts of electrical signals (1) vs. no electrical signals (2)
(1) movement in one direction (increase in pressure): tip links stretch –> tiny ion channels in membrane of cilia open (behave like trapdoors) –> positively charged potassium ions flow into cell
- tip links = structures in inner ear
(2) movement in other direction (decrease in pressure): tip links slacken —> ion channels close —> no electrical signals are generated
how are the electrical signals created by hair cells related to frequency of a tone?
- auditory nerve fibres fire in synchrony with rising/falling pressure of a tone:
(1) pressure increases —> cilia bend to the right —> the hair cell is activated —> attached auditory nerve fibres will tend to fire
(2) pressure decreases —> cilia bend to the left —> no firing occurs - -> phase locking
phase locking
= firing at the same place in sound stimulus
–> when fibre fires: fires at the same time in a sound stimulus
(explains why removing of an harmonic won’t change the pitch)
fourier analysis
= takes complex sounds and decomposes it into its different frequencies
- what cochlea automatically does
- -> from representation of sound in terms of pressure level and time –> to representation in terms of frequencies and amplitude
neural frequency tuning curve
= maps different frequencies along cochlea
- -> measure sound level needed to cause neurone to increase firing
- -> characteristic frequency (CF) = frequency to which a particular auditory nerve fiber is most sensitive; lowest point on the curve
place code
= different frequencies are signalled by activity in neurones that are located at different places in auditory system
–> neurones that are neighbouring in auditory system respond to neighbouring frequencies
=> tonotopy
primary central auditory pathway
(1) cochlear nucleus = brain stem nucleus
- where afferent auditory nerve fibres first synapse
(2) superior olivary nucleus = brain stem region
- where inputs from both ears converge
(3) inferior colliculus = midbrain nucleus
(4) medial geniculate nucleus (MGN) = thalamus
- relays auditory signals to temporal cortex
- receives input from auditory cortex (feedback)
(5) auditory cortex
=> SONIC MG —> SON = superior olivary nucleus; IC = inferior colliculus; MG = medial geniculate nucleus
primary auditory cortex (A1)
= in temporal lobes of brain; responsible for processing acoustic information
- belt area = region of cortex; directly adjacent to A1
- -> inputs: from A1
- -> where neurones respond to more complex characteristics of sounds
- parabelt area = region of cortex; lateral and adjacent to belt area
- -> where neurons respond to more complex characteristics of sounds + input from other senses
tonotopic organisation
= neurones responding to different frequencies are organised in order of frequency
- -> reflects properties of transduction + importance of frequency composition of sounds
cochlea: - -> base (closest to middle ear): higher frequency for action potential
- -> the more to apex, the lower the frequencies
hearing loss
- typically involves elevation of sound thresholds
- can be due to impairment in any structure of auditory processes
conductive hearing loss
= dysfunction in outer + middle ear
–> when middle-ear bones lose ability to freely convey vibrations from tympanic membrane to oval window
causes:
- otitis media = inflammation of middle ear
–> middle ear fills with mucus
solutions:
- amplification of sound
prespycusis
= hearing loss greatest at high frequencies
–> hair cell damage
causes:
- cumulative effects over time of noise exposure,
- ingestion of drugs that damage hair cells
- age-related degeneration
noise-induced hearing loss
–> degeneration of hair cells
–> damage of organ of Corti (often observed)
causes:
- loud noises
–> seriousness depends on level of sound intensity + duration of exposure
sensorineural hearing loss
–> inner ear/sensory organ (= cochlea)
–> hair cells/auditory nerves
solutions:
- cochlear implant (= micro-electrode that stimulates directly the auditory nerve)
- auditory brain stem implant = prosthesis consisting of a microelectrode that directly stimulates one of auditory processing centers of brainstem
hidden hearing loss
= makes it harder to hear sounds when there is background noise
–> normally no effect on person’s ability to hear sounds
time code
= different frequencies are signalled by timing of neural responses;
- phase locking
- -> works until 1000 Hz (limitation to how fast neurones can fire)
- -> volley principle (population code) = phase lock of several neurones are added together
- -> multiple neurones can provide temporal code for frequency if each neurone fires at distinct point in period of a sound wave but does not fire on every period
- -> works until 4000 Hz
