auditory Flashcards
sound stimulus
occurs when the movements or vibrations of an object cause pressure changes in the air, water or any elastic medium that can transmit vibrations
condensation
- diaphragm of the speaker moves out,
- pushes the surrounding air molecules together
- slight increase in the density of molecules near the diaphragm.
- local increase in the air pressure above atmospheric pressure.
Rarefaction
- When the speaker diaphragm moves back in, air molecules spread out to fill in the increased space
- The decreased density of air
- a slight decrease in air pressure.
Sound wave:
pattern of air pressure changes, which travels through air at 340 meters per second (and through water at 1,500 meters per second), is called a sound wave
A pure tone
single frequency tone with no harmonic content (no overtones). This corresponds to a sine wave eg. (whistle)
periodic tone
a tone that operates on waveform repeats
Complex tone
complex tones are made up of pure tones can be made up over one or more simple tones known as overtones
Higher harmonics:
pure tones with frequencies that are whole numbers, multiples of the fundamental
frequency
- the number of cycles per second that the pressure changes repeat (Hz) 1 Hz is one cycle per second
- humans can perceive frequencies ranging from about 20 Hz to about 20,000 Hz
pitch
- aspect of auditory sensation whose variation is associated with musical melodies
- property of speech (low-pitched or high- pitched voice) and other natural sounds.
- most closely fundamental frequency (the repetition rate of the sound wave- form).
- Low fundamental frequencies are associated with low pitches (like the sound of a tuba),
- high fundamental frequencies are associated with high pitches (like the sound of a piccolo).
Tone height
the perceptual experience of increasing pitch that accompanies increases in a tone’s fundamental frequency
same tone chroma
notes with the same letter sound similar because they have the same tone chroma.
- Notes with the same chroma have fundamental frequencies that are separated by a multiple of two. Thus, A1 has a fundamental frequency of 27.5 Hz, A2’s is 55
- doubling of frequency for each octave results in similar perceptual experiences.
octave
Every time we pass the same letter on the keyboard, we have gone up an interval called an octave.
Loudness and Level Loudness:
perceptual quality most closely related to the level or amplitude of an auditory stimulus, which is expressed in decibels.
humans are most sensitive at
at frequencies between 2,000 and 4,000 Hz, which happens to be the range of frequencies that is most important for understanding speech.
Auditory response area:
threshold of hearing
The light green area above the audibility curve is called threshold of hearing
we can hear tones that fall within this area
threshold of feeling
The upper boundary of the auditory response area is the curve marked “threshold of feeling.” Tones with these high amplitudes are the ones we can “feel”; they can become painful and can cause damage to the auditory system.
what happens between the audibility curve and the threshold of feeling?
each frequency has a threshold or “baseline”—the decibels at which it can just barely be heard, as indicated by the audibility curve—and loudness increases as we increase the level above this baseline.
red equal loudness curves
indicate the sound levels that create the same perception of loudness at different frequencies.
- Present a standard pure tone of one frequency and level and having a listener adjust the level of pure tones with frequencies across the range of hearing to match the loudness of the standard.
timbre
- The quality that distinguishes between two tones that have the same loudness, pitch and duration but sounds different.
- depends on both the tone’s steady state harmonic structure and on the time course of the attack and decay of a tone’s harmonics
pinnae
Sound waves first past through –> pinnae: structures that stick out from the outsides of the head (part of the ear we don’t need)
Auditory canal:
a tubelike recess (3cm in adults) and protects the delicate structures of the middle ear
- enhances the intensities of some sounds –> resonance: in auditory canal, when soundwaves that are reflected back from the closed end of the auditory canal interact with sound waves that are entering the canal = reinforces some of the sound frequencies
resonant frequency
the frequency that is reinforced the most is called the resonant frequency of the canal
wax
- protects the tympanic membrane, or eardrum (end of the canal)
- keeps this membrane and structures in the middle ear at a relatively stable temperature
middle air
- small cavity (2 cubic centimetres in volume that separates the outer and inner ears
- this cavity contains ossicles, the 3 smallest bones in the body
malleus
is set into vibration by the tympanic membrane to which is is attached
transmits vibrations to incus
incus
anvil, transmits vibrations to stapes (stirrup)
stapes
the stapes then transmits vibrations to the inner ear by pushing on the membrane covering the oval window
muscles of the middle ear
- attached to the ossicles, and at very high sound levels they contract to dampen the ossicles vibration
- reduces the transmission of low-frequency sounds and helps to prevent intense low-frequency components from interfering with our perception of high frequencies.
- prevent our own vocalizations, and sounds from chewing, from interfering with our perception of speech from other people
inner ear
liquid-filled cochlea,
The Scala vestibuli (top/upper half), Scala tympani (bottom/bottom half) and are separated by cochlear partition.
organ or corti
membranes
cochlea partition
contains the structures that transform the vibrations inside the cochlea into electricity. (contains the organ of corti)
organ of Corti
which contains the inner and outer hair cells, and cilia; the receptors for hearing
- basilar membrane & tectorial membrane
cilia
thin processes that protrude from the tops of the hair cells, which bend in response to pressure changes
hair cells
- contains one row of inner hair cells and about three rows of outer hair cells
- The cilia of the tallest row of outer hair cells are embedded in the tectorial membrane and the cilia of the rest of the outer hair cells and all of the inner hair cells are not
vibrations that move the hair (the chain of events)
air goes through pinnae –> goes through tympanic membrane –> ossicles –> oval window –> back and forth motion of the oval window transmits vibrations –> inside the cochlea –> sets the basilar membrane into motion –> it sets the organ of Corti into an up-and-down vibration and it causes the tectorial membrane to move back and forth –> - The movement of the tectorial membrane causes the cilia of the outer hair cells that are embedded in the membrane to bend.
Bending hair causes electrical signals (transduction)
the movement of the hair cell cilia causes an electrical change in the hair cell
- when the cilia are bent to the right, the tip links are stretched and ion channels are opened (positively charged potassium ions (K+) enter the cell causing the interior of the cell to become more positive
- when the cilia move to the left the tips slacken and the channels close
- back-and-forth bending of the hair cells causes alternating bursts of electrical signals (when the cilia bend in one direction) and no electrical signals (when the cilia bend in the opposite direction).
- The electrical signals in the hair cells result in the release of neurotransmitters at the synapse separating the inner hair cells from the auditory nerve fibres and cause these auditory nerve fibres to fire
Bekesy’s place theory
- This explanation of the physiology of pitch perception
- based on the relation between a sound’s frequency and the place along the basilar membrane that is activated.
- Because the place of maximum vibration depends on frequency, this means that basilar membrane vibration effectively functions as a filter that sorts tones by frequency
- low frequencies cause maximum activity at the apex
- high frequencies cause maximum activity at the base.
DID THIS BY:
- Direct observation of the basilar membrane in cadavers.
- Building a model of the cochlea using the physical properties of the basilar membrane.
basilar membrane’s vibration as a traveling wave,
measurements showed that most of the membrane vibrates, but that some parts vibrate more than others.
Indicates the point of maximum displacement of the basilar membrane – Hair cells at this point are stimulated the most strongly leading to the nerve fibres firing the most strongly at this location. – Position of the peak is a function of frequency
faults and modified version of bekesys
- However Békésy’s broad vibration patterns was that his measurements were carried out on “dead” cochleas of animal and human cadavers.
- measured vibration in live cochleas, they showed that the pattern of vibration for specific frequencies was much narrower (causing a cochlea amplifier
cochlea amplifier
outer hair cells –> mechanical response of elongation and contraction pushes and pulls on the basilar membrane, which increases the motion of the basilar membrane and thus greatly sharpens the tuning of each place along the cochlea.
basilar membrane frequency analyser
- as the frequency increases, the place on the membrane that vibrates the most moves from the apex at the end of the cochlea toward the base at the oval window.
- basilar membrane vibration effectively functions as a filter that sorts tones by frequency.
filtering action is reflected by the following three characteristics of tuning curves: (1) the neurons respond best to one frequency; (2) each frequency is associated with nerve fibers located at a specific place along the basilar mem- brane, with fibres originating near the base of the cochlea having high characteristic frequencies and those originating near the apex having low characteristic frequencies; (3) the curves become wider at higher frequencies.
phase locking volley theory
- Firing bursts happen at or near the peak of the sine-wave stimulus. – Thus, they are “locked in phase” with the frequency of the stimulating tone wave
- Groups of fibers fire with periods of silent intervals creating a pattern of firing.
- Place coding is effective for the entire range of hearing.
- Temporal/periodicity coding with phase locking is effective up to 4,000 Hz.
the pathway to the brain
The auditory nerve fibres carry the signals toward the auditory receiving area in the cortex
-The cochlear nucleus –> superior olivary nucleus in the brain stem –> inferior colliculus in the midbrain–> medial geniculate nucleus in the thalamus.
the pathway to the brain
The auditory nerve fibres carry the signals toward the auditory receiving area in the cortex
- The cochlear nucleus –> superior olivary nucleus in the brain stem –> inferior colliculus in the midbrain–> medial geniculate nucleus in the thalamus.
- From the medial geniculate nucleus, fibres continue to the primary auditory cortex (, A1) in the temporal lobe of the cortex.
and then travel to other cortical auditory areas (1) the core area, which includes the primary auditory cortex (A1) and some nearby areas; (2) the belt area, which surrounds the core, and (3) the parabelt area
the core area
Simple sounds cause activation in the core area.
Belt and parabelt areas
activated in response to more complex stimuli made up of many frequencies.
anterior belt area
- neurons in anterior area of the belt respond to more complex sounds (monkey calls, vocalizations recorded from monkeys in the jungle)
- involved in identifying complex sounds.
- cooling technique –> deactivates the anterior belt and disrupts cat’s ability to distinguish b/w two timing patterns of sound
what auditory pathway, which extends from the anterior belt to the temporal lobe and the frontal cortex
posterior belt
involved in localising sounds
where auditory pathway, which extends from the posterior belt to the parietal lobe and the frontal cortex.
A1 is involved in pitch perception
fMRI measures the response to stimuli associated with pitch-evoking stimulus (Complex tone) and a noise stimulus –> both were (frequency-matched)
- areas in A1; core, belt, and parabelt areas in the monkey; and corresponding areas exist in humans and some nearby areas, that responded more to the pitch-evoking stimulus (anterior auditory cortex)
- resolved harmonics cause a large response in the areas that respond best to the pitch stimulus strengthens the
- Tonotopic maps are found in A1
- Research on stroke patients and marmosets provided support for the link between perception and physiological response in A1 –> cortical neurons, responded only to stimuli associated with the 182-Hz tone, associated with a specific pitch.
For this reason, Bendor and Wang called these neurons pitch neurons
auditory space
surrounds an observer and exists wherever there is sound
auditory localisation
The locating of sound sources in auditory space is called auditory localization.
auditory coordinates
Azimuth coordinates - position left to right
Elevation coordinates - position up and down
Distance coordinates - position from observer
people can localize sounds
- Directly in front of them most accurately
- To the sides and behind their heads least accurately.
Binaural cues
use information reaching both ears to determine the azimuth (left–right position) of sounds.
- The two binaural cues are interaural level difference and interaural time difference.
- Sounds that are off to the side are louder at one ear than the other and reach one ear before the other.
- Processing of interaural disparity cues occurs in the superior olivary complex (SOC) - first site of binaural interaction
Interaural time difference (ITD)
- difference between the times sounds reach the two ears
- When distance to each ear is the same, there are no differences in time.
- When the source is to the side of the observer, the times will differ.
- If the source is located directly in front of the listener, at A, the distance to each ear is the same; the sound reaches the left and right ears simultaneously, so the ITD is zero.
- However, if a source is located off to the side, at B, the sound reaches the right ear before it reaches the left ear.
- Thus ITD (which works for low frequencies)
- ITD is the most important binaural cue for most listening situations
Interaural level difference (ILD)
- Interaural level difference (ILD) is based on the difference in the sound pressure level (or just “level”) of the sound reaching the two ears.
- A difference in level between the two ears occurs because the head is a barrier that creates an acoustic shadow, reducing the intensity of sounds that reach the far ear.
- This reduction of intensity at the far ear occurs for high-frequency sounds, but not for low-frequency sounds
- For this reason, the ILD is an effective cue for location only for high-frequency sounds.
the cone of confusion
- While the time and level differences provide information that enables people to judge location along the azimuth coordinate, they provide ambiguous information about the elevation of a sound source.
Monaural Cue for Localization
- another source of information is needed to locate sounds along the elevation coordinate
- provided by a monaural cue—depends on information from only one ear.
- The primary monaural cue for localization is called a spectral cue
spectral cue
localization is contained in differences in the distribution (or spectrum) of frequencies that reach each ear from different locations.
- sound stimulus enters the auditory canal, it is reflected from the head and within the various folds of the pinnae
The effect of this interaction with the head and pinnae because differences in the way the sounds bounce around within the pinna create different patterns of frequencies for the two locations
method and results of Hofmann et al.’s “artificial pinnae” research
- pinnae for determining elevation has been demonstrated by showing that smoothing out the nooks and crannies of the pinnae with molding compound makes it difficult to locate sounds along the elevation coordinate
- After measuring initial performance, Hofman fitted his listeners with molds that altered the shape of the pinnae and therefore changed the spectral cue.
- localization performance is poor for the elevation coordinate immediately after the mold is inserted, but locations can still be judged at locations along the azimuth coordinate.
- Hofman continued his experiment by retesting localization as his listeners continued to wear the molds –> performance improved, until by 19 days localization had become reasonably accurate. Apparently, the person had learned, over a period of weeks
The Jeffress Neural Coincidence Model
- Narrowly tuned ITD neurons
- proposes a circuit that contains a series of ITD detectors, each tuned to respond best to a specific ITD.
- ITD will be indicated by which ITD neuron is firing –> This has been called a “place code” because ITD is indicated by the place (which neuron) where the activity occurs.
- coincidence detectors, because they only fire when both signals coincide by arriving at the neuron simultaneously
- tuning curves that are predicted by the Jeffress model, because each neuron responds best to a specific ITD and the response drops off rapidly for other ITDs.
The place code is for narrow tuning curves, works for owls and other birds, but the situation is different for mammals.
broad ITD Tuning Curves in Mammals
- the gerbil curve is much broader than the owl curve. In fact, the gerbil curve is so broad that it extends far outside the range of ITDs that are actually involved in sound localisation, indicated by the light bar
- coding for localisation is based on broadly tuned neurons in mammals
- there are broadly tuned neurons in the right hemisphere that respond when sound is coming from the left and broadly tuned neurons in the left hemisphere that respond when sound is coming from the right.
- The code for mammals is a population code because the ITD is determined by the firing of many broadly tuned neurons working together.
auditory scene
The array of sound sources at different locations in the environment
auditory scene analysis
the process by which the stimuli produced by each source are separated is called auditory scene analysis
auditory grouping
- Onset time - sounds that start at different times are likely to come from different sources
- Location - a single sound source tends to come from one location and to move continuously
- Similarity of timbre and pitch - similar sounds are grouped together
- Proximity in time - sounds that occur in rapid succession usually come from the same source
Auditory continuity - sounds that stay constant or change smoothly are usually from the same source
the precedence effect
where sound appears to originate from the lead speaker, is called the precedence effect because we perceive the sound as coming from the source that reaches our ears first
- even though the number called out by the butcher first reaches the listener’s ears directly and then is followed a little later by sound arriving along the indirect path, we hear it just once.
-The precedence effect governs most of our indoor listening experience. In small rooms, the indirect sounds reflected from the walls have a lower level than the direct sound and reach our ears
direct sound
sound that reaches the listener’s ears straight from the source
• When a listener is outside, most sound is direct;
indirect sound
sound that is reflected off of environmental surfaces and then to the listener
however inside a building, there is direct and indirect sound.
What is reverberation time
The amount and duration of indirect sound produced by a room.
precedence experiment
Experiment by Litovsky et al.
• Listeners sat between two speakers: a lead
speaker and a lag speaker.
• When sound comes from the lead speaker
followed by the lag speaker with a long
delay, listeners hear two sounds.
• When the delay is decreased to 5 - 20 msec,
listeners hear the sound as only coming from
the lead speaker - the precedence effect.
Factors that affect perception in concert
halls
– Reverberation time - the time is takes sound
to decrease by 1/1000th of its original
pressure (i.e., by 60dB)
>If it is too long, sounds are “muddled.”
>If it is too short, sounds are “dead.”
>Ideal times are around TWO SECONDS
Factors that Affect Perception in Concert
Halls
Reverberation time: 2 seconds
intimacy time: 20 ms
bass ratio: high bass ratios
spacious factor: high spaciousness
Intimacy time
time between when sound
leaves its source and when the first reflection
arrives
bass ratio
ratio of low to middle frequencies reflected from surfaces
spaciousness factor
fraction of all the sound received by listener that is indirect
