Hearing: The Auditory System, Localisation, And Auditory Scene Analysis Flashcards
Define
Acoustic shadow
an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents, buildings, or sound barriers
Define
Additive synthesis
process of adding harmonics to create complex sounds
Define
Amplitude
the fluctuation or displacement of a wave from its mean value
Define
Amplitude modulation
the modulation of a wave by varying its amplitude, used especially as a means of broadcasting an audio signal by combining it with a radio carrier wave
Define
Amplitude-modulated noise
the detection of modulation versus the detection of modulation rate
Define
Aperiodic sounds
sound whose pattern does not repeat itself as do those of the periodic sounds
Define
Attack
changes occurring before the sound reaches its steady-state intensity
Define
Audibility curve
the relationship between the threshold of hearing for a pure tone, expressed in decibels sound-pressure level (dB SPL), and the frequency of the tone
Define
Auditory canal
canal leading from the opening of the external ear to the eardrum
Define
Auditory localisation
describes an organism’s ability to perceive the location of the source of a sound
Define
Auditory
falls between the audibility curve and and the. threshold for feeling
Define
Auditory scene analysis
a proposed model for the basis of auditory perception. This is understood as the process by which the human auditory system organizes sound into perceptually meaningful elements
Define
Auditory space
surrounds an observer and exists wherever there is sound
Define
Auditory stream segragation
the perceptual grouping of sounds, to form coherent representations of objects in the acoustic scene, and is a fundamental aspect of hearing and speech perception
Define
Azimuth
the direction of a celestial object from the observer, expressed as the angular distance from the north or south point of the horizon to the point at which a vertical circle passing through the object intersects the horizon.
Define
Basilar membrane
a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani.
Define
Bass ratio
ratio of low to middle frequencies reflected from surfaces
Define
Belt area
the secondary auditory cortex immediately surrounding the core
Define
Binaural cues
any difference in the sound arriving at the two ears from a given sound source (interaural difference) that acts as a cue to permit auditory localization
Define
Characteristic frequency
The frequency of a sound at which the threshold of a single fibre of an auditory nerve is lowest and to which it is therefore most responsive
Define
Cilia
the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance
Define
Cochlea
a spiralled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the oval window) to the apex (the top or center of the spiral)
Define
Cochlear amplifier
a positive feedback loop within the cochlea that amplifies the traveling wave
Define
Cochlear nucleus
the obligatory nucleus in which all ascending information from the cochlea forms synaptic connections with the auditory brain
Define
Coincidence detectors
the context of neurobiology is a process by which a neuron or a neural circuit can encode information by detecting the occurrence of temporally close but spatially distributed input signals
Define
Condensation
part of a sound wave where the density is higher than normal
Define
Decay
rate at which the music fades to silence
Define
Direct sound
sound that reaches the listener’s ears straight from the source
Define
Effect of the missing fundamental
Removal of the first harmonic in a sound with the same perceived pitch, but with a different timbre
Define
Event related potential
the measured brain response that is the direct result of a specific sensory, cognitive, or motor event
Define
First harmonic
another term for the fundamental frequency which sets the repetition rate
Define
Frequency
the number of occurrences of a repeating event per unit of time
Define
Frequency spectrum
display of harmonics of a complex sound
Define
Fundamental
the lowest frequency of a periodic waveform
Define
Fundamental frequency
the lowest frequency which is produced by the oscillation of the whole of an object, as distinct from the harmonics of higher frequency
Define
Hair cells
the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes
Define
Harmonic
a signal or wave whose frequency is an integral (whole-number) multiple of the frequency of some reference signal or wave
Define
Hertz (Hz)
the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second
Define
Incus
a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear
Define
Indirect sound
sound that is reflected off of environmental surfaces and then to the listener
Define
Inferior colliculus
the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex
Define
Inner hair cells
the sensory cells of the cochlea, are responsible for signal transduction
Define
Interaural level difference (ILD)
the difference in loudness and frequency distribution between the two ears
Define
Interaural time difference (ITD)
the difference in arrival time of a sound between two ears
Define
Intimacy time
time between when sound leaves its source and when the first reflection arrives
Define
Jeffress model
a neurocomputational model that explains how auditory systems can register and analyze small differences in the arrival time of sounds at the two ears in order to estimate the direction of sound sources in the azimuthal plane.
Define
Loudness
the subjective perception of sound pressure
Define
Malleus
a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum
Define
Medial geniculate nucleus
part of the auditory thalamus and represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC).
Define
Melody
a sequence of single notes that is musically satisfying; a tune.
Define
Middle ear
the portion of the ear internal to the eardrum, and external to the oval window of the inner ear
Define
Middle ear muscles
two muscles which serve a protective function in the middle ear; the tensor tympani and stapedius
Define
Monaural cue
relies on sounds reaching a single ear to constrain the set of possible sound sources
Define
Octave
the interval between one musical pitch and another with double its frequency
Define
Onset time
sounds that start at different times are likely to come from different sources
Define
Organ of Corti
the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses’ action potential.
Define
Ossicles
three bones in either middle ear that are among the smallest bones in the human body.
Define
Outer ear
the external portion of the ear, which consists of the auricle (also pinna) and the ear canal
Define
Oval window
a membrane-covered opening that leads from the middle ear to the vestibule of the inner ear
Define
Periodic sounds
sounds which repeats itself at regular intervals
Define
Periodicity pitch
Removal of the first harmonic in a sound with the same perceived pitch, but with a different timbre
Define
Phase locking
the mechanism by which the peripheral auditory system keeps track of the times of occurrence of the ongoing amplitude fluctuations in sounds
Define
Pinnae
the external part of the ear in humans and other mammals; the auricle
Define
Place theory
a theory of hearing that states that our perception of sound depends on where each component frequency produces vibrations along the basilar membrane
Define
Precedence effect
a binaural psychoacoustical effect. When a sound is followed by another sound separated by a sufficiently short time delay (below the listener’s echo threshold), listeners perceive a single auditory event
Define
Presbycusis
the loss of hearing that gradually occurs in most individuals as they grow older
Define
Primary auditory cortex (A1)
part of the temporal lobe that processes auditory information in humans and many other vertebrates
Define
Pure tone
a sound with a sinusoidal waveform; that is, a sine wave of any frequency, phase, and amplitude
Define
Rarefaction
reduction in the density of something, especially air or a gas
Define
Resolved harmonics
lower harmonics that are separated out in the cochlea (i.e., they excite distinct places on the basilar membrane)
Define
Resonance
the phenomena of amplification that occurs when the frequency of a periodically applied force is in harmonic proportion to a natural frequency of the system on which it acts
Define
Resonant frequency
a natural frequency of vibration determined by the physical parameters of the vibrating object
Define
Reverberation time
the time it takes sound to decrease by 1/1000th of its original pressure
Define
Scale illusion
an auditory illusion in which principles of grouping by frequency, proximity, and spatial location are put into conflict and in which frequency proximity wins out
Define
Sound
vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear.
Define
Sound pressure level (SPL)
the pressure level of a sound, measured in decibels (dB)
Define
Sound wave
a wave of compression and rarefaction, by which sound is propagated in an elastic medium such as air.
Define
Spaciousness factor
fraction of all the sound received by listener that is indirect
Define
Stapes
a small stirrup-shaped bone in the middle ear, transmitting vibrations from the incus to the inner ear.
Define
Subcortical structures
a group of diverse neural formations deep within the brain which include the diencephalon, pituitary gland, limbic structures and the basal ganglia.
Define
Superior olivary nucleus
a group of nuclei located in the brainstem near the junction of the pons and medulla. It is the first auditory relay after the cochlear nucleus on the way to the auditory cortex and is the major point at which information from the two ears is integrated.
Define
Tectorial membrane
an extracellular connective tissue that covers the mechanically-sensitive hair bundles of the sensory receptor cells in the inner ear.
Define
Temporal coding
a type of neural coding which relies on precise timing of action potentials or inter-spike intervals
Define
Timbre
the character or quality of a musical sound or voice as distinct from its pitch and intensity.
Define
Tip links
extracellular filaments that connect stereocilia to each other or to the kinocilium in the hair cells of the inner ear
Define
Tonality
the arrangement of pitches and/or chords of a musical work in a hierarchy of perceived relations, stabilities, attractions and directionality
Define
Tone height
perceptual experience of increasing pitch as tone’s frequency (wavelength increases)
Define
Tympanic membrane
a membrane forming part of the organ of hearing, which vibrates in response to sound waves. In humans and other higher vertebrates it forms the eardrum, between the outer and middle ear.
Definition
an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents, buildings, or sound barriers
Acoustic shadow
Definition
process of adding harmonics to create complex sounds
Additive synthesis
Definition
the fluctuation or displacement of a wave from its mean value
Amplitude
Definition
the modulation of a wave by varying its amplitude, used especially as a means of broadcasting an audio signal by combining it with a radio carrier wave
Amplitude modulation
Definition
the detection of modulation versus the detection of modulation rate
Amplitude-modulated noise
Definition
sound whose pattern does not repeat itself as do those of the periodic sounds
Aperiodic sounds
Definition
changes occurring before the sound reaches its steady-state intensity
Attack
Definition
the relationship between the threshold of hearing for a pure tone, expressed in decibels sound-pressure level (dB SPL), and the frequency of the tone
Audibility curve
Definition
canal leading from the opening of the external ear to the eardrum
Auditory canal
Definition
describes an organism’s ability to perceive the location of the source of a sound
Auditory localisation
Definition
falls between the audibility curve and and the. threshold for feeling
Auditory
Definition
a proposed model for the basis of auditory perception. This is understood as the process by which the human auditory system organizes sound into perceptually meaningful elements
Auditory scene analysis
Definition
surrounds an observer and exists wherever there is sound
Auditory space
Definition
the perceptual grouping of sounds, to form coherent representations of objects in the acoustic scene, and is a fundamental aspect of hearing and speech perception
Auditory stream segragation
Definition
the direction of a celestial object from the observer, expressed as the angular distance from the north or south point of the horizon to the point at which a vertical circle passing through the object intersects the horizon.
Azimuth
Definition
a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani.
Basilar membrane
Definition
ratio of low to middle frequencies reflected from surfaces
Bass ratio
Definition
the secondary auditory cortex immediately surrounding the core
Belt area
Definition
any difference in the sound arriving at the two ears from a given sound source (interaural difference) that acts as a cue to permit auditory localization
Binaural cues
Definition
The frequency of a sound at which the threshold of a single fibre of an auditory nerve is lowest and to which it is therefore most responsive
Characteristic frequency
Definition
the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance
Cilia
Definition
a spiralled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the oval window) to the apex (the top or center of the spiral)
Cochlea
Definition
a positive feedback loop within the cochlea that amplifies the traveling wave
Cochlear amplifier
Definition
the obligatory nucleus in which all ascending information from the cochlea forms synaptic connections with the auditory brain
Cochlear nucleus
Definition
the context of neurobiology is a process by which a neuron or a neural circuit can encode information by detecting the occurrence of temporally close but spatially distributed input signals
Coincidence detectors
Definition
part of a sound wave where the density is higher than normal
Condensation
Definition
rate at which the music fades to silence
Decay
Definition
sound that reaches the listener’s ears straight from the source
Direct sound
Definition
Removal of the first harmonic in a sound with the same perceived pitch, but with a different timbre
Effect of the missing fundamental
Definition
the measured brain response that is the direct result of a specific sensory, cognitive, or motor event
Event related potential
Definition
another term for the fundamental frequency which sets the repetition rate
First harmonic
Definition
the number of occurrences of a repeating event per unit of time
Frequency
Definition
display of harmonics of a complex sound
Frequency spectrum
Definition
the lowest frequency of a periodic waveform
Fundamental
Definition
the lowest frequency which is produced by the oscillation of the whole of an object, as distinct from the harmonics of higher frequency
Fundamental frequency
Definition
the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes
Hair cells
Definition
a signal or wave whose frequency is an integral (whole-number) multiple of the frequency of some reference signal or wave
Harmonic
Definition
the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second
Hertz (Hz)
Definition
a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear
Incus
Definition
sound that is reflected off of environmental surfaces and then to the listener
Indirect sound
Definition
the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex
Inferior colliculus
Definition
the sensory cells of the cochlea, are responsible for signal transduction
Inner hair cells
Definition
the difference in loudness and frequency distribution between the two ears
Interaural level difference (ILD)
Definition
the difference in arrival time of a sound between two ears
Interaural time difference (ITD)
Definition
time between when sound leaves its source and when the first reflection arrives
Intimacy time
Definition
a neurocomputational model that explains how auditory systems can register and analyze small differences in the arrival time of sounds at the two ears in order to estimate the direction of sound sources in the azimuthal plane.
Jeffress model
Definition
the subjective perception of sound pressure
Loudness
Definition
a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum
Malleus
Definition
part of the auditory thalamus and represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC).
Medial geniculate nucleus
Definition
a sequence of single notes that is musically satisfying; a tune.
Melody
Definition
the portion of the ear internal to the eardrum, and external to the oval window of the inner ear
Middle ear
Definition
two muscles which serve a protective function in the middle ear; the tensor tympani and stapedius
Middle ear muscles
Definition
relies on sounds reaching a single ear to constrain the set of possible sound sources
Monaural cue
Definition
the interval between one musical pitch and another with double its frequency
Octave
Definition
sounds that start at different times are likely to come from different sources
Onset time
Definition
the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses’ action potential.
Organ of Corti
Definition
three bones in either middle ear that are among the smallest bones in the human body.
Ossicles
Definition
the external portion of the ear, which consists of the auricle (also pinna) and the ear canal
Outer ear
Definition
a membrane-covered opening that leads from the middle ear to the vestibule of the inner ear
Oval window
Definition
sounds which repeats itself at regular intervals
Periodic sounds
Definition
Removal of the first harmonic in a sound with the same perceived pitch, but with a different timbre
Periodicity pitch
Definition
the mechanism by which the peripheral auditory system keeps track of the times of occurrence of the ongoing amplitude fluctuations in sounds
Phase locking
Definition
the external part of the ear in humans and other mammals; the auricle
Pinnae
Definition
a theory of hearing that states that our perception of sound depends on where each component frequency produces vibrations along the basilar membrane
Place theory
Definition
a binaural psychoacoustical effect. When a sound is followed by another sound separated by a sufficiently short time delay (below the listener’s echo threshold), listeners perceive a single auditory event
Precedence effect
Definition
the loss of hearing that gradually occurs in most individuals as they grow older
Presbycusis
Definition
part of the temporal lobe that processes auditory information in humans and many other vertebrates
Primary auditory cortex (A1)
Definition
a sound with a sinusoidal waveform; that is, a sine wave of any frequency, phase, and amplitude
Pure tone
Definition
reduction in the density of something, especially air or a gas
Rarefaction
Definition
lower harmonics that are separated out in the cochlea (i.e., they excite distinct places on the basilar membrane)
Resolved harmonics
Definition
the phenomena of amplification that occurs when the frequency of a periodically applied force is in harmonic proportion to a natural frequency of the system on which it acts
Resonance
Definition
a natural frequency of vibration determined by the physical parameters of the vibrating object
Resonant frequency
Definition
the time it takes sound to decrease by 1/1000th of its original pressure
Reverberation time
Definition
an auditory illusion in which principles of grouping by frequency, proximity, and spatial location are put into conflict and in which frequency proximity wins out
Scale illusion
Definition
vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear.
Sound
Definition
the pressure level of a sound, measured in decibels (dB)
Sound pressure level (SPL)
Definition
a wave of compression and rarefaction, by which sound is propagated in an elastic medium such as air.
Sound wave
Definition
fraction of all the sound received by listener that is indirect
Spaciousness factor
Definition
a small stirrup-shaped bone in the middle ear, transmitting vibrations from the incus to the inner ear.
Stapes
Definition
a group of diverse neural formations deep within the brain which include the diencephalon, pituitary gland, limbic structures and the basal ganglia.
Subcortical structures
Definition
a group of nuclei located in the brainstem near the junction of the pons and medulla. It is the first auditory relay after the cochlear nucleus on the way to the auditory cortex and is the major point at which information from the two ears is integrated.
Superior olivary nucleus
Definition
an extracellular connective tissue that covers the mechanically-sensitive hair bundles of the sensory receptor cells in the inner ear.
Tectorial membrane
Definition
a type of neural coding which relies on precise timing of action potentials or inter-spike intervals
Temporal coding
Definition
the character or quality of a musical sound or voice as distinct from its pitch and intensity.
Timbre
Definition
extracellular filaments that connect stereocilia to each other or to the kinocilium in the hair cells of the inner ear
Tip links
Definition
the arrangement of pitches and/or chords of a musical work in a hierarchy of perceived relations, stabilities, attractions and directionality
Tonality
Definition
perceptual experience of increasing pitch as tone’s frequency (wavelength increases)
Tone height
Definition
a membrane forming part of the organ of hearing, which vibrates in response to sound waves. In humans and other higher vertebrates it forms the eardrum, between the outer and middle ear.
Tympanic membrane
What are the two different definitions of sound?
- Physical definition: sound is created by pressure changes in the air or other medium
- Perceptual definition: sound is the experience we have when we hear
How do loud speakers produce sound?
- The diaphragm of the speaker moves out, pushing air molecules together called condensation.
- The diaphragm also moves in, pulling the air molecules apart called rarefaction.
- The cycle of this process creates alternating high- and low-pressure regions that travel through the air.
What is the term used to describe our perception of sound amplitude?
Loudness
What unit is loudness measured in?
Decibels (dB)
The higher the amplitude, the ________ the loudness
The higher the amplitude, the higher the loudness
What unit is frequency measured in?
Hertz (Hz)
What is the term used to describe our perception of frequency?
Pitch
What is tone height?
Tone height is the increase in pitch that happens when frequency is increased.
____________ is the repetition rate and is called the first harmonic
Fundamental frequency is the repetition rate and is called the first harmonic
___________ - process of adding harmonics to create complex sounds
____________ - display of harmonics of a complex sound
_____________ - buildup of sound at the beginning of a tone
___________ - decrease in sound at end of tone
__________ - basically a function of frequency; the perceived pitch of complex sound is determined by the fundamental frequency
Additive synthesis - process of adding harmonics to create complex sounds
Frequency spectrum - display of harmonics of a complex sound
Attack of tones - buildup of sound at the beginning of a tone
Decay of tones - decrease in sound at end of tone
Pitch - basically a function of frequency; the perceived pitch of complex sound is determined by the fundamental frequency
What does timbre reflect?
The number and magnitude of harmonics
Why do different musical instruments playing the same chord sound different?
Timbre - even though the fundamental frequency is the same, the higher order harmonics differ
What happens when you remove the first harmonic of a complex periodic sound?
Removal of the first harmonic results in a sound with the same perceived pitch, but with a different timbre.
>This is called a periodicity pitch
What is the range of human hearing?
20 to 20,000 Hz
What are the names of the boundaries of the auditory response area of the auditory curve?
Threshold of feeling
Threshold of hearing
What is being shown in this diagram?
(a) Movement of hair cilia in one direction opens ion channels in the hair cell, which results in the release of neurotransmitter onto an auditory nerve fiber; (b) Movement in the opposite direction closes the ion channels so there is no ion flow and no transmitter release.
What are the two ways nerves fibers signal frequency?
-
Which fibers are responding
- Specific groups of hair cells on basilar membrane activate a specific set of nerve fibers;
-
How fibers are firing
- Rate or pattern of firing of nerve impulses
What is Bekesys’ Place Theory of Hearing? How was it determined?
Frequency of sound is indicated by the place on the organ of Corti that has the highest firing rate.
Békésy determined this in two ways:
- Direct observation of the basilar membrane in cadavers.
- Building a model of the cochlea using the physical properties of the basilar membrane.
Which part of the cochlea receives low frequencies? Which receives high frequencies?
Base: High frequencies (~20,000 Hz)
Apex: Low frequencies (~20 Hz)
How does the base of the basilar membrane differ physically to the apex?
Base of the membrane (by stapes) is:
- Three to four times narrower than at the apex.
- 100 times stiffer than at the apex.
What is this diagram showing?
A perspective view showing the traveling wave motion of the basilar membrane. This picture shows what the membrane looks like when the vibration is “frozen,” with the wave about two thirds of the way down the membrane. (From Tonndorf, 1960). A tone causes different points of the membrane to move up and down (out of phase
Envelope of the traveling wave:
- Indicates ________
- Hair cells at this point are ______
- Position of the peak is a function of __________.
Envelope of the traveling wave:
- Indicates the point of maximum displacement of the basilar membrane
- Hair cells at this point are stimulated the most strongly leading to the nerve fibers firing the most strongly at this location.
- Position of the peak is a function of frequency.
What is this diagram showing?
The outer hair cells (a) elongate when cilia bend in one direction; (b) contract when the cilia bend in the other direction. This results in an amplifying effect on the motion of the basilar membrane – ‘mechanical frequency tuning’
What is this diagram showing?
How hair cell activation and auditory nerve fiber firing area synchronized with pressure changes of the stimulus. The auditory nerve fiber fires when the cilia are bent to the right. This occurs at the peak of the sine-wave change in pressure.
In which structures do auditory nerve fibers synapse?
Cochlear nucleus
Superior olivary nucleus
Inerior colliculus
Medial geniculate nucleus
Auditory receiving area (A1)
Hierarchical processing occurs in the cortex
- Neural signals travel through the ____, then _____, followed by the ______area.
- Simple sounds cause activation in the ______area.
- ______and _________areas are activated in response to more complex stimuli made up of many frequencies.
Hierarchical processing occurs in the cortex
- Neural signals travel through the core, then belt, followed by the parabelt area.
- Simple sounds cause activation in the core area.
- Belt and parabelt areas are activated in response to more complex stimuli made up of many frequencies.
What are the three main auditort areas?
Core area
Belt area
Parabelt area
Which of the three main auditory areas is the primary auditory receiving area (A1) located?
Core area
How are neurons arranges in A1?
Tonotopic maps are found in A1
- Neurons that respond better to low frequencies are on the left and those that respond best to high frequencies are on the right.
True or False:
People find locating sounds behind them the most difficult
True
True or False:
Location cues are not contained in the receptor cells like on the retina in vision
True
Processing of interaural disparity cues occurs in the _____________ - first site of binaural interaction
Processing of interaural disparity cues occurs in the superior olivary complex (SOC) - first site of binaural interaction
What is this diagram showing?
The principle behind interaural time difference (ITD). The tone directly in front of the listener, at A, reaches the left and the right ears at the same time. However, when the tone is off to the side, at B, it reaches the listener’s right before it reaches the left ear.
For what type of frequencies is an acoustic shadow relvant for? Why
Only relevant for high frequencies
The spaces between high-frequency sound waves is small compared to the head. The head interferes with the sound waves, creating an acoustic shadow on the other side of the head. Whereas, the spacing between low-frequency sound waves is large compared to the person’s head, so the sound is unaffected by the head.
What structure creates the acoustic shadow?
Head
Why are ILD and ITD not effective for judgments on elevation?
In many locations they may be equal (cone of confusion)
What two mechanisms have been proposed for source localisation?
Narrowly tuned ITD neurons
- They are found in the inferior colliculus and the superior olivary nuclei.
- This response is a form of specificity coding.
Broadly-tuned ITD neurons
- Research on gerbils indicates that neurons in the left hemisphere respond best to sound from the right, and vice versa.
- Location of sound is indicated by the ratio of responding for two types of neurons.
- This is a distributed coding system
What is this image describing?
How the Jeffress circuit operates. Axons transmit signals from the left ear (blue) and right ear (red) to neurons, indicated by circles. (a) Sound in front: signals start in left and right channels simultaneously. (b) Signals meet at neuron 5, causing it to fire. (c) Sound to the right: signal starts in the right channel first. (d) Signals meet at neuron 3, causing it to fire.
Identifying the sources of sound is largely a top-down/bottom-up process
Identifying the sources of sound is largely a top-down process
What heuristics help to perceptually organise sound stimuli?
Onset time
Location
Similarity of timbre and pitch
What does this image describe?
(a) When high and low tones are alternated slowly, auditory stream segregation does not occur, so the listener perceives alternating high and low tones. (b) Faster alternation results in segregation by grouping of pitch into high and low streams
