Topic 11: Hearing Flashcards
Sound
the perceptual experience of hearing
the statement “I hear a sound” is using sound in this sense
Sound Wave
pattern of pressure changes in a medium
most of the sounds we hear are due to pressure changes in the air, although sound can be transmitted through water and solids as well
Pure Tone
a tone with pressure changes that can be described by a single sine wave
Frequency
the number of times per second that pressure changes of a sound stimulus repeat
is measured in Hertz, where 1 Hertz is one cycle per second
Amplitude
in the case of a repeating sound wave, such as the sine wave of a pure tone, amplitude represents the pressure difference between atmospheric pressure and the maximum pressure of the wave
Hertz (Hz)
the unit for designating the frequency of a tone
1 Hertz equals one cycle per second
Decibel (dB)
a unit that indicates the pressure of a sound stimulus relative to a reference pressure: dB = 20log(p/po), where p is the pressure of the tone and po is the reference pressure
Sound Pressure Level
a designation used to indicate that the reference pressure used for calculating a tone’s decibel rating is set at 20 micropascals, near the threshold in the most sensitive frequency range for hearing
Level
short for sound pressure level or sound level
indicates the decibels or sound pressure of a sound stimulus
Sound Level
the pressure of a sound stimulus, expressed in decibels
Periodic Waveform
for the stimulus for hearing, a pattern of repeating pressure changes
Fundamental Frequency
the first harmonic of a complex tone
usually the lowest frequency in the frequency spectrum of a complex tone
the tone’s other components, called higher harmonics, have frequencies that are multiples of the fundamental frequency
Harmonic
pure-tone components of a complex tone that have frequencies that are multiples of the fundamental frequency
Fundamental
a pure tone with frequency equal to the fundamental frequency of a complex tone
Higher Harmonics
pure tones with frequencies that are whole number (2, 3, 4, etc.) multiples of the fundamental frequencies
Frequency Spectra
a plot that indicates the amplitudes of the various harmonics that make up a complex tone
each harmonic is indicated by a line that is positioned along the frequency axis, with the height of the line indicating the amplitude of the harmonic
Loudness
the quality of sound that ranges from soft to loud
for a tone of a particular frequency, loudness usually increases with increasing decibels
Audibility Curve
a curve that indicates the sound pressure level (SPL) at threshold for frequencies across the audible system
Auditory Response Area
the psychophysically measured area that defines the frequencies and sound pressure levels over which hearing frequencies and sound pressure levels over which hearing functions
this area extends between the audibility curve and the curve for the threshold of feeling
Equal Loudness Curves
a curve that indicates the sound pressure levels that result in a perception of the same loudness at frequencies across the audible spectrum
Pitch
the quality of sound, ranging from low to high, that is most closely associated with the frequency of a tone
Tone Height
the increase in pitch that occurs as frequency is increased
Tone Chroma
the perceptual similarity of notes separated by one or more octaves
Octave
tones that have frequencies that are binary multiples of each other (2, 4, etc.)
for example, an 800-Hz tone is one octave above a 400-Hz tone
Effect of the Missing Fundamental
removing the fundamental frequency and other lower harmonies from a musical tone do not change the tone’s pitch
Timbre
the quality that distinguishes between two tones that sound different even though they have the same loudness, pitch, and duration
differences in timbre are illustrated by the sounds make by different musical instruments
Attack
the buildup of sound energy that occurs at the beginning of a tone
Decay
the decrease in the sound signal that occurs at the end of a tone
Periodic Sounds
a sound stimulus in which the pattern of pressure changes repeats
Aperiodic Sounds
sound waves that do not repeat
Outer Ear
the pinna and the auditory canal
Pinnae
the part of the ear that is visible on the outside of the head
Auditory Canal
the canal through which air vibrations travel from the environment to the tympanic membrane
Tympanic Membrane
a membrane at the end of the auditory canal that vibrates in response to vibrations of the air and transmits these vibrations to the ossicles in the middle ear
Eardrum
another term for the tympanic membrane, the membrane located at the end of the auditory canal that vibrates in response to pressure changes
this vibration is transmitted to the bones of the middle ear
Resonance
a mechanism that enhances the intensity of certain frequencies because of the reflection of sound waves in a closed tube
resonance in the auditory canal enhances frequencies between about 2,000 and 5,000 Hz
Resonant Frequency
the frequency that is most strongly enhanced by resonance
the resonance frequency of a closed tube is determined by the length of the tube
Middle Ear
the small air-filled space between the auditory canal and the cochlea that contains the ossicles
Ossicles
three small bones in the middle ear that transmit vibrations from the outer to the inner ear
Malleus
the first of the ossicles of the middle ear
receives vibrations from the tympanic membrane and transmits these vibrations to the incus
Incus
the second of the ossicles of the middle ear
it transmits vibrations from the malleus to the stapes
Stapes
the last of the three ossicles of the middle ear
it receives vibrations from the incus and transmits these vibrations to the oval window of the inner ear
Oval Window
a small, membrane-covered hole in the cochlea that receives vibrations from the stapes
Middle Ear Muscles
muscles attached to the ossicles in the middle ear
the smallest skeletal muscles in the body, the contract in response to very intense sounds and dampen the vibration of the ossicles
Inner Ear
the innermost division of the ear, containing the cochlea and the receptors for hearing
Cochlea
the snail-shaped, liquid-filled structure that contains the structures of the inner ear, the most important of which are the basilar membrane, the tectorial membrane, and the hair cells
Cochlear Partition
a partition in the cochlea, extending almost its full length, that separates the scala tympani and the scala vestibuli
the organ of Corti, which contains the hair cells, is part of the cochlear partition
Organ of Corti
the major structure of the cochlear partition, containing the basilar membrane, the tectorial membrane, and the receptors for hearing
Hair Cells
neurons in the cochlea that contain small hairs, or cilia, that are displaced by vibration of the basilar membrane and fluids inside the inner ear
there are two kinds of hair cells, inner and outer
Basilar Membrane
a membrane that stretches the length of the cochlea and controls the vibration of the cochlear partition
Tectorial Membrane
a membrane that stretches the length of the cochlea and is located directly over the hair cells
vibrations of the cochlear partition cause the tectorial membrane to bend the hair cells by rubbing against them
Stereocilia
thin processes that protrude from the tops of the hair cells in the cochlea that bend in response to pressure changes
Tip Links
structures at the tops of the cilia of auditory hair cells, which stretch or slacken as the cilia move, causing ion channels to open or close
Phase Locking
firing of auditory nerves in synchrony with the phase of an auditory stimulus
Traveling Wave
in the auditory system, vibration of the basilar membrane in which the peak of the vibration travels from the base of the membrane to its apex
Apex
the end of the cochlea farthest from the middle ear
Base
the end of the cochlea nearest the middle ear
Tonotopic Map
an ordered map of frequencies created by the responding of neurons within structures in the auditory system
there is a tonotopic map of neurons along the length of the cochlea, with neurons at the apex responding best to low frequencies and neurons at the base responding best to high frequencies
Frequency Tuning Curve
curve relating frequency and the threshold intensity for activating an auditory neuron
Characteristic Frequency
the frequency at which a neuron in the auditory system has its lowest threshold
Cochlear Amplifier
expansion and contraction of the outer hair cells in response to sound sharpens the movement of the basilar membrane to specific frequencies
this amplifying affect plays an important role in determining the frequency selectivity of auditory nerve fibers
Place Theory
the proposal that the frequency of a sound is indicated by the place along the organ of Corti at which nerve firing is highest
modern place theory is based on Bekesy’s traveling wave theory of hearing
Resolved Harmonics
harmonics in a complex tone that create separated peaks in basilar membrane vibration, and so can be distinguished from one another
usually lower harmonics of a complex tone
Unresolves Harmonics
harmonics of a complex tone that can’t be distinguished from one another because they are not indicated by separate peaks in the basilar membrane vibration
the higher harmonics of a tone are most likely to be unresolved
Amplitude-Modulated Noise
a noise sound stimulus that is amplitude modulated
Amplitude Modulation
adjusting the level (or intensity) of sound stimulus so it fluctuates up and down
Temporal Coding
the connection between the frequency of a sound stimulus and the timing of the auditory nerve giber firing
Subcortical Structures
structure below the cerebral cortex
for example, the superior colliculus is a subcortical structure in the visual system
the cochlear nucleus and superior olivary nucleus are among the subcortical structures in the auditory system
Cochlear Nucleus
the nucleus where nerve fibers from the cochlea first synapse
Superior Olivary Nucleus
a nucleus along the auditory pathway from the cochlea to the auditory cortex
the superior olivary nucleus receives inputs from the cochlear nucleus
Inferior Colliculus
a nucleus in the hearing system along the pathway from the cochlea to the auditory cortex
the inferior colliculus receives inputs from the superior olivary nucleus
Medial Geniculate Nucleus
an auditory nucleus in the thalamus that is part of the pathway from the cochlea to the auditory cortex
the medial geniculate nucleus receives input from the inferior colliculus and transmits signals to auditory cortex
Primary Auditory Cortex
an area of the temporal lobe that receives signals via nerve fibers from the medial geniculate nucleus in the thalamus
Pitch Neurons
a neuron that responds to stimuli associated with a specific pitch
these neurons fire to the pitch of a complex tone even if the first harmonic or other harmonies of the tone are not present
Presbycusis
a form of sensorineural hearing loss that occurs as a function of age and is usually associated with a decrease in the ability to hear high frequencies
since this loss also appears to be related to exposure to environmental sounds, it is also called sociocusis
Noise-Induced Hearing Loss
a form of sensorineural hearing loss that occurs when loud noises cause degeneration of the hair cells
Leisure Noise
noise associated with leisure activities such as listening to music, hunting, and woodworking
exposure to high levels of leisure noise for extended period can cause hearing loss
Hidden Hearing Loss
hearing loss that occurs at high sound levels, even though the person’s thresholds, as indicated by the audiogram, are normal
Audiogram
plot of hearing loss versus frequency
What is sound?
pressure waves in the air produced by a vibrating object, which are detected by the auditory system
What is the distal stimulus for sound?
vibrating object
What is the proximal stimulus for sound?
pattern of kinetic energy at the eardrum
What is the phase of sound?
point along the wave, measured in degrees
has no direct perceptual counterpart
What is the amplitude of sound?
displacement of wave from peak to trough
What is the frequency of sound?
number of sound wave cycles per second
What are the physical aspects of sound?
phase, amplitude, frequency
What is the loudness of sound?
perceptual experience of sound intensity (not “volume”)
associated with amplitude and sound pressure
to measure loudness, compare to a standard sound
to double loudness, increase dB by ~10 dB (e.g., 60 dB is twice as loud as 50 dB)
What is the pitch of sound?
quality of a sound ranging from low to high; allows sounds to be ordered on a musical scale
most closely associated with frequency: ranges from 20-20000 Hz
also affected by intensity: high frequency sounds seem higher pitched as intensity increases, low frequency sounds seem lower pitched as intensity increases
duration effects: sound < 10 ms long is heard as a “click”
What is the chromatic scale of musical notes?
one note is an octave above another when its frequency is double that of the comparison
octave subdivided into 12 intervals (or semitones), equally spaced logarithmically
tones in this scale match harmonic ratios found in the sound of human vocalization, specifically in English vowel sounds
other scales use different ratios to establish a scale (a.k.a. “microtonal” or “microtuned”)
What is a fundamental?
lowest frequency in a Fourier spectrum of a complex sound wave
What are harmonics?
components of a complex sound having frequencies that are multiples of the fundamental
the number and amplitude of harmonics contribute to the timbre of a sound
What is timbre?
“character” or “nature” of a sound
makes a violin sound different from a piano
due to the different frequency components (fundamental + harmonics) produced by vibrating source stimulus
What was the Sivian & White (1933) view of the auditory threshold?
each frequency has a different threshold
audibility curve: describes absolute threshold for hearing each different frequency
auditory response area: the dynamic range of intensities from threshold to pain
What was the Fletcher & Munson (1933) view of the auditory threshold?
equal loudness curve: graph of decibel levels of various frequencies that seem equally loud
How is the equal loudness curve determined?
present standard: 1000 Hz tone at a certain dB level
adjust intensity of other frequencies to match loudness of standard
What factors affect the auditory threshold?
auditory adaptation: same sound seems softer if presented for a long time
auditory fatigue: temporary hearing loss due to high-intensity sounds, typically frequencies at and above the sound are lost
What is the pinna?
the “ear” on the side of your head
channels certain sound waves
What is the external auditory meatus (ear canal)?
protects middle and inner ears
amplifies frequencies 2000 to 5000 Hz via resonance: sound waves near the resonant frequency of the ear canal are reflected from the closed end of the canal, reinforcing incoming sound waves of the same frequency (like blowing across the top of a bottle)
What is the tympanic membrane (eardrum)?
struck by sound waves and vibrates
transmits sound to structures in middle ear
What are the ossicles?
malleus (hammer), incus (anvil), stapes (stirrup); supported by middle-ear muscles
malleus connected to eardrum; stapes to oval window
What is the function of the ossicles?
concentrate vibration of eardrum (0.6 cm2) to oval window (0.032 cm2); increases pressure by ~20:1 ratio
acts as levers, increasing vibration by a factor of 1.3x
Why is the increased pressure provided by the ossicles needed?
outer and middle ear filled with air; inner ear with cochlear fluid
transmitting wave into denser medium: loss of pressure
ossicles help compensate for this loss
What is the Eustachian tube?
equalizes middle ear pressure with outside
What are the semicircular canals?
involved in 3-D balance
vestibular sense
What is the cochlea?
snail-shaped structure, filled with cochlear fluid; has 2 3/4 turns; is divided in canals
scala vestibuli (vestibular canal)
scala tympani (tympanic canal) (connected by helicotrema at apex end)
scala media (cochlear partition): formed by basilar membrane and Reissner’s membrane
What is the Organ of Corti?
tectorial membrane overhangs basilar membrane, which contains 15,000 hair cells
What are the characteristics of inner hair cells?
number: 3,000
cell alignment: 1 row
cilia number: 40-60/cell
cilia alignment: straight lines
function: sensory
What are the characteristics of outer hair cells?
number: 12,000
cell alignment: 3-5 rows
cilia number: 100-120/cell
cilia alignment: V- or W-shaped rows
function: supportive
What are spiral ganglion cells?
30,000 nerve fibres
95% are type I: 3-15 fibres/inner hair cells; large, myelinated
5% are type II: 1 fibre/10 outer hair cells; small, slow
What is the path of transduction of sound in the ear?
vibration –> eardrum –> ossicles –> oval window –> vestibular canal/cochlear partition (cochlear fluid) –> basilar membrane
basilar and tectorial membranes move laterally with respect to each other
shearing force bends cilia of outer hair cells, which are embedded in tectorial membrane
cilia of inner hair cells bent by fluid flow: actin fibres link tips of cilia, when the cilia bend actin stretches and opens a “trap door”, this allows K+ ions into the hair cell which initiates the neural signal by releasing glutamate
What are the auditory pathways?
axons of spiral ganglions comprise auditory nerve
superior olives send efferent fibres (feedback) to the outer hair cells
What is tonotopic organization?
neurons activated by similar frequencies are found close to each other
this organization is preserved from basilar membrane to auditory cortex
40% of neurons respond to noise, clicks, bangs
60% of neurons respond to a certain frequency
Why do 60% of neurons respond to a certain frequency?
complex sounds can be decomposed by Fourier analysis into component sine waves (pure tone)
this appears to be done by the auditory system
thus, we don’t need one neuron to respond to middle C on a violin, another for middle C on a piano, etc.
but some neurons are responsive to specific stimuli: squirrel monkeys have squirrel-monkey-sound-detectors
What is place code?
the activity of specific neurons encodes different frequencies
What is resonance theory?
basilar membrane appeared to be composed of transverse fibres
sound makes fibre vibrate like a harp-string
each fibre activated by a certain frequency
problem: basilar membrane is all connected; no independent stringlike fibres
What is traveling wave theory?
traveling wave: entire membrane vibrates
basilar membranes varies in elasticity down its length: narrow/stiff at oval window (base), wide/floppy at helicotrema (apex)
each frequency has its own point of maximum displacement along the membrane: high frequencies activate hair cells at base, low frequencies activate hair cells at apex
What is the observational evidence for traveling wave theory?
seeing shape of traveling wave on basilar membrane
matched predictions
What is the evidence for traveling wave theory using the frequency tuning curve?
many auditory neurons display frequency tuning curve: responsive to a narrow range of frequencies
point of greatest sensitivity: characteristic frequency
partly due to selective connections from certain hair cells along the basilar membrane
What is the evidence for traveling wave theory using tonotopic organization?
nerve fibres coming from base tuned to high frequencies
those from apex tuned low frequencies
What is the evidence for traveling wave theory using stimulation deafness experiments?
high intensity sounds damage part of the organ of Corti
high frequencies: damage near oval window (base)
low frequencies: damage near helicotrema (apex)
What is the evidence for traveling wave theory using motile response?
subsequent research showed pattern of vibration on basilar membrane is narrower than von Bekesy found
active process sharpens wave
cochlear amplifier: outer hair cells sharpen wave around the peak by tilting and changing length
two-tone suppression: present tone at characteristic frequency of a neuron, turn on another tone, close in frequency to the other, neuron’s response rate decreases, due to outer hair cells affecting movement of basilar membrane
What is the evidence for traveling wave theory using masking experiments?
one sound (masker) prevents us from hearing another (target)
masking increases as masker and target frequencies become closer
masking is asymmetrical: target frequencies higher than masker are more affected than frequencies lower than masker
due to location of vibration on the basilar membrane
to reduce file size, frequencies that would have been masked anyway are removed in the encoding of digital audio files (e.g., MP3 files) a process called perceptual coding
How is the case of the missing fundamental a problem for place coding?
region on basilar membrane is not moving, so how is pitch corresponding to that location heard?
present harmonics in one ear; other harmonics to other ear; missing fundamental will be perceived
this illusion must be determined by a CNS structure that integrates binaural information
Getty & Howard (1981): central pitch processor analyzes the pattern of harmonics and selects the most likely fundamental frequency that would be part of the pattern
What is temporal code?
the timing of neural activity encode different frequencies
What is frequency theory?
entire basilar membrane vibrates in synch with frequency
assumed that each vibration produced one action potential in all receptors
What are the problems with frequency theory?
actually, only part of the membrane moves
refractory period of neurons - cells need time to recover before firing again: max frequency is 1,000/second
What is the Volley principle?
groups of neurons fire alternately in volleys – some fire while others are refractory
phase locking: neuron firing is synchronized with the peak of a pure tone stimulus
frequency coded by which neurons are firing, and how much
doesn’t work well at high frequencies; phase locking works best for low frequencies (below 5000 Hz)
Is place coding or temporal coding the correct approach?
there is evidence for both coding approaches; they work in combination
What is tinnitus?
definition: hearing ringing in the ears, or experiencing a sound when none is present
affects 13 million North Americans, including over 2.4 million Canadians
third worst thing that can happen to you (below only intractable severe pain, and intractable severe dizziness)
can cause difficulty concentrating; anxiety and depression
most commonly caused by loud sounds, but also certain drugs, ear infections, or food allergies
early theories implicated emissions/acoustic echoes in the ear
What are the implied central mechanisms of tinnitus?
patients who had cancerous auditory nerve removed developed ringing
MRIs of patients with ringing in only one ear showed area in inferior colliculus affected
some deaf people can modulate intensity and pitch of the ringing by moving their eyes left or right
What are the current theories regarding tinnitus?
- destroying hair cells causes the brain to remap areas previously served by the destroyed hair cells, resulting in abnormal brain activity
- due to decreased incoming stimulation, there is less inhibition in the auditory cortex, resulting in more excitatory activity and phantom sound
What is presbycusis?
age-related hearing loss, due to degeneration of hair cells and cilia
more likely to occur with increasing age
higher frequencies are more attenuated with age
presbycusis causes include: heredity, vascular diseases, ototoxic drugs, and exposure to loud noise
younger people are increasingly experiencing NIHL: 30% listen to levels of at least 91 dB for an average of 2.9 hours/day
What are the warning signs of noise exposure/hearing loss?
ringing/buzzing in the ears
muffled sounds
difficulty understanding speech
difficulty following conversations over background noise
having to turn up the TV to hear it clearly
What are the ways one can prevent noise-induced hearing loss?
turn down/avoid high intensity sounds
iPod and iPhone capable of up to 115 dB
most vulnerable occupations: musicians, bartenders/servers. mechanics, construction workers, dentists and assistants
wear earplugs
