Ch. 9 Flashcards
amplitude (intensity)
in reference to sound, the magnitude of displacement (increase or decrease) of a pressure wave; perceived as loudness; magnitude of pressure change in a sound wave
frequency
in reference to sound, the number of times per second that a pattern of pressure change repeats; perceived as pitch
Hertz (Hz)
a unit of measure for frequency; 1 Hz = 1 cycle per second
loudness
the psychological aspect of sound related to perceived intensity (amplitude)
pitch
the psychological aspect of sound related to perceived frequency
- low frequency –> low pitch
- high frequency –> high pitch
decibel (dB)
a unit of measure for the physical intensity of sound; define the difference between two sounds as the ratio between two sound pressures
sine wave (pure tone)
the single waveform for which variation as a function of time is a sine function; a smooth, repeating wave shape that follows the pattern of a sine curve over time
all sounds can be described as…
combinations of sine waves
spectrum
a representation of the relative energy (intensity) present at each frequency
harmonic spectra
the spectrum of a complex sound in which various frequencies are at integer multiples of the fundamental frequency
fundamental frequency
the lowest-frequency component of a complex periodic sound; the first harmonic
timbre
the psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar
pinna
the outer, funnel-like part of the ear; sounds first collected from the environment by this
ear canal
the canal that conducts sound vibrations from the pinna to the tympanic membrane and prevents damage to the tympanic membrane
outer ear
the external sound-gathering portion of the ear, consisting of the pinna and the ear canal
tympanic membrane
the eardrum; a thin sheet of skin at the end of the outer ear canal; vibrates in response to sound; border between the outer ear and middle ear
ossicle
any of the three bones of the middle ear: malleus, incus, stapes
malleus
the most exterior of the three ossicles; receives vibration from the tympanic membrane and is attached to the incus
incus
the middle of the three ossicles, connecting the malleus and the stapes
stapes
the most interior of the three ossicles; connected to the incus on one end, presses against the oval window of the cochlea on the other end
oval window
the flexible opening to the cochlea through which the stapes transmits vibration to the fluid inside; border between the middle ear and inner ear
inner ear
a hollow cavity in the temporal bone of the skull, and the structures within this cavity: the cochlea and the semicircular canals of the vestibular system
ossicles are the smallest bones in the human body and they amplify sound vibrations in two ways
1) the joints between the bones are hinged in ways that make them work like levers: a modem amount of energy on one side of the fulcrum (joint) becomes larger on the other; this lever action increases the amount of pressure change by about a third
2) concentrate energy from a larger to a smaller surface area
middle ear has two muscles
tensor tympani and stapedius
tensor tympani
the muscle attached to the malleus; tensing this muscle decreases vibration
stapedius
attached to the stapes; tensing this muscle decreases vibration
purpose of the tensor tympani and stapedius
- to tense when sounds are very loud
- restrict movement of the ossicles and thus muffle pressure changes that might be large enough to damage the delicate structures in the inner ear
acoustic reflex
a reflex that protects the ear from intense sounds, via contraction of the stapedius and tensor tympani muscles
- also tensed during swallowing, talking, and general body movement, helping to keep the auditory system from being overwhelmed by sounds generated by our own bodies
cochlea
a spiral structure of the inner ear containing the organ of Corti
three parallel canals of the cochlea
tympanic canal, vestibular canal, middle canal
tympanic canal
one of the three fluid-filled passages in the cochlea; extends from the round window at the base of the cochlea to the helicotrema at the apex; filled with the fluid perilymph
vestibular canal
one of the three fluid-filled passages in the cochlea; extends from the oval window at the base of the cochlea to the helicotrema at the apex; filled with the fluid perilymph
middle canal
one of the three fluid-filled passages in the cochlea; sandwiched between the tympanic and vestibular canals and contains the cochlear partition; filled with the fluid endolymph
helicotrema
the opening that connects the tympanic and vestibular canals at the apex of the cochlea
stria vascularis
specialized tissue lines one side of the middle canal and maintains the right balance of charged ions in the endolymph to keep hair cells working at their best
three canals of the cochlea are separated by two membranes
Reissner’s membrane and basilar membrane
Reissner’s membrane
a thin sheath of tissue separating the vestibular and middle canals in the cochlea
basilar membrane
a plate of fibers that forms the base of the cochlear partition and separates the middle and tympanic canals in the cochlea
cochlear partition
the combined basilar membrane, tectorial membrane, and organ of Corti, which are together responsible for the transduction of sound waves into neural signals
traveling waves
movement of the oval window by vibrations transmitted through the tympanic membrane and middle-ear bones causes waves of pressure changes to flow through the fluid in the vestibular canal
round window
a soft area of tissue at the base of the tympanic canal that releases excess pressure remaining from extremely intense sounds
organ of Corti
a structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites and auditory nerve fibers
hair cell
any cell that has stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain; some also receive inputs from the brain
auditory nerve (AN)
a collection of neurons that convey information from hair cells in the cochlea to the brainstem (afferent neurons) and from the brainstem to the hair cells (efferent neurons)
stereocilium
any of hairlike extensions on the tips of hair cells in the cochlea that, when flexed, initiate the release of neurotransmitters
tectorial membrane
a gelatinous structure, attached on one end, that extends into the middle canal of the cochlea, floating above inner hair cells and touching outer hair cells; stimulates the hair cells
tip link
a tiny filament that stretches from the tip of a stereocilium to the side of its neighbor
mechanoelectrical transduction
when a stereocilium deflects, the tip link pulls on the taller stereocilium in a way that opens an ion pore for just a tiny fraction of a second –> permits potassium ions to flow rapidly into the hair cell, causing rapid depolarization –> depolarization leads to a rapid influx of calcium ions and initiation of the release of neurotransmitters from the base of the hair cell to stimulate dendrites of the auditory nerve
brief summary of the process of sound transmission
- air pressure wave is funneled by the pinna through the external ear canal to the tympanic membrane, which vibrates back and forth in time with the sound wave
- tympanic membrane vibrates the malleus, which vibrates the incus, which vibrates the stapes, which pushes and pulls on the oval window
- movement of the oval window causes pressure bulges to move down the length of the vestibular canal, and these bulges in the vestibular canal move the middle canal up and down
- this up-and-down motion forces the tectorial membrane to shear across the organ of Corti, moving the stereocilia atop hair cells back and forth
- pivoting of stereocilia initiates rapid depolarization that results in spurts of neurotransmitter released into synaptic clefts between the hair cells and dendrites of auditory nerve fibers
- these neurotransmitters initiate action potentials in the auditory nerve fibers and these signals are carried to the brain
depending on the frequencies of a sound…
the cochlear partition is displaced up and down in different places along the length of the cochlea
place code
tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition that has the greatest mechanical displacement
cochlear tuning to frequency caused by…
differences in the structure of the basilar membrane along the length of the cochlea
- higher frequencies affect the narrower, stiffer regions of the basilar membrane near the base more
- lower frequencies cause greater displacements in the wider, more flexible regions near the apex
afferent fiber
a neuron that carries sensory information to the central nervous system
efferent fiber
a neuron that carries information from the central nervous system to the periphery
threshold tuning curves
a graph plotting the thresholds of a neuron in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response
characteristic frequency (CF)
the frequency to which a particular auditory nerve fiber is most sensitive
electromotility
the ability of outer hair cells to extend and contract which changes the stiffness and sensitivity of the cochlear partition
otoacoustic emissions
activity of outer hair cells create these sounds
two-tone suppression
a decrease in the response (firing rate) of one auditory nerve fiber to one tone when a second tone is presented at the same time
isointensity curves
a map plotting the firing rate of an auditory nerve fiber against varying frequencies at varying intensities
rate saturation
the point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate
rate-intensity function
a graph plotting the firing rate of an auditory nerve fiber in response to a sound of constant frequency at increasing intensities
high-spontaneous fiber
an auditory nerve fiber that has a high rate (more than 30 spikes per second) of spontaneous firing; increase their firing rate in response to relatively low levels of sound
low-spontaneous fiber
an auditory nerve fiber that has a low rate (less than 10 spikes per second) of spontaneous firing; require relatively intense sound before they will fire at higher rates
mid-spontaneous fiber
an auditory nerve fiber that has a medium rate (10-30 spikes per second) of spontaneous firing; characteristics of these fibers are intermediate between those of low- and high-spontaneous fibers
the auditory system can accurately determine the frequency of incoming sound waves by…
integrating information across many AN fibers and using the pattern of firing rates across all these fibers
phase locking
firing of a single neuron at one distinct point in the period (cycle) of a sound wave at a given frequency
temporal code
tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to the period of the sound; reliable for lower frequencies
volley principle
the idea that multiple neurons can provide a temporal code for frequency is each neuron fires at a distinct point in the period of a sound wave but does not fire on every period
cochlear nucleus
the first brainstem nucleus at which afferent auditory nerve fibers synapse; there are two (right and left); contain several different types of specialized neurons
superior olive
an early brainstem region in the auditory pathway where inputs from both ears converge
inferior colliculus
a midbrain nucleus in the auditory pathway; neurons from the cochlear nucleus and superior olive travel up the brainstem to this structure
medial geniculate nucleus
the part of the thalamus that relays auditory signals to the temporal cortex an receives input from the auditory cortex
all structures of the auditory system show a consistent organizational pattern
neurons are aligned based on the frequencies to which they are most sensitive
- neurons most responsive to low-frequency energy lie on one edge of each structure
- neurons responding to high frequencies lie on the other edge
- neurons responding to other frequencies are spread out in an orderly fashion in between
tonotopic organization
an arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency
primary auditory cortex (A1)
the first area within the temporal lobes of the brain responsible for processing acoustic information
belt area
a region of cortex, directly adjacent to the primary auditory cortex (A1), with inputs form A1, where neurons respond to more complex characteristics of sounds
parabelt area
a region of cortex, lateral and adjacent to the belt area, where neurons respond to more complex characteristics of sounds, as well as to input from other senses
processing proceeds from simpler to more complex stimuli…
as we move farther along the auditory pathway
psychoacoustics
the branch of psychophysics that studies the psychological correlates of the physical dimensions of acoustics in order to understand how the auditory system operates
audibility threshold
the lowest sound pressure level that can be reliably detected at a given frequency
audibility threshold for human hearing
20-20,000 Hz
equal-loudness curve
a graph plotting sound pressure level (dB SPL) against the frequency for which a listener perceives constant loudness; starting point for each curve is always 1000 Hz
temporal integration
the process by which a sound at a constant level is perceived as being louder when it is of greater duration (longer)
masking
using a second sound, frequently noise, to make the detection of another sound more difficult
white noise
noise consisting of all audible frequencies in equal amounts
critical bandwidth
the range of frequencies conveyed within a channel in the auditory system
- smaller for low frequencies than for high frequencies
simplest way to introduce some hearing loss
obstruct the ear canal, thus inhibiting the ability of sound waves to exert pressure on the tympanic membrane
conductive hearing loss
hearing loss caused by problems with the bones of the middle ear; when the middle-ear bones lose (or are impaired in) their ability to freely convey (conduct) vibrations from the tympanic membrane to the oval window
otitis media
inflammation of the middle ear, commonly in children as a result of infection
- under these conditions, the oval window usually still vibrates, but without the amplifying power of the ossicles, hearing thresholds can be raised as much as 50 dB
otosclerosis
abnormal growth of the middle-ear bones that causes hearing loss
sensorineural hearing loss
hearing loss due to defects in the cochlea or auditory nerve
Three components to sensorineural hearing loss
1) “Sensory loss”
- Injury and loss of hair cells, mostly outer hair cells
- Auditory nerve responses are decreased and less selective for frequency
- With fewer inner hair cells, the neuronal firing pattern of the volley principle would become more difficult to maintain because there would be fewer neurons available to take turns firing
2) “Neural loss”
- actual loss of auditory nerve fibers
- aging
3) metabolic hearing loss
- hair cell activity decreases due to their surrounding fluid being compromised
metabolic hearing loss
hearing loss caused by degraded ability of the stria vascularis to provide sufficient nutrients and ions to the cochlear partition
major cause of sensorineural hearing loss
damage to hair cells by excessive exposure to noise
presbycusis
age-related hearing loss
electronic hearing aids
Use some means to amplify signals while also compressing intensity differences to keep the highest intensities within a comfortable listening level; Typically tuned to provide the greatest amplification only for frequencies in the region of greatest lost
hidden hearing loss
a type of hearing loss that cannot be easily detected by standard hearing tests; may explain some of the difficulties that human listeners have in noisy situations even when their audiograms are normal
