Chapter 9 Sound and the Ears Pg 287 Flashcards
Sound waves
Waves of pressure changes in air caused by the vibrations of a source
Cycle
Repeating segment of air pressure changes
*in a sound wave
Inverse square law
Falloff in sound energy with distance
*Energy of sound decreases in proportion to the square of the distance from the source
Three physical dimensions and perceptual dimensions
- Frequency=pitch
- Amplitude=loudness
- Waveform=timbre (sound quality)
Periodic sound waves
waves in which the cycles of compression and rarefaction repeat in a regular, or periodic fashion- opposed to aperiodic sound waves
Pure tone
Sound wave in which air pressure changes over time according to a mathematical formula called a sine wave, or sinusoid
Frequency
*Physical dimension of sound that is related to the perceptual dimension of pitch; expressed in hertz, the number of cycles per second of a periodic sound wave
Pitch
Perceptual dimension of sound that corresponds to the physical dimension of frequency; the perceived highness/lowness of sound
Hertz (Hz)
number of cycles per second of sound wave; the physical unit used to measure frequency
*Unimpaired hearing young adults- 20 to 20,000 Hz
Amplitude
The difference between the maximum and minimum sound pressure in a sound wave; the physical dimension of sound that is related to the perceptual dimension of loudness
Loudness
perceptual dimension of sound that is related to the physical dimension of amplitude; how intense/quiet a sound seems
*Peak amplitude: largest peak-to-trough difference
Decibels (dB)
Physical unit used to measure sound amplitude; logarithmically related to sound pressure measured in micropascals
- dB SPL= 20 log (p/p0)
- p is the measured sound pressure in micropascals (uPa)
- p0 is an internationally agreed-upon reference sound pressure of 20 uPa
- Just noticeable difference in intensity of sound= 1dB
- Physical sound pressure of less than 20 uPa are inaudible
Audibility curve
a curve showing the minimum amplitude at which sounds can be detected at each frequency
- The audibility threshold at the lower and higher frequencies that people can hear is much greater than it is at frequencies near the middle, around 500-5,000 Hz
- Auditory sensitivity is maximal in this middle range which happens to be the range of frequencies present in most human speech sounds
Equal loudness contour
A curve showing the amplitude of tones at different frequencies that sound about equally loud
*Our hearing is best for frequencies between 500-5,000 Hz
Unit of loudness
Phon
*Numerically equal to the amplitude of a 1,000 Hz tone- a 1,000 Hz tone at 10dB SPL has a loudness of 10 phons
Fourier analysis
mathematical procedure for decomposing a complex waveform into a collection of sine waves with various frequencies and amplitudes
Fourier spectrum
depiction of the amplitudes at all frequencies that make up a complex waveform
*Full array of its component frequencies with their specific amplitudes
Fundamental frequency
frequency of the lowest-frequency component of a complex waveform; determines the perceived pitch of the sound
Harmonic
component frequency of a complex waveform that is an integer multiple of the fundamental frequency; the first harmonic is the fundamental frequency; the second harmonic is twice the fundamental frequency, and so on.
Overtones
second and higher harmonics
- Second and higher harmonics are integer multiples of the fundamental frequency in many periodic sounds
- Complex periodic sounds’ qualify of their sound depends on the frequency and amplitude of their fundamental frequency and of each overtone
Timbre
difference in sound quality between two sounds with the same pitch and loudness; for complex periodic sounds, timbre is mainly due to differences in the relative amplitudes of the sounds’ overtones; the perceptual dimension of sound that is related to the physical dimension of waveform
- Low amplitude overtones contribute less to timbre
- Such differences in the relative amplitudes of harmonics are what give each sound its distinctive timbre
Pinna
outermost portion of ear; like a funnel and consists of fat and cartilage with various random-looking folds and ridges in it
*Modify the incoming sound in a way that contributes to sound localization
Auditory canal
narrow channel that funnels sound waves gathered by the pinna onto the tympanic membrane and that amplifies certain frequencies in those waves
*Amplifies frequencies in the range of 2,000-5,000 Hz, which contributes to the high sensitivity to those frequencies
Tympanic membrane
eardrum
*thin, elastic diaphragm at the inner end of the auditory canal that vibrates in response to the sound waves that strike it; it forms an airtight seal between the outer ear and the middle ear
Ossicles
three smallest bones in human body
*Malleus, incus, stapes in middle ear
Malleus, incus, stapes
Transmit sound energy from the tympanic membrane to the inner ear
*tympanic membrane pushes on malleus -> incus -> displaces the stapes -> oval window
Oval window
membrane-covered opening at the base of the cochlea; vibrations of the membrane transmit sound energy from the ossicles into the cochlea
Cochlea with fluid leads to 30-dB loss of sound energy
Heavy traffic of sound; cannot hear a lot of quiet sounds
2 Characteristics of ear anatomy help compensate for this loss of sound energy
- Tympanic membrane is about 15-20 times larger in area than the oval window= all the sound energy collected by the tympanic membrane is concentrated on a much smaller area, effectively amplifying its effect there
- Physical arrangement of the ossicles produces a sort of lever action with the result that a relatively small movement of the malleus ends up by causing a relative large displacement of the stapes- thus, the action of the ossicles magnifies the vibrations of the tympanic membrane, just as a small movement of one end of a lever can cause a much larger movement of the other end.
Acoustic reflex
reflexive contraction of two tiny muscles in the middle ear in response to high-intensity sounds; it dampens the movement of the ossicles, which helps protect the auditory system from damage due to loud noises
- Limited capacity to prevent damage
- Occurs mainly in response to lower frequencies
- Vulnerable to damage from exposure to loud high-frequency noises
- Takes more than one-tenth of a second to occur, making it too slow to protect the auditory system from sudden, brief high-intensity sounds
- Reduce interference produced by our own speech sounds and by other self-produced noises such as coughing and chewing
Eustachian tube
tube connecting the middle ear and top part of the throat; normally closed but can be briefly opened to equalize the air pressure in the middle ear with the air pressure outside
Cochlea
coiled, tapered tube within the temporal bone of the head, partitioned along its length into three chambers; contains the structures involved in auditory transduction
Vestibular canal
one of the 3 chambers in the cochlea; separated from the cochlear duct by Reissner’s membrane; filled with perilymph
Cochlear duct
one of the 3 chambers in the cochlea; spearated from tympanic canal by basilar membrane; contains the organ of Corti; filled with endolymph
Tympanic canal
one of the 3 chambers in the cochlea; separated from the cochlear duct by the basilar membrane; filled with perilymph
Helicotrema
An opening in the partitioning membranes at the apex of the cochlea; provides an open pathway for the perilymph to carry vibrations through the cochlea
*2 canals connected
Round window
A membrane-covered opening at the base of the tympanic canal in the cochlea; serves as a kind of “relief valve” for the pressure waves traveling through perilymph
Basilar membrane
tapered membrane suspended between the walls of the cochlea; thicker, narrower, and stiffer at the base than at the apex
- The thickness, width, and stiffness change gradually and continuously from one end to the other
- The stiffness of the membrane at each location along its length that is the main determinant of how much the membrane moves at that location in response to different frequencies
- The stiff base of the membrane responds most readily to high frequencies, and the floppy apex responds most readily to low frequencies, with a gradual, continuous change in response from base to apex
- Separates out the frequencies of the sinusoidal components of complex wave, performing what amounts to a Fourier analysis of original sound wave
Characteristic frequency
frequency to which each location on the basilar membrane responds most readily
Organ of Corti
structure in the cochlea situated on the basilar membrane; consists of 3 critical components-inner hair cells, outer hair cells, and tectorial membrane
Inner hair cells
neurons responsible for auditory transduction
- One row of about 3,500 inner hair cells
- More pear shaped
- Tips of inner hair cell stereocilia are attached to tectorial membrane
- Connect to Type I auditory nerve fibers -> one/two inner hair cells -> multiple fibers
Outer hair cells
neurons serve to amplify and sharpen the responses of inner hair cells
- Cylindrical
- Tips of outer hair cell stereocilia are attached to tectorial membrane
- Connect to Type II auditory nerve fibers
Tectorial membrane
Membrane that lies above the hair cells in organ of Corti
Sterocilia
Small hairlike projections on the tops of inner and outter hair cells
- When the basilar membrane moves upward, the stereocilia at the tips of outer hair cells are bent by a shearing force due to the different motions of the two membranes
- The stereocilia of the inner hair cells are bent in the same direction by the resistance of the surrounding endolymph as the stereocilia move through the fluid
Auditory nerve
nerve that conveys signals from hair cells in the organ of Corti to brain; made up of Type I and Type II auditory nerve fibers bundled together
- 95% of Type I, 5% of Type II
- Type I: thick and myelinated -> promotes rapid conduction of action potentials
- Type II: thinner and unmyelinated -> relatively slower conduction of action potentials; respond only to very intense sounds-> detection of potentially damaging sounds
Tip links
tiny fibers connecting the tips of adjacent stereocilia on hair cells
*When stereocilia bend-> distance between attachment points of tip increase -> increase tension of tip links -> open ion channels -> positive charged potassium and calcium ions enter -> depolarize
Motile response
- Outer hair cells-> depolarization-> in a change in the shape of protein-prestin in membrane-> motile response
- Cell body and its stereocilia to execute physical movements similar to stretching and contracting
- Cell’s length changes by 2-3%
Response of outer hair cells’ effects on signals sent by inner hair cells
- Changes in length of outer hair cells magnify the movements of the basilar membrane in regions with characteristic frequencies corresponding to frequencies in sound
- Inner hair cells send stronger signals in response to the sound, motile response amplifies sounds
- Inner hair cells in those regions send signals that are more frequency specific- thus, the motile response sharpens the response to frequencies in sounds
Place code
frequency is represented by displacement of basilar membrane at different locations, with different degrees of displacement resulting in correspondingly different rates of action potentials being sent along the Type I auditory nerve fibers at those locations
- Nerve fibers with higher characteristic frequencies are more sensitive to frequency differences between incoming sounds near their characteristic frequency than are nerve fibers with lower characteristic frequencies. Thus, the place code provides relatively better frequency representation of high frequency sounds than of low-frequency sounds
- German scientist Hermann von Helmholz: different locations along the basilar membrane respond selectively to different frequencies of sound
Temporal code
frequency is represented by a match between the frequencies in the incoming sound waves and the timing of action potentials sent by Type I auditory nerve fibers to the brain
＊Based on a match between the frequencies in incoming sound waves and the firing rates of Type I auditory nerve fibers
*Time-locking mechanism:as long as action potentials are produced at the same time as the peaks in the incoming sound wave, even if not at every peak
*Temporal code with phase locking, can precisely represent frequencies up to about 5,000 Hz, while the place code provides the sharpest representations for frequencies above about 5,000 Hz
Dynamic range
Range of amplitudes that can be heard and discriminated; when applied to an individual auditory nerve fiber, the range of amplitudes over which the firing rate of the fiber changes
- as much greater than the firing rates of any one auditory nerve fiber
- The increase in the number of nerve fibers responding to a given tone as the tone’s amplitude increases is based on the fact that an individual nerve fiber doesn’t respond just to tones with the fiber’s characteristic frequency; rather, each fiber responds to a range of frequencies
- The number of possible of different fibers firing at different rates is enormous, and this enables the auditory system to discriminate very small differences in amplitude
- Fibers can differ in how they respond to tones that match their characteristic frequency
- The range of amplitudes over which the nerve fiber’s firing rate increases from baseline to saturation
- Different auditory nerve fibers have different thresholds and different dynamic ranges
- Auditory system can use the patterns of response of nerve fibers with different characteristic frequencies to gauge the amplitude of an incoming sound
Hearing impairment
decrease in a person’s ability to detect or discriminate sounds, compared to the ability of a healthy young adult
Tinnitus
Persistent perception of sound, such as a ringing or buzzing, not caused by any actual sound
- Range from a barely perceptible hiss/ringing to an intense roar
- Perceived in one/both ears
- intermittent/continuous
- Damage to the cochlea, irritation of or pressure on the auditotry nerve by a blood vessel or a tumor, and changes in neural circuits within the auditory cortex
- Noise- induced hearing loss
Audiometer
Instrument that presents pure tones with known frequency and amplitude to the right or left ear; used in estimating the listener’s absolute threshold for specific frequencies and to construct an audiogram
*Uses the staircase method to estimate the person’s absolute threshold for each of six to eight frequencies, ranging from 250-8,000 Hz
Audiogram
Graphical depiction of auditory sensitivity to specific frequencies, compared to the sensitivity of a standard listener; used to characterize possible hearing loss
Conductive hearing impairments
Loss of sound conduction to the cochlea, as a result of problems in the outer or middle ear, including a blockage of auditory canal, a perforated/torn tympanic membrane, damage to the ossicles
- Caused by otosclerosis, growth of bone in middle ear that interferes with the movement of ossicles
- Remove stapes and replace with artificial prosthetic stapes
- Otitis media/ earache: inflammation of middle ear
- Not profound
- With hearing aid
Sensorineural hearing impairment
hearing impairments caused by damage to the cochlea, the auditory nerve, or the auditory areas or pathways of the brain
- Congenital/acquired and can range from minor deficits in hearing some sound frequencies to profound, nearly total deafness
- Effect on spoken language
- Recessive gene inherited from both parents
- Early intervention prevent delayed language acquisition
- Acquired sensorineural hearing impairments= aging and effects of exposure to loud noise
Age related hearing impairment
Environmental factors
Genetic factors: hearing loss from age 20-80 increasing for men than women
Noise-induced hearing impairments
Prolonged exposure to sounds with an amplitude greater than about 85 dB SPL is likely to cause noise-induced hearing loss
- Temporary and revisible/permanent, depending on the noise level and its duration
- Noise-induced hearing loss is often maximal at 4,000 Hz and less severe at 8,000 Hz, leading to a V-shaped audiogram
- Different from pattern in age-related hearing loss -> progressively more severe as frequency increases
- Mechanical damage due to very high amplitude, pressure waves pulsing through the cochlea
- Hair cell death
