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Chapter 10

PSYC 320 Chapter 10: Chapter 10 Sound and the ears
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Department
Psychology
Course
PSYC 320
Professor
Brian Anderson
Semester
Spring

Description
1 Chapter 10: Sound and the ears Vocabulary • Sound waves-Waves of pressure changes in air caused by the vibrations of a source • Cycle- In a sound wave, a repeating segment of air pressure changes • Periodic sound waves- Waves in which the cycles of compression and refraction repeat in a regular, or periodic, fashion • Pure tone- A sound wave in which air pressure changes over time according to a mathematical formula called sine wave or sinusoid • Frequency- The 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- The perceptual dimension of sound that corresponds to the physical dimension of frequency; the perceived highness or lowness of a sound • Hertz (Hz)- The number of cycles per second of a wave, physical unit to measure frequency • 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- The perceptual dimension of sound that is related to the physical dimension of amplitude; how intense or quiet a sound seems • Decibels (dB)- A physical unit to measure sound amplitude; logarithmically related to sound pressure measured in micropascals • Audibility curve- A curve showing the minimum amplitude at which sounds can be detected at each frequency • Equal loudness contour- A curve showing the amplitude of tone at different frequencies that sound about equally loud • Phon- a unit of loudness; the loudness of a tone in phons is numerically equal to the amplitude of a 1,000 Hz tone that sounds equally loud • Fourier analysis- A mathematical procedure for decomposing a complex waveform into a collection of sine waves with various frequencies and amplitudes • Fourier spectrum-A depiction of the amplitudes at all frequencies that make up a complex wave form • Fundamental frequency- The frequency of the lowest-frequency component of a complex waveform; determines the perceived pitch of the sound • Harmonic- A component frequency of a complex waveform that is an integer multiple of the fundamental frequency; the second harmonic is twice the fundamental frequency and so on • Timbre- The 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 • Pinna- The outermost portion of the ear • Auditory canal- A narrow channel that funnels sound waves gathered by the pinna onto the tympanic membrane and that amplifies certain frequencies in those waves 1 2 • Tympanic membrane (eardrum)- A thin elastic diaphragm at the inner end of the auditory canal that vibrates in response to the sound waves that strike it; forms an airtight seal between the outer ear and the middle ear • Ossicles- 3 small bones (malleus, incus, stapes) in the middle ear that transmit sound energy from the tympanic membrane to the inner ear • Malleus (Hammer)- A small bone in the inner ear, transmits sound energy from tympanic membrane to the incus • Incus (Anvil)- A small bone in the inner ear, transmits sound energy from the malleus to the stapes • Stapes (stirrup)- A small bone in the inner ear; transmits sound energy from the incus to the oval window • Oval window- A membrane covered opening at the base of the cochlea; vibrations of the membrane transmit sound energy from the ossicles into the cochlea • Eustachian tube- A tube connecting the middle ear and the top part of the throat; normally closed but can be briefly opened (by swallowing or yawning) to equalize the pressure in the middle ear with the air pressure outside • Cochlea- A coiled, tapered tube within the temporal bone of the head, partitioned along its length into 3 chambers; contains the structures involves in auditory transduction • Vestibular canal- One of the 3 chambers; separated from the cochlear duct by Reissner’s membrane; filled with perilymph • Cochlear duct- One of the 3 chambers; separated from the tympanic canal by the basilar membrane; contains the organ of Corti; filled with endolymph • Tympanic canal- One of the 3 chambers; 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 • Round window- A membrane covered opening at the base of the tympanic canal in the cochlea; serves as a “relief valve” for the pressure waves traveling through the perilymph • Basilar membrane- A tapered membrane suspended between the walls of the cochlea; thicker, narrower, and stiffer at the base than at the apex • Characteristic frequency- The frequency to which each location on the basilar membrane responds most readily • Organ of Corti- A structure in the cochlea situated on the basilar membrane; consists of 3 critical components- inner hair cells, outer hair cells, and the tectorial membrane • Inner hair cells- Neurons in the organ of Corti; Responsible for auditory transduction • Outer hair cells- Neurons in the organ of Corti; serve to amplify and sharpen the responses of inner hair cells • Tectorial membrane- A membrane that lies above the hair cells in the organ of Corti • Stereocilia- Small hair-like projections on the tops of inner and outer hair cells 2 3 • Auditory nerve- The nerve that conveys signals from the hair cells in the organ of Corti to the brain; made up of Type 1 and Type 2 auditory nerve fibers bundled together • Tip links- Tiny fibers connecting the tips of adjacent stereocilia on hair cells; increased tension on tip links pulls open ion channels in the membranes of the stereocilia • Motile response- A response by outer hair cells that magnifies the movements of the basilar membrane, amplifying sounds and sharpening the response to particular frequencies • Place code- Frequency representation based on the displacement of the basilar membrane at different locations • Temporal code- Frequency representation based on a match between the frequencies in incoming sound waves and the firing rates of auditory nerve fibers • Volley principle- The idea that each nerve fiber in a population of auditory nerve fibers produces action potentials in phase with peaks in the incoming sound wave, even if not at every peak; explains how a temporal code could represent frequencies much higher than the maximum firing rate of any individual fiber • Dynamic range- The 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 • Hearing impairment-A decrease in a person’s ability to detect or discriminate sounds, compared to the ability of a healthy young adult • Tinnitus- A persistent perception of sound, such as a ringing or buzzing, not caused by any actual sound • Audiometer- An 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 a audiogram • Audiogram-A graphical representation of auditory sensitivity to specific frequencies, compared to the sensitivity of a standard listener; used to characterize possible hearing loss • Conductive hearing impairments- Hearing impairments characterized by a loss of sound conduction to the cochlea, as a result of problems in the outer or middle ear • Sensorineural hearing impairments- Hearing impairments caused by damage to the cochlea, the auditory nerve, or the auditory areas or pathways of the brain • Presbycusis- Age-related hearing impairment. Most significant contributor to this is a life-long exposure to noise, other factors include exposure to certain industrial chemicals, smoking and alcohol abuse, diabetes and cardiovascular disease, head trauma, and poor nutrition. Might also be a genetic component • Cochlear implants- Devices designed mainly to enable deaf individuals to hear spoken language; have both external and internal components Summary • Sound o Sound is a wave of pressure changes in a medium such as air, propagating outward from a source 3 4 o The related physical and perceptual dimensions of sounds are ▪ Frequency and pitch ▪ Amplitude and loudness ▪ Waveform and timbre o An audibility curve shows the audibility threshold for any given frequency o Equal loudness contours show the amplitude that sounds of different frequencies must have to be perceived as having the same loudness o A periodic sound wave can be decomposed by Fourier analysis into a Fourier spectrum o Timbre depends mainly on which harmonics are present in the sound and on their relative amplitudes • The Ear o The ear gathers sound energy and transduces it into neural signals o The pinna funnels sound into the auditory canal and onto the tympanic membrane o The vibration of the tympanic membrane transfers the sound energy to the ossicles, which then transmit the energy onto the oval window, which sends the energy into the cochlea o The Eustachian tube can be opened to maintain normal air pressure in the middle ear o The cochlea is partitioned into 3 chambers ▪ Vestibular canal ▪ Cochlear duct ▪ Tympanic canal o The basilar membrane separates the cochlear duct and the tympanic canal and is thicker and narrower and stiffer at the base than at the apex o Pressure waves in the perilymph displace the basilar membrane to different degrees at different locations, depending on the characteristic frequency at each location o The organ of Corti contains structures involved in auditory transduction, including the inner and outer hair calles • Neural Representation of Frequency and Amplitude o Frequency is represented by both a place code and a temporal code ▪ The place code is based on the displacement of the basilar membrane to different degrees at different locations, resulting in the production of action potentials by Type 1 auditory nerve fibers connected to inner hair cells at those location, depending on characteristic frequency at each location ▪ The temporal code is based on a match between frequencies in the incoming sound wave and spike timing in auditory nerve fibers. o Place coding provides good representations of frequencies above about 5,000Hz o Temporal coding works best for lower frequencies 4 5 o Amplitude representation is based on the fact that as the amplitude of a sound increases, the firing rate of auditory nerve fibers and the number of auditory nerve fibers firing in response to the sound also increase • Disorders of Audition o In hearing tests, an audiometer presents pure tones to a listener, to determine the listener’s auditory sensitivity across a range of frequencies o The result is depicted in an audiogram, which shows the degree of hearing loss at each frequency, compared to a standard listener o Conductive hearing impairments arise because of problems in the outer or middle ear, with a loss of sound conduction to the cochlea o Sensorineural hearing impairments arise through damage to the cochlea, the auditory nerve, or the auditory areas of the brain- and are typically age related or noise induced o Exposure to loud noise can damage the cochlea mechanically and by causing the death of hair cells o Tinnitus- ringing in the ears is common and can be severe enough to disrupt daily life o Various causes and treatments of tinnitus have been found • Applications o Cochlear implants are designed primarily to help deaf or severely impaired people to hear speech o The external components of a cochlear implant consist of ▪ Microphone ▪ Sound processor ▪ Transmitter o The internal components of a cochlear implant consist of ▪ Receiver-stimulator ▪ Electrode system that spirals around the cochlea and stimulates auditory nerve fibers, using both place coding and temporal coding o For children born deaf, cochlear implants tend to work better when implanted at an earlier age, during the critical period for acquiring language Reading • Meniere’s disease- caused by a buildup of fluid in the parts of the ear that support both hearing and balance • Sound o Physically sound is nothing more than changes in pressure over time, transmitted in a medium such as air or water o Sources of sound ▪ Sound is usually initiated by movement that disturbs air molecules, causing them to collide with other air molecules, resulting in changes in air pressure that propagate outward from the source ▪ The air molecules oscillate back and forth, but the waves of pressure changes, called sound waves, can be detected from far distances 5 6 ▪ The horizontal line labeled “Normal air pressure” marks the air pressure in the absence of sound ▪ One cycle of the sound wave is a repeating segment of air pressure changes ▪ The sound energy at any given point on the wave decreases with distance from the source ▪ The Falloff in sound energy with distance is an example of an inverse square law, because the energy of the sound decreases in proportion to the square of the distance from the source o Physical and Perceptual Dimensions of Sound ▪ 3 most important physical dimensions are frequency, amplitude, and waveform ▪ 3 most important perceptual dimensions are pitch, loudness, and timbre (sound quality) ▪ Periodic sound waves- waves in which the cycles of compression and rarefaction repeat in a regular fashion ▪ Aperiodic wave- associated with an abrupt or turbulent event such as slamming a door or a roll of thunder ▪ Simpliest periodic wave is a pure tone • Pure tone- a sound wave in which air pressure changes overtime according to a mathematical formula called sine wave or sinuoid ▪ Frequency and Pitch • Frequency- the physical dimension • Pitch- the perceptual dimension • Tones with a high frequency sound high pitched- • Tones with low frequency sound low pitched- Tuba • Frequency expressed in hertz (Hz) • People with unimpaired hearing can detect a range from about 20-20,000 Hz ▪ Amplitude and Loudness • Amplitude- the difference between the maximum and minimum sound pressure in the wave- the physical dimension • Loudness- how intense or quiet a sound seems- the perceptual dimension • Periodic sounds that aren’t pure tones (such as the human voice) have peaks and troughs that vary in height, in which some case the peak amplitude within some time interval is defined as the largest peak-to-trough difference during that interval • Amplitude is measured in decibels (dB) • The relationship between decibels and sound pressure is logarithmic o dB SPL = 20 log (p/p )0 o p is the measured sound pressure in micropascals 6 7 o p i0 a standard (20) • As the physical amplitude of a sound doubles, the perceived loudness increases by a constant amount, no matter whether the sound is doubling from a low level or high level • The JND in intensity of a sound is about 1 dB, whether the change is made from a quiet sound or loud sound • 0dB SPL corresponds to the threshold of hearing for healthy young adults • Sound with a physical sound pressure of less than 20 mPa are i
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