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Chapter 9

Chapter 9

5 Pages
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Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier

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Chapter 9: Hearing: Physiology and Psychoacoustics
What Is Sound?
Sounds created when objects vibrate
Vibrations of object cause molecules in objects surrounding medium to vibrate as well
oVibration causes pressure changes in medium
oPressure changes are waves
Sound waves travel at particular speed depending on medium, moving faster through denser substances
When jet plane travels faster than speed of sound, plane catches up to and passes fronts of sound waves it
is creating
oSound waves combine into shock wave, or huge pressure fluctuation
oWhen shock wave reaches ground, we hear sonic boom
Basic Qualities of Sound Waves: Frequency and Amplitude
Amplitude (intensity): magnitude of pressure change in sound wave- difference between highest pressure
area and lowest pressure area
Pressure fluctuations can be very close together or spread apart over longer periods
Frequency: how quickly pressure fluctuates
Hertz (Hz): measure for frequency. 1 Hz equals one cycle per second
Amplitude associated with loudness: the more intense a sound wave is, the louder it will sound
Frequency associated with pitch: low-frequency sounds correspond to low pitches and high-frequency
sound correspond to high pitches
If young and careful about exposure can hear from 20 to 20 000Hz
Decibels (dB): measure for physical intensity of sound
oDefine difference between 2 sounds as ratio between 2 sound pressures
oEach 10:1 sound pressure ratio equals 20dB and 100:1 ratio equals 40dB
Sine Waves, Complex Tones, Fourier Analysis
Sine wave (pure tone): simplest kinds of sounds
oAir pressure in sine wave changes continuously at same frequency
Period: time taken for one complete cycle of sine wave
Phases: relative position of 2 or more sine waves
Complex tones: sound wave consisting of more than one sinusoidal component of different frequencies
oHuman voices, birds
Fourier analysis: individual sine wave components of complex sound
oSpectrum: shows intensity of each sine wave frequency found in complex tone
Summarize results of Fourier
Harmonic spectra: typically caused by simple vibrating source
oi.e. string of guitar or reed of saxophone
oeach frequency component in such sound called harmonic
Fundamental frequency: lowest frequency component of sound
Timbre: describe the quality of sound that depends on relative energy levels of harmonic components
Basic Structure of Mammalian Auditory System
Outer Ear
Sounds collected from environment by pinna: curly structure on side of head that we typically call ear
Only mammals have pinnae
Ear canal: sound waves funnelled by pinna into and through canal
oLength and shape of ear canal enhance sound frequencies between 2000 and 6000 Hz
oMain purpose to insulate structure at end tympanic membrane (eardrum) from damage
Damaged eardrum will heal itself, like skin
Pinna and ear canal makes outer ear
www.notesolution.com
Middle Ear
Tympanic membrane border between outer ear and middle ear
Consists of 3 tiny bones, ossicles: amplifies sound waves:
oMalleus: receives vibration from tympanic membrane on one side and connect to second ossicle
oIncus: connect to stapes
oStapes: transmits vibrations of sound waves to oval window: membrane, border between middle
and inner ear
Ossicles amplify sound vibrations in 2 ways:
oJoints between bones are hinged in way that makes then work like levers
Modest amount of energy on one side of fulcrum (joint) becomes larger on other
Lever action increases amount of pressure change by about a third
oConcentrating energy from larger to smaller surface area
Tympanic membrane, which moves malleus about 18 times as large as oval window,
which moved by stapes
Pressure on oval window magnified 18 times relative to pressure on tympanic membrane
Inner ear made up of fluid-filled chambers
Middle ear has 2 muscles:
oTensor tympani: attached to malleus
oStapedius: attached to stapes
Both are smallest muscles in body
Main purpose to tense when sounds are very loud, restricting movement of ossicles, thus
muffling pressure changes that might be large enough to damage delicate structures in
inner ear
Acoustic reflex: protects ear from intense sounds, via contraction of stapedius and tensor tympani
muscles
oFollows onset of loud sounds by 1/5 of a second, cannot protect against abrupt loud sounds
Inner Ear
Fine changes in sound pressure available in environment translated into neural signals that inform
listener about world
Translates information carried by waves into neural signals
Cochlear canals and membranes
Cochlear: tiny coiled structure embedded in temporal bone of skull
Major structure of inner ear
Filled with watery fluids in 3 parallel canals:
oTympanic canal
oVestibular canal
oMiddle canal
Tympanic and vestibular canals connected by small opening: helicotrema
3 canals of cochlea separated by 2 membranes:
oReissners membrane: between vestibular canal and middle canal
oBasilar membrane: between middle canal and tympanic canal
Not really a membrane, more o a plate made up of fibres that have some stiffness
Basilar membrane forms base of cochlear partition: complex structure through which sound waves
transduced into neural signals
Vibrations transmitted through tympanic membrane and middle ear bones cause tapes to push and pull
flexible oval windows in and out of vestibular canal
oCauses waves of pressure change- traveling waves
Cochlea is closed system, pressure change cannot spread out, instead it bulges out
www.notesolution.com

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Description
Chapter 9: Hearing: Physiology and Psychoacoustics What Is Sound? Sounds created when objects vibrate Vibrations of object cause molecules in objects surrounding medium to vibrate as well o Vibration causes pressure changes in medium o Pressure changes are waves Sound waves travel at particular speed depending on medium, moving faster through denser substances When jet plane travels faster than speed of sound, plane catches up to and passes fronts of sound waves it is creating o Sound waves combine into shock wave, or huge pressure fluctuation o When shock wave reaches ground, we hear sonic boom Basic Qualities of Sound Waves: Frequency and Amplitude Amplitude (intensity): magnitude of pressure change in sound wave- difference between highest pressure area and lowest pressure area Pressure fluctuations can be very close together or spread apart over longer periods Frequency: how quickly pressure fluctuates Hertz (Hz): measure for frequency. 1 Hz equals one cycle per second Amplitude associated with loudness: the more intense a sound wave is, the louder it will sound Frequency associated with pitch: low-frequency sounds correspond to low pitches and high-frequency sound correspond to high pitches If young and careful about exposure can hear from 20 to 20 000Hz Decibels (dB): measure for physical intensity of sound o Define difference between 2 sounds as ratio between 2 sound pressures o Each 10:1 sound pressure ratio equals 20dB and 100:1 ratio equals 40dB Sine Waves, Complex Tones, Fourier Analysis Sine wave (pure tone): simplest kinds of sounds o Air pressure in sine wave changes continuously at same frequency Period: time taken for one complete cycle of sine wave Phases: relative position of 2 or more sine waves Complex tones: sound wave consisting of more than one sinusoidal component of different frequencies o Human voices, birds Fourier analysis: individual sine wave components of complex sound o Spectrum: shows intensity of each sine wave frequency found in complex tone Summarize results of Fourier Harmonic spectra: typically caused by simple vibrating source o i.e. string of guitar or reed of saxophone o each frequency component in such sound called harmonic Fundamental frequency: lowest frequency component of sound Timbre: describe the quality of sound that depends on relative energy levels of harmonic components Basic Structure of Mammalian Auditory System Outer Ear Sounds collected from environment by pinna: curly structure on side of head that we typically call ear Only mammals have pinnae Ear canal: sound waves funnelled by pinna into and through canal o Length and shape of ear canal enhance sound frequencies between 2000 and 6000 Hz o Main purpose to insulate structure at end tympanic membrane (eardrum) from damage Damaged eardrum will heal itself, like skin Pinna and ear canal makes outer ear www.notesolution.com
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