PSYB51H3 Chapter Notes - Chapter 9: Middle Ear

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Published on 12 May 2011
School
UTSC
Department
Psychology
Course
PSYB51H3
Chapter 9: Hearing: Physiology and Psychoacoustics
The Function of hearing
Loudness and pitch are fundamental sound qualities
Each sense developed at diff time to diff challenges
What is Sound?
Sound created when objects vibrate
oObject vibration medium molecule vibration Medium pressure change
Medium e.g. Earths atmosphere
As distance, pressure pattern but amt of pressure 
oE.g. Fig. 9.1
Speed of sound wave depends on medium
odensity, speed 
e.g. sound through air is 350m/s vs. air 1500 m/s
sonic boom is when speed catches up to front of sound waves
Basic Qualities of Sound Waves: Frequency and Amplitude
amplitude: amt of pressure change
odefines loudness (perceived intensity)
intensity, loudness 
intensity: amt of sound energy on area
frequency: time/s pressure fluctuates
odefines pitch
freq, pitch 
oin waves, space between each wave
Hertz (Hz): measure of freq.
o1 Hz = 1 cycle/s
Humans can hear from 20 to 20,000 Hz approx
Decibels (dB): measure physical intensity of sound. Uses ratio btw 2 sound
pressure
oe.g. 10: 1 sound ratio = 20dB, where 1 is faintest sound heard
dB = 20 log (p/po)
owhere p = intensity
op0 = ref pressure, 0.0002 dyne/cm2
Sine Waves, Complex Tones, and Fourier Analysis
sine waves/pure tone: Waveform, variation as fn of t is sine fn
oair pressure changing continuously but with same freq
period: time for 1 cycle of sine wave
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phase: relative position of 2 or more sine waves
o360 degrees of phase across 1 period
Most things are complex tones
Complex tones: sound wave that has more than 1 sinusoidal component of diff
frequencies
Sound is like combination of sine waves
Fourier Analysis: math thereom, describes individual sine waves of complex
sounds
Spectrum: graph of intensity at each freq
oE.g. Fig. 9.7
Harmonic spectrum: spectrum of complex sound, same fundamental freq but with
different amplitudes
oE.g instruments all playing middle C, but sound diff b/c of diff amplitudes
Fig. 9.8
oEach frequency called harmonic
Fundamental frequency: lowest freq component of complex sound
oAll other harmonics are integer multiples of this
Timbre: Quality of sound that depends on energy levels of harmonics
Basic Structure of the Mammalian Auditory System
Outer Ear
Pinna: outer funnel-like part of the ear
oSound first collected here
oOnly mammals have pinnae
Ear canal: canal that sends sound vibration from pinna to tympanic membrane
oPrevents damage to tympanic membrane
Tympanic membrane (eardrum): Thin sheet of skin, responds to pressure
changes of sound waves by moving in and out
Middle Ear
Outer ear: external sound gathering part of ear
oMade of pinna and ear canal
Tympanic membrane is border btw middle and outer ear
Middle ear: air filled chamber containing ossicles (middle bones)
oSends and amplifies vibration from tympanic membrane to oval window
Ossicles: 3 tiny bones malleus, incus and stapes
oAmplify sound waves
oMalleus: connected to tympanic membrane and incus
oIncus: middle ossicle, connects malleus to stapes
oStapes: sends vibrations of sound waves to oval window
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Connected to incus and oval window of cochlea
Oval window: flexible opening to cochlea
oStapes sends vibration to fluid inside
oBorder btw middle ear and inner ear
oInner ear: hollow cavity in temporal bone of skull and its structures
cochlea and vestibular canals
Ossicles energy sent to inner ear by:
otaking little energy on 1 side of joint, and making into large amt
Joints between ossicle bones are like levers, push on each other
osends energy from larger surface area to smaller
sends from tympanic membrane to oval window (pressure is 18x)
1.malleus
incus
2.stapes
3.oval window
need amplification to move fluid in inner ear, direct sound waves not enough
middle ear has to muscles tensor tymani and stapedius
otensor tymapni: muscle attached to malleus
tensing vibration
ostapedius: muscle attached to stapes
tensing vibration
acoustic reflex: reflex that protects ear from intense sounds
ouses strapedius and tensor tympani
odelayed by 1/5 of second so doesnt help with abrupt noises
oalso blocks out body noises e.g. swallowing, talking etc.
Inner Ear
transforms changes in sound pressure into neural signals
COCHLEAR CANALS AND MEMBRANES
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