cae 334/502 lecture 3b from spring 2014
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CAE 334/502Lecture 3a
The Human Auditory System
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Last Time
Simple Sources Point, Line, and Plane
Sound PowerSound Pressure Levelrelations
The Acoustic Spectrum
Frequency Bands
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This Time
Auditory System Outer, Middle, Inner Ears
Hearing Loss
Conductive and Neurosensory
Scary Pictures
Harmful Levels
What you can do for your ears.
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For Next Time
Read Chapter 3 of LAA if you havent Read Chapter 4, 5 and 6.1 (Resonance)
More Acoustics Journals
No Homework Next Week!
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References
LAA Chapter 3.1
Daniel Raichel, The Science and Applicationof Acoustics, Springer-Verlag, 2000
Jens Blauert, Spatial Hearing, The
psychophysics of human sound localization,Fevised Edition, MIT Press, 1999
Fettiplace, R., and Hackney, C. M. (2006)."The sensory and motor roles of auditory hair
cells," Nature Reviews Neuroscience 7, 19-29.
http://www.neurophys.wisc.edu/animations/
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Objectives
Understand the basic regions of the auditorysystem
Understand the function of the three mainregions
Understand how noise can induce hearingloss
Understand that NIHL is permanent
Understand what you can do to reduce yourrisk of NIHL
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The Auditory System
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Outer Ear
Pinna or Aurical
Collects Sound Diffracts Sound
Very important to soundlocalization
Ear Canal
(meatus acusticus) Takes sound to ear drum
Eardrum
(Tympanic Membrane) Thin diaphragm
Moves with air pressureoscillations
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Outer ear as amplifier
Speech frequency soundsare amplified by the outerear Pinnae reflect and diffract
sound Ear canals resonate
Result: 1015 dB ofamplification from 2-5 kHz
Amplification is directiondependent
Pinnae diffraction is freq.dependent Helps us localize sound
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Middle Ear
Malleus, Incus, Stapes
(hammer, anvil, stirrup) 3 smallest bones in body Acts as impedance matching
device to transmit acousticenergy into inner ear
Tympanic Muscle Acoustic Reflex reduces
bone motion up to 20 dB offor protection at low freq
Eustachian Tube Equalizes air pressure Drains infection
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Middle ear as a filter
The middle ear attenuates high and lowfrequencies quite a bit
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Inner Ear
Semicircular Canals Used for balance and nothearing
Oval Window Receives vibrations of
stapes and transmits tocochlear fluid andmembranes
Cochlea spiral shaped cavity that has
fluids and membraneswhich convert sound tonerve impulses
Cochlear nerve Transmits audio signals to
and from the brain
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Unrolled Cochlea
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Organ of Corti
Organ of corti lies on
basilar membrane thatruns down the center ofthe cochlea
Contains inner hair cells(IHC) and outer hair
cells (OHC) that movewith fluid motion
IHC just respond tosound while OHC helpto control fluid motion atthe IHC as well asrespond to sound
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IHC and OHC OHC change length to attenuate modify
fluid motion near IHC to attenuate oramplify the IHC response
IHC flex in response to sound and themechanical linkage between cilia ( tip
links) mechanically open ion channelgates which generate nerve impulses
Top links can be severed and the tall ciliacan fuse or break in response to excessive
sound levels meaning neural responsedrops or is eliminated (i.e. you go deaf)
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OHC as an Active Element
When the brain requiresbetter frequencyselectivity, it cause theOHC to contract and move
the tectorial and basilarmembrane with the properphasing to alter the fluidmotion at the IHC
This is, in essence, apositive feedback system
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Frequency Selectivity
Since the brain can activateOHC in only certain sectionsif it wants, only thosefrequencies get amplifiedand so the OHC can act asa narrow band amplifier toselect sounds at certainfrequencies.
When OHC get damaged, the OHC can no longerprovide frequency selectivity and sensitivityenhancement. This means hearing is compromised. Dashed line is selectivity with OHC loss Solid lines are selectivity without OHC loss
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Tip Links on IHC
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So, that is how you hear.
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Our Fragile Inner Ears
As we just saw, auditory physiology is verycomplex with a lot of tiny, fragile, andinterdependent parts.
It does not take much work to destroy parts ofthe system, reducing the sensitivity of hearing(i.e. creating a hearing loss)
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Types of Hearing Loss
Damage to the Eardrum (conductive loss)
Usually from something puncturing it, sometimes froma bad middle ear infectionnot noise
This can heal
Damage to middle ear bones (conductive loss)
This comes from head trauma or with agingnot noise
This can heal or be healed with surgery
Damage to the inner ear (neuro-sensory loss)
This comes from loud noises, drugs, or chemicals This damage usually does not heal (ever!) and cannot
be corrected with surgery.
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Neurosensory Hearing Loss
1. Temporary Threshold Shift A temporary reduction in hearing sensitivity that
occurs from biochemical overload
When the ion-channels get a chance to recover,normal hearing is restored. This can take
minutes to hours2. Permanent Threshold Shift or Noise Induced
Hearing Loss (NIHL) A permanent reduction in hearing sensitivity that
occurs from damage to inner ear hair cells There is no recovery, damage is permanent.
Really. Really, Really. No Kidding.
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Tinnitus
Tinnitus is a ringing or buzzing in the ears.
It may be constant, it may come and go
Most common cause is NIHL
90% of members of American tinnitus association also havehearing loss
The cause of the actual ringing could be: Physiological where the auditory nerves continue to fire
after sound is gone
OHC keep trying to control noise that isnt there and
actually generate true noise that the IHC measure Mental where the brain thinks the auditory nerves are
sending impulses
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How Loud Noise Damages Inner Ears
Loud noises can breakthe tip links
Louder noises can breakthe taller cilia in half
Really loud noise canbreak cilia at their base
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Once destroyed, the broken tip links andcilia will notheal. Ever. The damage to theinner ear hair cells is permanent.
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Damaged OHC
The top figure shows anundamaged chinchilla ear. Wecan clearly see three rows ofOHC cilia.
The bottom figure showsdamage. The three OHC ciliahave been destroyed whenexposed to noise levels typical
of a construction site (there isa bit left)
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More Damaged OHC
Top (a) is normal OHCand IHC and bottom(b) is damaged OHCand IHC.
Exposure time was notgiven but damage toOHC and IHC isclearly significant andwidespread
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Figure from Ryan, A. (2000). "Protection of auditory
receptors and neurons: Evidence for interactive damage,"
Proceedings of the National Academy of Sciences 97, 6939.
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Audio Examples Of Hearing Loss
Audio Examples of hearing loss Normal Hearing
Moderate Hearing Loss (playing your ipod too loud fora few years
Severe Hearing Loss (playing your ipod too loud for
most of your life)
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Implant Normal
Speech
Music
Cochlear Implants
People with damagedinner ears can getcochlear implants
Cochlear implants onlyproduce rudimentaryhearing that works okayfor speech but not formusic
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4 Channel Cochlear Implant Demos taken from
http://www.hei.org/research/aip/audiodemos.htm
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More Simulations
Here are some good web sites with furthersimulations of hearing loss and treatmentssuch as cochlear implants
Hearing Loss Sampler
Hearing Loss + Tinnitus Simulator Cochlear Implant Simulations
Hearing Loss Simulation Software
NIOSH Hearing Loss Simulator
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http://facstaff.uww.edu/bradleys/radio/hlsimulation/http://www.sens.com/helps/demo02/helps_d02_S1_HF2k_70.htmhttp://www.healthaffairs.uci.edu/hesp/Simulations/simulationsmain.htmhttp://www.phon.ucl.ac.uk/resource/hearloss/http://www.cdc.gov/niosh/mining/works/coversheet1820.htmlhttp://www.cdc.gov/niosh/mining/works/coversheet1820.htmlhttp://www.phon.ucl.ac.uk/resource/hearloss/http://www.healthaffairs.uci.edu/hesp/Simulations/simulationsmain.htmhttp://www.sens.com/helps/demo02/helps_d02_S1_HF2k_70.htmhttp://facstaff.uww.edu/bradleys/radio/hlsimulation/ -
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Immediate signs of hearing damage
Damage Signs Ringing in the ears
Headache
Feeling Tired (fatigue)
If you experience thesesymptoms get out of thenoise right away. If the symptoms go away
in 15 minutes or so youare probably okay.
If it takes longer you mayhave some permanenthearing damage
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What levels to avoid (from NIOSH)
Long term exposure to high sound levels
85 dB for more than 8 hours per day
88 dB for more than 4 hours per day
91 dB for more than 2 hours per day
94 dB for more than 1 hours per day 97 dB for more than hour per day
100 dB for more than 15 min per day
Rock concerts have sustained levels well inexcess of 100 dB for more than 15 min. Dont
become a roadie without hearing protection.
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What can you do? Protect yourself!
Ear Muffs Easily removed when needed Prove 25-35 dB of protection Cost $25-$50 each
Foam protectors 30-40 dB of protection $0.25-$10.00 a pair in bulk Proper insertion must be taught
for most types Molded protectors
30-40 dB of protection
$50-$200 each Very comfortable even for
extended periods of time
http://www.earinc.com/p1-nonelectronic-instamold.phphttp://www.discountsafetygear.com/ear-protection-ear-muffs.htmlhttp://www.discountsafetygear.com/ear-protection-ear-plugs.html -
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Musicians Earplugs
Musicians plugs 15-25 dB of protection with a flatter
frequency attenuation than foam
$10-$20/pair
$150-$200 for custom molded
Search for foam earplug or musiciansearplug on google
I get my earplugs athttp://www.earplugstore.com
If you are a frequent listener of live musicyou reallyneed to get a pair!
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What about my i-pod?
Use noise isolating earphones! These provide good sound isolation (10-20 dB) so you dont needto turn up the volume to drown out the background noise
My favorites (this is a few years old so its out of date) Etymotic (ER4, ER6, ER6i) (Ive got the ER6i)
Shure (E2c, E3c, E4c, E5c)
Altec Lancing (im616 and 716 are Etymotic ER6 clones, I got theim616 on sale on Amazon for $45)
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To get your hearing tested
See an audiologist
UIC, Rush, and Northwestern all have audiologyprograms and sometimes offer affordable or free testing Online:
http://www.phys.unsw.edu.au/jw/hearing.html http://www.digital-recordings.com
http://myhearingtest.net/ http://www.starkey.com/online-hearing-test http://www.hear-the-world.com
Software: http://www.audiometer.co.uk/
Free with sales pitch (for a hearing aid) http://www.miracle-ear.com/en-us/ Simple Questionnaire
http://www.betterhearing.org/check-your-hearing
http://www.phys.unsw.edu.au/jw/hearing.htmlhttp://www.digital-recordings.com/http://myhearingtest.net/http://www.starkey.com/online-hearing-testhttp://www.hear-the-world.com/en/hearing-and-hearing-loss/online-hearing-test.htmlhttp://www.audiometer.co.uk/http://www.miracle-ear.com/en-us/http://www.betterhearing.org/check-your-hearinghttp://www.betterhearing.org/check-your-hearinghttp://www.betterhearing.org/check-your-hearinghttp://www.betterhearing.org/check-your-hearinghttp://www.betterhearing.org/check-your-hearinghttp://www.betterhearing.org/check-your-hearinghttp://www.miracle-ear.com/en-us/http://www.miracle-ear.com/en-us/http://www.miracle-ear.com/en-us/http://www.miracle-ear.com/en-us/http://www.miracle-ear.com/en-us/http://www.miracle-ear.com/en-us/http://www.audiometer.co.uk/http://www.hear-the-world.com/en/hearing-and-hearing-loss/online-hearing-test.htmlhttp://www.hear-the-world.com/en/hearing-and-hearing-loss/online-hearing-test.htmlhttp://www.hear-the-world.com/en/hearing-and-hearing-loss/online-hearing-test.htmlhttp://www.hear-the-world.com/en/hearing-and-hearing-loss/online-hearing-test.htmlhttp://www.hear-the-world.com/en/hearing-and-hearing-loss/online-hearing-test.htmlhttp://www.starkey.com/online-hearing-testhttp://www.starkey.com/online-hearing-testhttp://www.starkey.com/online-hearing-testhttp://www.starkey.com/online-hearing-testhttp://www.starkey.com/online-hearing-testhttp://myhearingtest.net/http://www.digital-recordings.com/http://www.digital-recordings.com/http://www.digital-recordings.com/http://www.phys.unsw.edu.au/jw/hearing.html -
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For More Info
Here are some useful web sites http://en.wikipedia.org/wiki/Auditory_system
http://www.asha.org/public/hearing/disorders/default.htm
http://www.ata.org/
http://www.hearinglossweb.com/
http://www.osha.gov/SLTC/noisehearingconservation/index.html
http://www.cdc.gov/niosh/topics/noise/
http://www.euro.who.int/Noise
http://www.nonoise.org
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http://en.wikipedia.org/wiki/Auditory_systemhttp://www.asha.org/public/hearing/disorders/default.htmhttp://www.ata.org/http://www.hearinglossweb.com/http://www.osha.gov/SLTC/noisehearingconservation/index.htmlhttp://www.cdc.gov/niosh/topics/noise/http://www.euro.who.int/Noisehttp://www.nonoise.org/http://www.nonoise.org/http://www.euro.who.int/Noisehttp://www.cdc.gov/niosh/topics/noise/http://www.osha.gov/SLTC/noisehearingconservation/index.htmlhttp://www.hearinglossweb.com/http://www.ata.org/http://www.asha.org/public/hearing/disorders/default.htmhttp://en.wikipedia.org/wiki/Auditory_systemhttp://en.wikipedia.org/wiki/Auditory_systemhttp://en.wikipedia.org/wiki/Auditory_system -
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Its Really Pretty Simple..
Wear this now... Or wear this later!
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A final note on noise
This is your ear. This is your ear on noise.
Any questions?
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