cae 334/502 lecture 3b from spring 2014

8/12/2019 CAE 334/502 Lecture 3b from Spring 2014

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2/16/2014 CAE 334/502 - Week 4 1

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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http://www.hei.org/research/aip/audiodemos.htmhttp://www.hei.org/research/aip/audiodemos.htmhttp://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



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!
http://www.earplugstore.com/http://www.earplugstore.com/


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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?

cae 334/502 lecture 3b from spring 2014

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