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Flashcards in Human Factors 3 Deck (50):
1

Sound

vibration of air molecules
-object moving back and forth compresses and rarifies air
-creates pressure that are at higher and lower atmospheric pressures
-spreads in a wave which can be graphed 2D

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amplitude

sound pressure percieved as loudness

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frequency

cycles per second (hertz) perceived as pitch

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pitch

wavelength/frequency

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condensation

air particles vibrate about a fixed point

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rarefaction

wave of vibration spreads outwards

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3 tiny bones

malleus, incus, stapes

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3 small bones

convert sound vibrations from air to fluid vibrations in the cochlea

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eardrum

tympanic memebrane

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cochlea

split into upper and lower part by basilar membrane - an elastic partition that runs from begining to end

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basilar membrane

fluid in cochlea ripples and travelling wave forms along the basilar membrane

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hair cells

sensory cells in basilar membrane that move up and down
microscopic hair-like projections (stereocilia) on top of the hair cells bump against an overlying structure and bend
bending causes channels which are at the tips of the steroeocilia to open up -chemicals rush in creating an electric signal

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auditory nerve

carries electrical signal into the brain, which translates into a sound that we recognize and understand

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hair cells and cochlea

different areas are sensitive to different frequencies - pitch
apex = 200Hz and the base = 20,000Hz

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sound intensity

acoustic intensity - sound power per unit area
watt per square meter (W/m^2)

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example decibBels

weakest sound heard - 0.0
Average home - 50
normal conversation - 60
phone dial tone - 80
Truck traffic - 90
chainsaw- 110

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sound intensity

DECIBELS

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equal intensities but different frequencies are perceived by the same person to have unequal loudness

example 60dB with freq. of 1000Hz sounds louder than 60dB with a frequency of 500Hz

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phon

used to indicate an individuals perception of loudness. Definition is 1phon = 1 dB at 1000Hz

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60-phon curve

volunteers subjected to 1kHz sound at 6dB this is the loudness of 60phon
-repeated with different frequencies

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sone

sone scale tells us how much louder one sound is than another

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interaction between sound amplitude and frequency

the sound we hear

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most sensitive tones

btw 1000-4000Hz

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Presbycusis

hearing threshold elevation at high frequencies

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noise induced hearing loss

sound can damage sensitive structures int he inner ear

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NIHL

can be temporary or permenant - can effect both or one ear can be immediate or take a while to notice

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hearing loss at work

15% OF AMERICANS have hearing loss by exposure to noise at work or leisure

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what causes NIHL

long or repeated exposure to sounds at or above 85 dB can cause hearing loss

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NIHL

most hearing loss is caused b damage and eventual death of hair cells - human hair cells don't grow back
the louder the sound the shorter amount of time it takes for NIHL to happen

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NIOSH recommendations

85 dB for eight hours to minimize occupational risk
and recommends a 3dB exchange rate so that every increase by 3 dB doubles the amount of noise and halves the recommended exposure time

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center for disease and control

also has noise recommendation

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noise contouring

sound level meters used to measure dB at different places in a space and create a sound contour map

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highest NIHL in canada

carpentry

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tinnitus

ringing or buzzing or roaring in the head when no external noise is present

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NIHL completely preventable by

know dB (above 85)
wear earplugs
move away from noise
be alert to hazardous environment
protect the ears of children
raise awareness with friends and family
have hearing tested

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temporary threshold shift (TTS)

aka auditory fatigue is exposure to continuous or impluse of noise may cause temorary hearing loss that goes away 16-48 hrs later

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TTS

in intense noise hair cells are bent and overstim leads to temporary paralysis of hair cells
hair cells will shift to recover with time away from the noise

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TTS

usually at frequencies higher than exposure frequency - usually 4000Hz

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chronic noise exposure

leads to raised cortisol levels and other stress horomones
noise exposure above 67-70dB weak correlation with hypertension

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noise levels of 50dB at night

may increase the risk of myocardial infraction

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noise also associated with

headaches , ulcers, fatigue, vertigo

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vestibular system

encodes linear and rotatory acceleration of the head
senses constant linear acceleration by earth gravity so it senses head position with respect to constant gravitational acceleration

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vestibular system

detects acceleration forces, maintains upright posture/balance and controls eye position relative to head

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semicircular canals

angular acceleration (rotation) in 3 axes
a crista embedded in jelly-like material(cupola) is supporte by hair cells that bend and fire in response to head rotation

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vestibular sacs (utricle and saccule(

hair cells in a jelly like substance lag behind when head moves - linear acceleration

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nystagmus

involuntary movement of eyes - mixture of fast and slow movements
can occur normally when tracking visual pattern
may also be abnormal and accompanied with vertigo (sensation of spinning)

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spontaneous nystagmus

presented spontaneously

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positional nystagmus

presented with a change in body position(specifically neck)

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most likely to cause damage (frequency)

low frequency - because you can listen to a lot louder (higher decibels) because it is perceived as quieter

50

age related hearing loss

the threshold is higher so you can be exposed to them longer because you perceive them as quieter