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The science of hearing - Douglas L. Oliver

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    You hear the gentle lap of waves,
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    the distant cawing of a seagull.
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    But then an annoying whine
    interrupts the peace,
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    getting closer, and closer, and closer.
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    Until...whack!
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    You dispatch the offending mosquito,
    and calm is restored.
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    How did you detect that noise from afar
    and target its maker with such precision?
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    The ability to recognize sounds
    and identify their location
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    is possible thanks to the auditory system.
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    That’s comprised of two main parts:
    the ear and the brain.
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    The ear’s task is to convert sound energy
    into neural signals;
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    the brain’s is to receive and process
    the information those signals contain.
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    To understand how that works,
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    we can follow a sound
    on its journey into the ear.
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    The source of a sound creates vibrations
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    that travel as waves of pressure
    through particles in air,
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    liquids,
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    or solids.
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    But, our inner ear, called the cochlea,
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    is actually filled
    with saltwater-like fluids.
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    So, the first problem to solve
    is how to convert those sound waves,
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    wherever they’re coming from,
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    into waves in the fluid.
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    The solution is the eardrum,
    or tympanic membrane,
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    and the tiny bones of the middle ear.
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    Those convert the large movements
    of the eardrum
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    into pressure waves
    in the fluid of the cochlea.
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    When sound enters the ear canal,
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    it hits the eardrum and makes it vibrate
    like the head of a drum.
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    The vibrating eardrum jerks a bone
    called the hammer,
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    which hits the anvil and
    moves the third bone called the stapes.
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    Its motion pushes the fluid
    within the long chambers of the cochlea.
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    Once there,
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    the sound vibrations have finallly
    been converted into vibrations of a fluid,
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    and they travel like a wave
    from one end of the cochlea to the other.
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    A surface called the basilar membrane
    runs the length of the cochlea.
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    It’s lined with hair cells that have
    specialized components
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    called stereocillia,
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    which move with the vibrations of the
    cochlear fluid and the basilar membrane.
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    This movement triggers a signal
    that travels through the hair cell,
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    into the auditory nerve,
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    then onward to the brain,
    which interprets it as a specific sound.
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    When a sound makes
    the basilar membrane vibrate,
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    not every hair cell moves -
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    only selected ones,
    depending on the frequency of the sound.
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    This comes down to some fine engineering.
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    At one end,
    the basilar membrane is stiff,
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    vibrating only in response to short
    wavelength, high-frequency sounds.
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    The other is more flexible,
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    vibrating only in the presence of longer
    wavelength, low-frequency sounds.
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    So, the noises made by the seagull
    and mosquito
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    vibrate different locations
    on the basilar membrane,
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    like playing different keys on a piano.
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    But that’s not all that’s going on.
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    The brain still has another
    important task to fulfill:
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    identifying where a sound is coming from.
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    For that, it compares the sounds
    coming into the two ears
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    to locate the source in space.
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    A sound from directly in front of you will
    reach both your ears at the same time.
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    You’ll also hear it at the same intensity
    in each ear.
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    However, a low-frequency sound
    coming from one side
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    will reach the near ear microseconds
    before the far one.
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    And high-frequency sounds will sound
    more intense to the near ear
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    because they’re blocked
    from the far ear by your head.
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    These strands of information
    reach special parts of the brainstem
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    that analyze time and
    intensity differences between your ears.
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    They send the results of their
    analysis up to the auditory cortex.
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    Now the brain has
    all the information it needs:
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    the patterns of activity
    that tell us what the sound is,
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    and information about
    where it is in space.
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    Not everyone has normal hearing.
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    Hearing loss is the third most common
    chronic disease in the world.
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    Exposure to loud noises
    and some drugs can kill hair cells,
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    preventing signals from travelling
    from the ear to the brain.
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    Diseases like osteosclerosis freeze
    the tiny bones in the ear
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    so they no longer vibrate.
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    And with tinnitus,
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    the brain does strange things
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    to make us think there’s a sound
    when there isn’t one.
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    But when it does work,
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    our hearing is an incredible,
    elegant system.
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    Our ears enclose a fine-tuned piece
    of biological machinery
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    that converts the cacophony of vibrations
    in the air around us
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    into precisely tuned electrical impulses
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    that distinguish claps, taps,
    sighs, and flies.
Title:
The science of hearing - Douglas L. Oliver
Speaker:
Douglas L. Oliver
Description:

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Video Language:
English
Team:
closed TED
Project:
TED-Ed
Duration:
05:18
Michelle Mehrtens edited English subtitles for The science of hearing
Michelle Mehrtens edited English subtitles for The science of hearing
Michelle Mehrtens edited English subtitles for The science of hearing
Michelle Mehrtens edited English subtitles for The science of hearing
Michelle Mehrtens edited English subtitles for The science of hearing
Michelle Mehrtens approved English subtitles for The science of hearing
Michelle Mehrtens accepted English subtitles for The science of hearing
Michelle Mehrtens edited English subtitles for The science of hearing
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