[Paleopsych] MSNBC: How the brain tunes out background noise

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Fri Dec 30 19:31:01 UTC 2005

How the brain tunes out background noise

    'Detector neurons' focus exclusively on novel sounds, scientists

    Special neurons in the brain stem of rats focus exclusively on
    novel sounds and help them ignore predictable and ongoing noises, a
    new study finds.

    The same process likely occurs in humans and may affect our speech,
    and even help us laugh.

    The "novelty detector neurons," as researchers call them, quickly
    stop firing if a sound or a pattern of sounds is repeated. They
    will briefly resume firing if some aspect of the sound changes. The
    neurons can detect changes in pitch, loudness or duration of a
    single sound and can also note shifts in the pattern of a complex
    series of sounds.

    "It is probably a good thing to have this ability, because it
    allows us to tune out background noises like the humming of a car's
    motor while we are driving or the regular tick-tock of a clock,"
    said study team member Ellen Covey, a psychology professor at the
    University of Washington. "But at the same time, these neurons
    would instantly draw a person's attention if their car's motor
    suddenly made a strange noise or if their cell phone rang."

    Covey said similar neurons seem to be present in all vertebrates
    and almost certainly exist in the human brain.

    The novelty detector neurons seem to act as gatekeepers, Covey and
    her colleagues conclude, preventing information about unimportant
    sounds from reaching the brain's cortex, where higher processing
    occurs. This allows people to ignore sounds that don't require

    The results are detailed this month in the European Journal of

    The novelty detector neurons seem able to store information about a
    pattern of sound, so they may also be involved in speech, which
    requires anticipating the end of a word and knowing where the next
    one begins.

    "Speech fluency requires a predictive strategy," Covey explained.
    "Whatever we have just heard allows us to anticipate what will come
    next, and violations of our predictions are often surprising or

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