How We Hear The (Disappearing) Sound Of Silence

What with turbo engines, screeching sirens, and honking cars encroaching on most of the world’s remaining quiet places, silence is a rare and precious commodity today – a natural resource, if you will. Its depletion is messing with our concentration levels, cognitive functioning, happiness, and general wellbeing. Books have been written about the problem: Acoustic ecologist and author Gordon Hempton recently booked it back and forth across America in an exhaustive search of silence, and came up with just one spot (nestled in Olympic National Park) in our entire country where purely natural sound could be heard.

So of course it’s now – just as our last silent places are vanishing – that scientists discover how exactly it is that the brain hears silence. Researchers at the University of Oregon recently found that the brain’s auditory cortex actually (contrary to neurologists’ previous understanding) contains not one but two separate synapse channels for sound: one for dealing with the “turning on” of sounds, so to speak, and one for the “turning off.” In other words, there is no overlap between the synapses that help us process the onset of a sound and the synapses that help us process the disappearance of a sound.


From University of Oregon psychology professor Michael Wehr:  "Being able to perceive when sound stops is very important for speech processing. One of the really hard problems in speech is finding the boundaries between the different parts of words. It is really not well understood how the brain does that." His team’s new findings (done with lab rats – sorry, PETA) could lead to new developments in speech therapy for those – including dyslexics and kids with delayed reading skills – who have trouble locating boundaries between spoken words.

But Wehr's research also raises an interesting question from an ecopsychology standpoint:  as silence and quiet disappear, and noise pollution increasingly instructs our neurological functioning, will we evolve to match the racket? Will our brains compensate for all the noise by overdeveloping the “sound onset” synapses and under-developing the “sound off” synapses? Could our ability to process sound – or even our patterns of speech – be affected?

Simon and Garfunkel may have gotten it backwards. As the song goes:

“Fools,” said I, “you do not know / silence like a cancer grows.”

Turns out it was noise, not silence, that would grow like a cancer during the two singers’ lifetimes.

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