The hush at the end of the musical performance. The pause in a
dramatic speech. The muted moment when you turn off the car. What is it that we
hear when we hear nothing at all? Are we detecting silence? Or are we just
hearing nothing and interpreting that absence as silence?
اضافة اعلان
The “Sound of Silence” is a philosophical question that made for
one of Simon & Garfunkel’s most enduring songs, but it is also a subject
that can be tested by psychologists.
In a paper published last week in the Proceedings of the
National Academy of Sciences, researchers used a series of sonic illusions to
show that people perceive silences much as they hear sounds.
While the study offers no insight into how our brains might be
processing silence, the results suggest that people perceive silence as its own
type of “sound,” not just as a gap between noises.
‘The vision that was planted in my brain still remains’Rui Zhe Goh, a graduate student in cognitive science and
philosophy at Johns Hopkins University and one of the scientists involved in
the study, described a koan that he likes: “Silence is the experience of time
passing.” He said he interprets that to mean that silence is “an auditory
experience of pure time.”
That idea made him wonder whether silence, the absence of sound,
was something that we really experience, “or is silence just kind of the lack
of experience?”
Chaz Firestone, a cognitive scientist at Johns Hopkins and
another author of the study, said that if silence is “not really a sound, and
yet it turns out that we can hear it, then evidently, hearing is about more
than just sounds.”
But simply asking “Can you perceive silence?” is a difficult question.
So, the two researchers, with Ian Phillips, a philosopher, asked a different
question: Does the mind treat silence the same way it treats sounds?
‘People hearing without listening’The researchers tested people recruited online with a series of
sound illusions. The first test compared a single longer sound with two shorter
sounds. The two shorter sounds together added up to the same amount of time as
the longer sound. But when people listened to them, they perceived the single
sound as lasting longer.
To apply that illusion to silence, Goh and colleagues inverted
the test. The scientists used sounds of restaurants, busy marketplaces, trains
or playgrounds, and inserted chunks of silence for participants to compare.
The researchers supposed that if people perceive silences as
their own type of sound, then silences should be subject to the same illusion
as the sounds. One long silence should be perceived as longer than the total of
two shorter silences. But if people perceive silence as a lack of sound, the
illusion might not exist.
Other tests placed silence in different contexts to produce more
sonic illusions. In every case they tested, listeners perceived the illusion of
a period of silence being longer just as they would have perceived an illusion
of a longer sound.
“When I heard it the first time, I was like ‘Wow, it works!’”
Goh said. Even though he made the tests himself, and he knew the periods of
silence were exactly the same length, he still experienced the illusion that
one silence was longer than two.
Firestone said the illusions were just as powerful with silences
as they were with sounds. “It’s not even like, ‘Oh, it kind of works with
silences, but it’s just a lot weaker,’” he said. “No, you get the same effect.”
In other words, people react to silences the same way they react to sounds,
even though they aren’t “hearing” anything at all.
‘Hear my words that I might teach you’
It would be easy to reject the idea that silence has a sound,
said Sami Yousif, a cognitive scientist at the University of Pennsylvania who
was not involved in the study. Sounds are waves impacting the cells in your
ear. Silence is not. But that doesn’t mean we can’t detect that silence.
The study, Yousif said, shows that “those blank spaces are also
a kind of event, they are a kind of unit that is represented in our
experience.”
He also appreciated how the researcher’s used illusions tweaked
for silence instead of sound. “It is very clever in the way that it uses sort
of known phenomena, and applies them to silences instead,” he said.
Although the researchers did not study how people’s brains
responded to silence, Goh suggested that existing research supported the idea
that some neurons and neural processes were involved in the perception of
silence.
And knowing that we do perceive silence makes silence that much,
er, louder: “Silence is a real experience,” Goh said. Maybe we will all pay
more attention to moments of quiet once we know we can hear the “sounds” of
silence.
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