Through a series of sonic illusions, scientists have found that from a cognitive perspective people perceive silence similarly to how they perceive sounds.
Can we hear the sound of silence? Or is silence the mere absence of sounds? Despite centuries of contemplation, these questions have remained elusive. However, in a recent study, researchers took a scientific approach to the debate, and their findings suggest that silence is, in fact, a sound.
Historically, the nature of silence has been divided into two perspectives. The perceptual view and the cognitive view. The perceptual view contends that we actually hear silence, while the cognitive view posits that we merely judge or infer its presence from the absence of other sounds.
“So far, until our research [came about] there had not been a key empirical test for this question. And so that's what we sought to provide,” says Rui Zhe Goh, a co-author of the study and graduate student in cognitive science and philosophy at Johns Hopkins University.
To put silence to the test, Goh and his professors worked on a series of sonic illusions to see if people perceive silence as they hear sounds, from a cognitive perspective.
“So our strategy was to test if some of the auditory illusions that happen with sound also happen with silence,” he told Euronews Next.
Like optical illusions that trick what people see, auditory illusions can make people hear sounds as being longer or shorter than they actually are. One example is the one-is-more illusion, where one long beep seems longer than two short consecutive beeps - even when the two sequences are equally long.
In tests involving 1,000 participants, and to empirically test the nature of silence, the team swapped the sounds typical of the one-is-more illusion with moments of silence, reworking the auditory illusion into what they dubbed the “one-silence-is-more illusion”.
The one-silence-is-more illusion presented participants with audiotracks replicating bustling environments like restaurants, markets, and train stations. And within these, the team inserted moments of sudden cessation, resulting in brief silences. The participants were then asked to measure, in length, which one of the silences was longer - despite both being of the same duration.
The results, published in the scientific journal PNAS, were surprising, says Goh.
People thought one long moment of silence was longer than two short moments of silence. In other words, the one-silence-is-more illusion yielded the same outcomes as the original one-is-more illusion.
“I was like, wow, this actually works. I mean, I made it, I programmed it, and I knew that the durations of the silence sequences were the same length, but when I heard it, it definitely sounded like the one silent sequence was longer,” Goh says.
The fact that these silence-based illusions produced exactly the same results as their sound-based counterparts suggest that people hear silence just as they hear sounds, because it implies a similar cognitive processing between the two.
"Our approach was to ask whether our brains treat silences the way they treat sounds. If you can get the same illusions with silences as you get with sounds, then that may be evidence that we literally hear silence after all," said Chaz Firestone, an assistant professor of psychological and brain sciences who directs the Johns Hopkins Perception & Mind Laboratory in a statement.
“The same cognitive processing that happens with sound is also triggered by moments of silence. And given that the auditory system treats these moments of silence just like a sound, this suggests that we can have auditory experiences of silence,” Goh explains.
The results might explain “why when you are walking down a busy street, and you walk inside a quiet space, you are kind of hit by the silence, and why the moments of silence during a theatrical performance or a musical piece exert such a strong force,” he adds.
"There's at least one thing that we hear that isn't a sound, and that's the silence that happens when sounds go away," said co-author Ian Phillips, a Bloomberg Distinguished Professor of Philosophy and Psychological and Brain Sciences, in a statement.
"The kinds of illusions and effects that look like they are unique to the auditory processing of a sound, we also get them with silences, suggesting we really do hear absences of sound too," he added.
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 future of the sound of silence
The researchers plan to keep exploring the extent to which people hear silence, including “what we might call pure silence, which are silences that are not heard in contrast to sound”.
“So, the silences you might hear during meditation or when you are looking out the window and listening to the quiet night,” said Goh.