Imagine sitting in a bustling café, the clatter of dishes, the hum of conversation, and the hiss of the espresso machine all sounding in the background. Suddenly, everything goes quiet. Can you hear that silence?
It sounds like a silly question but according to a team of philosophers and psychologists, you can. That's because illusions based on silence are perceived the same as illusions with sounds. This means the brain treats silence like it does sound.
In other words, silence is not merely the absence of sound, but something we can actively perceive. So Simon & Garfunkel were right all along!
The Sound of Nothingness
Whether or not silence is a property of sound that can be perceived has been a matter of debate for many years. This puzzle has mostly entertained philosophers, but it's only recently that our perception of silence has been more rigorously tested with the scientific method.
For their new study, researchers at Johns Hopkins University used auditory illusions to demonstrate how silence can seemingly distort time for us.
Just as optical illusions can trick our eyes, auditory illusions can distort our perception of time. 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.
Researchers adapted the one-is-more illusion by swapping the sounds with moments of silence, creating what they dubbed the one-silence-is-more illusion.
During an experiment, nearly 1,000 study participants were immersed in ambient noise (such as that of a restaurant). This noise was interrupted by either a single continuous silence or two discrete silences, and subjects were asked to judge the durations of the silence sequences.
When exposed to the one-silence-is-more illusion, the results were the same as their sound-based counterparts. People thought one long moment of silence was longer than two short moments of silence.
This suggests that people hear silence just like they hear sounds. Other silence illusions, such as silence event-based warping (a pair of tones within a silence event seems further apart in time than a pair of tones in pure silence) and oddball silence, were tested and they all yielded the same outcomes as sound illusions.
"We typically think of our sense of hearing as being concerned with sounds. But silence, whatever it is, is not a sound — it’s the absence of sound," Goh explains. "Surprisingly, what our work suggests is that nothing is also something you can hear."
The One-Silence-Is-More Illusion
The idea wasn’t simply that these silences made people experience illusions, the researchers said. The same illusions that scientists thought could only be triggered with sounds worked just as well when the sounds were replaced by silences.
"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.
The kinds of illusions and effects that seemed to be unique to the auditory processing of a sound are also experienced with silences, suggesting we really do hear absences of sound too.
The findings establish a new way to study the perception of absence, the team said. They plan to keep exploring the extent to which people hear silence, including whether we hear silences that are not preceded by sound.
In the end, the sound of silence may be more than a poetic metaphor. It's a perceptual reality, a new frontier in our understanding of how we interact with the world around us. As you go about your day, take a moment to appreciate the sound of silence. You might be surprised by what you hear.
For the curious, you can experience silence illusions by clicking on the demos on the study's webpage.
The findings appeared in the Proceedings of the National Academy of Sciences.