Scientists find the sound of silence

People register silence in the same way they register sounds, according to new research published in Proceedings of the National Academy of Sciences.

“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,” says lead author Rui Zhe Goh, a graduate student in philosophy and psychology at Johns Hopkins University, US.

“Surprisingly, what our work suggests is that nothing is also something you can hear.”

In the research  1,000 volunteers listened to “auditory illusions” that used silence instead of noise.

“Philosophers have long debated whether silence is something we can literally perceive, but there hasn’t been a scientific study aimed directly at this question,” says co-author Chaz Firestone, an assistant professor of psychological and brain sciences at Johns Hopkins.

Read more: Reducing noise below the sound of silence

“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.”

The researchers asked participants to listen to well-known auditory illusions where sounds had been swapped for silence.

For example, one common auditory illusion is the one-is-more illusion, where people hear a long beep and two short beeps. While both beeping sounds take up the same amount of time, people regularly report the one-beep sound as taking longer.

In this study, the researchers replicated the one-is-more illusion, but they first played background noise, like the sounds of a restaurant, then interrupted it with a long burst of silence or two short bursts.

Credit: Johns Hopkins University

In this, and in other auditory illusions, participants reported the same effects as if they’d heard the sounds.

“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,” says co-author Ian Phillips, a professor of philosophy and psychological and brain sciences also at Johns Hopkins.

“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.”

Next, as well as continuing to investigate hearing silence, the researchers are interested to see if they can produce similar effects with visual disappearances (hello darkness, my old friend…).