Absence of sound: Scientists find silence can be heard

People may hear silence in the same way that they hear sounds, study suggests

A sound-healing experience, which is a holistic approach to healing and a form of therapy for relaxation, at Manarat, Abu Dhabi. Khushnum Bhandari / The National

Althought it might not be deafening, scientists have discovered that silence can be heard after all.

Using auditory illusions, researchers found how moments of silence distort people’s perception of time.

Solving a mystery over which philosophers have puzzled for centuries, the findings address the debate of whether people can hear more than sounds, including silence.

“We typically think of our sense of hearing as being concerned with sounds," said lead author Rui Zhe Goh, a Johns Hopkins University graduate student in philosophy and psychology.

“But silence, whatever it is, is not a sound – it’s the absence of sound.

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

In auditory illusions, the brain thinks it can hear something that is either not there or exists in a different form to how it is perceived.

Like optical illusions that trick what people see, auditory illusions can make people hear periods of time as being longer or shorter than they actually are.

A mass meditation on Day 2 of the Glastonbury festival in Pilton, Somerset, south-west England, on June 22. AFP

One example is known as 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 almost 1,000 people, the researchers swapped the sounds in the one-is-more illusion with moments of silence.

They found the same results – people thought one long moment of silence was longer than two short moments of silence.

Other silence illusions yielded the same outcomes as sound illusions, the study found.

In the study, researchers adapted well-known auditory illusions to create versions in which the sounds of the original illusions were replaced by moments of silence.

For example, one illusion made a sound seem much longer than it really was.

In the team’s new silence-based illusion, an equivalent moment of silence also seemed longer than it was.

According to the research, these silence-based illusions produced the same results as the sound-based ones, suggesting people hear silence just as they hear sounds.

“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," said Chaz Firestone, an assistant professor in the US who directs the Johns Hopkins Perception and Mind Laboratory.

“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.”

People in the study were asked to listen to soundscapes that simulated the din of busy restaurants, markets and train stations.

They then listened for periods within those audio tracks when all sound stopped abruptly, creating brief silences.

The idea was not simply that these silences made people experience illusions, it was that the same illusions scientists thought could only be caused by 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 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.”

The researchers say the findings, published in Proceedings of the National Academy of Sciences, establish a new way to study the perception of absence.