No quiet place: Scientists say you can hear silence - study

Silence is golden, but is it a sound that people can hear? Yes, according to a graduate student in philosophy and psychology in interdisciplinary humanistic studies at the famed Johns Hopkins University in Baltimore. Lead author Rui Zhe Goh used auditory illusions to reveal how moments of silence distort people’s perception of time and addressed the debate of whether people can hear more than sounds, a problem that has puzzled philosophers for centuries.

“We typically think of our sense of hearing as being concerned with sounds. Silence, whatever it is, is not a sound – it’s the absence of sound,” he said, “but surprisingly, what our work suggests is that nothing is also something you can hear.” Do we hear only sounds or can we also hear silence? These questions are the subject of a centuries-old philosophical debate between two camps – the perceptual view (that we literally hear silence), and the cognitive view (we can only judge or infer silence).

The team members have published their research in the Proceedings of the National Academy of Sciences under the title “The perception of silence.”

Hearing nothing: Understanding the sound of silence

“Here, we take an empirical approach to resolve this theoretical controversy. We show that silences can ‘substitute’ for sounds in event-based auditory illusions,” they wrote. “Seven experiments introduce three ‘silence illusions’ adapted from perceptual illusions previously thought to arise only with sounds. In all cases, silences elicited temporal distortions perfectly analogous to their sound-based counterparts, suggesting that auditory processing treats moments of silence the way it treats sounds. Silence is truly perceived, not merely inferred.”

Auditory perception is traditionally conceived as the perception of sounds – a friend’s voice, a clap of thunder or a minor chord, they continued. “But daily life also seems to present us with experiences characterized by the absence of sound – a moment of silence, a gap between thunderclaps or the hush after a musical performance. In these cases, do we positively hear silence? Or do we just fail to hear and merely judge or infer that it is silent?”

THIS LONGSTANDING question remains controversial in both the philosophy and science of perception, with prominent theories holding that sounds are the only objects of auditory experience and thus that our encounter with silence is cognitive, not perceptual. But this debate has largely remained theoretical and without a key empirical test.

“Here, we introduce an empirical approach to this theoretical dispute, presenting experimental evidence that silence can be genuinely perceived and not just cognitively inferred. We ask whether silences can ‘substitute’ for sounds in event-based auditory illusions empirical signatures of auditory event representation in which auditory events distort perceived duration.”

In tests of 1,000 participants, the team swapped the sounds in the one-is-more illusion with moments of silence, re-working the auditory illusion into what they dubbed the one-silence-is-more illusion. 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.

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. 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.

They conducted seven experiments to introduce three “silence illusions” – the one-silence-is-more illusion, silence-based warping and the oddball-silence illusion, each adapted from a prominent perceptual illusion previously thought to arise only from sounds. Subjects were immersed in ambient noise interrupted by silences structurally identical to the sounds in the original illusions. In all cases, silences elicited temporal distortions perfectly analogous to the illusions produced by sounds.

Participants were asked to listen to soundscapes that simulated the noise in 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 wasn’t simply that these silences made people experience illusions, the researchers said. It was that the same illusions that scientists thought could only be triggered with sounds worked just as well when the sounds were replaced by silences.

“Our results suggest that silence is truly heard, not merely inferred, introducing a [new way and] general approach for studying the perception of absence,” they concluded.