For a long time, philosophers have pondered the nature of what we hear and by association, the nature of the perception of silence. Do we only hear sounds? Some might argue that we hear sounds and their sources — a singer and her voice. However, experience leads us to believe that we also hear silence, the absence of sound, for example, when a dramatic piece of music comes to an end.
The view that we only hear sounds centers on the idea that perception is only ever of positive things and that we are incapable of perceiving negative phenomena or the lack of something. If this is the case, then silence is not something we hear — it is just the absence of sound. While this debate has largely remained theoretical, a new study has lent support to the intuition that silence is something we actively hear.
What Is the Sound of Silence?
Two main perspectives have tried to describe the nature of the perception of silence, and therefore provide an account of sound. The cognitive view would suggest we don’t, strictly speaking, hear silence. Instead, we judge or infer from the absence of auditory input that it must be silent, and so we experience a lack of sound. According to the perceptual view, however, we literally hear silence. Experiencing silence is not a failure to hear; the experience of silence is an active perceptual task.
Ian Phillips, professor of philosophy and brain science at Johns Hopkins University, and his co-authors devised a neat way of testing whether our brains treat the absence of sound in the same way as we treat actual sound, and they did this by harnessing a known auditory illusion.
“We reasoned that if we found exactly the same kinds of illusions with silences substituted for sounds, this would be evidence that our auditory systems are treating silences in the same way they are treating sounds. And that would be evidence we do literally hear silences,” says Phillips.
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Does Silence Have a Sound?
The specific illusion the researchers harnessed arises through the way our auditory systems carve up continuous sound waves which interact with our eardrums into discrete, punctuated events — a process called event segmentation.
“In our illusions, this process of event segmentation leads to distortions of duration. For example, in the so-called "one-is-more illusion" (created by Sami Yousif and Brian Scholl at Yale) a single long tone sounds longer than two shorter tones with a brief gap in between, even though the total durations of the two sequences are the same,” says Phillips.
“As we predicted, we found that the same illusions occurred in the same way when silences were substituted for sounds. This suggests that auditory processing treats moments of silence the way it treats sounds. And in turn that is evidence that we really do hear silences,” he adds.
Phillips and his co-authors' work has some pretty interesting philosophical implications for how we should think about perception. Since it provides evidence that we perceive at least one kind of absence — silence — it may also point to the perception of other kinds of absence in other sensory modalities like vision and touch.
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How We Experience Silence
Some thinkers have taken the idea that perception is only ever of positive things as a way of distinguishing perceiving from thinking and believing. However, this new research challenges this claim.
“To take another example, sometimes people have insisted that we can only ever perceive things which causally impact us in some way. But can silences — absences of sounds — have a causal impact on us? That's not obvious. So if we can hear silences, a simple picture about causation and perception needs rethinking,” adds Phillips.
One popular contemporary account of perception, namely predictive processing, where perceptual experiences are a matter of top-down active construction and where sensations serve as error correction mechanisms, shouldn't find anything too problematic with these results. Although, Phillip and his colleagues are not committed to this view of perception in general.
“If our auditory experience of sounds is a matter of top-down active construction, as the predictive processing theorist claims, then our results suggest that our experience of silences is too,” says Phillips.
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