We hear certain background sounds even when they aren鈥檛 there 鈥� and studying why could help us understand to what extent our perceptual reality is just an illusion.
Josh McDermott and Richard McWalter at the Massachusetts Institute of Technology discovered this illusion while playing around with different sound effects.
You can hear one example in the video below. The audio starts with the sound of applause, which is then overlaid with a loud static sound. You should be able to hear applause in the background.
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This applause isn鈥檛 actually present, however 鈥� when the static cuts in, the applause audio has been completely removed, but our brain assumes that it is still there.
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This effect only works for certain sounds known as 鈥渟ound textures鈥� 鈥� anything that requires lots of different events occurring at the same time. For example, the sound of applause requires lots of people clapping, while the sound of rainfall requires many raindrops hitting a surface.
The illusion works because our brain assumes that all of the events that make up a sound texture will never all suddenly stop at the same time. Our brain focuses on the new louder sound while assuming the initial background sound will continue.
Read more: Sound effects: Five great auditory illusions
But it is also possible to break the illusion, by adding a silent gap before the sound of static. McDermott speculates that this is because our brain understands that there won鈥檛 be any background noises in complete silence, and when the static sound starts up again, there is no reason why the sound texture should start again.
鈥淲e still don鈥檛 know if we鈥檙e born experiencing these illusions, or if perceptual learning is involved,鈥� says McDermott. He says a next step is to do these experiments on young children, to get closer to figuring out how these illusions arise.
Nature Communications
