Auditory illusions: new research discovers how our ears play tricks on us
- Written by The Conversation
Inspired by owls and their amazing ability to find their prey by hearing alone, my team decided to test how good humans are at discerning sounds.
We were surprised to find just how bad we are. As our research shows, our hearing is fooled in dramatic ways.
Our experiment was simple. We tapped two metal spoons together in different positions around a blindfolded person.
It was easy for them to distinguish between sounds coming from the left or right, but when we clapped the spoons directly in front of them, they almost always heard the sound as coming from behind them.
You can try this yourself – it makes for a great trick for your next dinner party. All you need is two spoons and a blindfold. You need to ask the participants to keep their head still and you should avoid giving away where you are.
When you click the spoons in front of their face or down near their lap, they will typically hear it behind them. It can be incredibly compelling: participants often heard the sound behind them even when they knew it was in front of them.
We have repeated this in many environments – in a lab, an office, a lecture theatre, a soundproof room and even out on a rural lawn. We also tested participants while standing or sitting down and we tried different kinds of sounds, including pure tones, explosions and a ringing bell.
The result was always the same. We have now also confirmed this under controlled laboratory conditions where a computer selects locations at random and a researcher taps the spoons there.
With only two ears to rely on, our hearing infers direction from subtle timing and intensity cues. But these cues can be misleading. They will be similar for sounds directly in front and behind us.
However, this only means we should be bad at telling where the sound is, known as “front-back confusion”.
It does not explain why we hear the sound so convincingly behind us.
One reason for the illusion could be that the sounds we used are very brief. Many sounds in the real world last longer. Moving your head – and with it your ears – would break the illusion because each ear would hear the sound differently.
Perhaps that is why we rarely notice this illusion in everyday situations.
Our discovery highlights a limitation in how we interpret the soundscape around us. Understanding this better will help us figure out how our brain works.
Does our hearing rely on expectations about where sounds “should” come from? Perhaps our hearing prefers locations outside our field of view when we can’t see anything. We want to test this possibility in future research.
We can test how the illusion changes after people have worn a blindfold for a longer time. We also want to find out whether blind people or those with low vision experience this illusion.
This last point is important. Hearing where things are in the world matters for all of us – such as when crossing the road. But those with impaired vision must rely on their hearing.
People who lost their sight only recently could be especially at risk. A better understanding of why we mishear sounds could help avoid dangerous confusions.
