Do you hear the same things as me? Probably not. As these weird audio illusions show, people have radically different opinions about what reaches their ears, says David Robson.

“You know you were told to be nice and not to heckle?” Sophie Meekings asks her audience in the dingy cellar of the North London pub. “Well, you can heckle me if you want – it’s just there’s not much point, because I won’t be able to hear you.”

She’s only partly joking. Meekings is profoundly deaf and would struggle to make out the conversations around her. The subject of her talk is, in fact, hearing – and the strange tricks our ears can play on the mind.

To explore the theme, she plays some auditory illusions, which are among the strangest sounds I have ever heard. What strikes me is just how easily the eerie and futuristic sounds divide the audience. Like the viral furore #TheDress, which prompted radically different interpretations of colour, the audio clips she played – and others like them – challenge our assumptions about how we each perceive the world.

We’re often told that seeing isn’t believing, but I had never realised just how fragile and deceptive our hearing can be, too. Once I have left the pub’s cellar and made my way to the hustle and bustle of King’s Cross Station, I begin to wonder just how much of what I hear is created by my brain. My soundscape will never be quite the same way again.

Curious to know more, I meet Meekings in her lab at University College London two weeks later, and she explains a bit more about her talk and her career. Despite encouragement from teachers and lecturers – who wrongly assumed that she would naturally be fascinated by her disability – she was initially rather reluctant to pursue auditory neuroscience. Eventually, however, a more tactful member of staff managed to articulate why she might find the subject fruitful. “He flattered me and said you might have a new and novel experience on how people hear things,” she says. “And I thought well yes, I might.”

Today, her research mostly lies in understanding the way we deal with noise during a lively party, say. It turns out that even when we are absorbed in conversation, our brains are simultaneously monitoring background chit-chat to help precisely time our speech to fall at the quietest moments. She’s currently conducting brain scans to find out how we do that extra work, without it leaving us tongue tied and confused.

This interest in unpicking how the brain processes complex sounds was also how she ended up talking about auditory illusions at the Science Showoff event – an open mic comedy night for scientists. “People aren’t really aware that the sound that I hear may not be the same as the sound that you hear,” she says.

Meekings’ first example, the “tritone paradox”, may seem deceptively simple, but it demonstrates the principle beautifully. You can hear it for yourself, below.

The tritone paradox

You can hear four pairs of notes. Within each pair, is the second note higher or lower? Playing the track in the dark cellar of the North London pub, Meekings asked us to raise our hands if we hear the pitches rising, or falling. The audience was divided 50:50. Musicians, in particular, were adamant that they knew which way the pitches were moving. And, like the reactions to “the dress”, it was deeply disconcerting to find that the person next to you was not hearing the same thing. “It’s troubling, because we want to feel that we all have the same experience of the world,” says Meekings.

In reality, there’s no right answer. Each note is a composite of many different computer-generated tones, separated by an octave, so it’s impossible to say if the one that follows is above or below on the musical scale.

The brain hates to be uncertain, though – so it makes a convincing guess. Strangely, according to research by Diana Deutsch at the University of California San Diego, our response probably depends on our accent or language: Californians tend to come to the opposite conclusions of people from England, for instance. For this reason, she thinks that the speech patterns of our childhood might somehow shape the way the brain maps musical notes. (Along these lines, Deutsch has also found that repeated words can start to sound like singing, perhaps evoking an ancient link between music and language.)

The same computer-generated, ambiguous tones help create the next, ear-splitting sound:

The rising tone illusion

What do you hear? Many people hear the tone continuously rising and rising. In fact, it’s going in cycles – a new rising tone starts as the previous one ends.

In some ways, it is similar to the spinning barbershop pole, whose stripes seem to be forever slinking towards the heavens – these are the aural and visual equivalents of perpetual motion. Christopher Nolan used the same trick in The Dark Knight, creating the sensation that the rev of the Batpod’s engine is constantly accelerating. The illusion also works with descending scales, creating an oddly deflating effect:

During our conversation, Meekings points me to Deutsch’s website, which is a goldmine of other, mind-bending sounds that divide people. Consider this one, for example:

The phantom word illusion

What did you hear? To me, it sounds obvious that a female voice is repeating “no way” to oblivion. But other listeners have variously reported window, welcome, love me, run away, no brain, rainbow, raincoat, bueno, nombre, when oh when, mango, window pane, Broadway, Reno, melting, or Rogaine.

This illustrates the way that our expectations shape our perception, says Deutsch. We are expecting to hear words, and so our mind morphs the ambiguous input into something more recognisable. The power of expectation might also underlie those embarrassing situations where you mishear a mumbled comment, or even explain the spirit voices that sometimes leap out of the static on ghost hunting programmes.

Or consider this similarly divisive sound:

The scale illusion

Deutsch has found that right-handers tend to hear the higher tones in their right ear, while left-handers often hear them in the left – or in both ears at the same time. It is a striking example of the way small, individual differences in brain structure can radically alter our perception, while we are completely oblivious to the fact that our sense is profoundly different to the person next to us.

These errors are the exceptions that prove the rule: the brain’s capacity to mould and refine our senses normally helps us make sense of the world, so we can hear “stop” above the roar of traffic, for instance. Meekings compares this auditory mess to a bowl of spaghetti; somehow, the brain can unravel each and every strand of sound. “You’re basically an auditory detective every day because you get all this ambiguous info, like sound spaghetti, and you do it so well you don’t know you’re even doing it,” she says.  

Without that filtering, Meekings herself would not be able to use lip-reading to boost the inputs from her hearing aid. She is in constant awe of that process. “My research has made me have more respect for my own ears – because given the input that I get, my brain is amazing at resolving it into something that makes sense,” she adds.

The illusions, she thinks, can give us all a bit more appreciation of those wonders. “It’s only when you hear these strange things that you suddenly realise you are doing something really complicated, really fragile.”

Audio clips courtesy of Diana Deutsch, whose CDs of auditory illusions can be found at Philomel Records. (Audio clip images: Alamy)

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Update: An earlier version of this article contained a youtube video with inappropriate imagery. We regret the error, and thank one of our Twitter followers for spotting this.

In the phantom word illusion, people hear everything from ‘rainbow’ to ‘mango’