The internet loves a great illusion to debate over, and for a while, one of the biggest ones was the infamous picture of a dress, which to some looked black and blue, and to others, white and gold.
But the biggest successor to the great dress debate was the introduction of a short audio clip saying a repeated word over and over - and it drove the internet wild.
The Laurel vs Yanny debate caused endless arguments, and prompted questions about the nature of sound and how our ears and brains work.
This is everything you need to know about how the Laurel vs Yanny illusion tricked our ears.
What was the Laurel vs Yanny illusion?
In May 2018, an audio clip was uploaded to the internet by social media influencer Cloe Feldman which asked listeners to answer a simple question: Do you hear Yanny or Laurel?
The clip featured a computer generated voice which says a repeated word on a loop, which listeners either interpreted as Yanny or Laurel.
The clip proceeded to split the internet in half, with some saying it was obviously saying Yanny, and others convinced that it said Laurel.
How does the illusion work?
Talking to The Guardian, Professor David Alais from The University of Sydney said that the Laurel vs Yanny phenomenon was an example of something called a “perceptually ambiguous stimulus”, such as the face/vase illusion or the Necker cube.
Professor Alais said: “They can be seen two ways, and often the mind flips back and forth between the two interpretations. This happens because the brain can’t decide on a definitive interpretation.
“If there is a little ambiguity, the brain locks onto a single perceptual interpretation. Here, the Yanny/Lauren sound is meant to be ambiguous because each sound has a similar timing and energy content - so in principle, it’s confusable.”
The Professor added: “All of this goes to highlight just how much the brain is an active interpreter of sensory input, and thus that the external world is less objective than we like to believe.”
Speaking to The Verge, Lars Riecke, an assistant professor of audition and cognitive neuroscience at Maastricht University, says that the “secret is frequency”.
Riecke says that the acoustic information that makes some people hear Yanny is a higher frequency than the acoustic information that makes us hear Laurel.
Some of the variation may be down to the audio system playing the audio, but Reicke says that some of it can also come down to the mechanics of our ears.
Reicke explains that older adults tend to start losing their hearing at the higher frequency ranges, which could explain why some people could only hear Laurel and others could only hear Yanny.
It’s a phenomenon that can be mimicked on a computer, Riecke explains - if you remove all the low frequencies, you can hear Yanny, and if you remove the high frequencies, you can hear Laurel.
Bharath Chandrasekaran, a professor in the department of communications sciences and disorders at the University of Texas, also talked to The Verge about the auditory illusion.
Chandrasekaran said that the audio clip is a bit noisy, which could contribute to confusion: “Because it’s noisy, your brain is filling in with what it thinks it should be.”
He also states that when the audio clip was uploaded to the internet, it was accompanied by a visual cue - the message which asks Yanny or Laurel - and this can help shape what people can hear.
What other audio illusions are there?
Another audio illusion which took the internet by storm was the brain storm vs green needle clip.
The video clip featured an old children's toy which made a noise when a button is pressed.
The clip said that if you think about the word brain storm, that’s what you’ll hear, but if you think about the word green needle, you’ll hear that instead.
Another similar illusion is this YouTube video which was posted in 2011, where the repeated word can sound like “Bill”, “pail” or “mayo” depending on what’s happening on the screen.
The mechanics of these two audio illusions are the same as the Laurel vs Yanny clip - noisy audio, visual cues, our brains filling in the gaps and our hearing capabilities can all factor into how one person can hear one thing and another person can hear something totally different.
A version of this article originally appeared on our sister title The Scotsman