The question is seemingly a straightforward one: Do you hear Yanny or Laurel?
Yet the answer for the millions of people who have listened to the short clip since it appeared on Twitter on Monday is proving as divisive as the infamous gold and white dress debate of 2015.
The seconds-long soundbite has provoked intense discussion on social media as well as in offices and living rooms across continents, as people adamantly insist that their version is indeed what the synthetic voice is saying.
Academics have also offered a number of explanations for the baffling phenomenon. Theories range from the way our hearing changes as we age, to people’s brains being primed by seeing the written word first, to accent variation between British and American listeners influencing what they pick up.
RolandCamry, who wished to remain anonymous, told the Telegraph that after hitting the website's audio pronunciation function to hear how the word should sound his sister told him she heard it as “Yanny”.
To settle the debate he posted the audio clip on a Reddit forum, posing the simple question: “What do you guys hear?”
The comments soon blew up with posters arguing about whether it was saying Yanny or Laurel. One commented: “I hear Laurel and everyone is a liar”.
What do you hear?! Yanny or Laurel pic.twitter.com/jvHhCbMc8I— Cloe Feldman (@CloeCouture) May 15, 2018
The clip then went viral when it was tweeted on Tuesday by YouTuber Cloe Feldman and has since been listened to more than five million times.
The conundrum has also been vexing celebrities such as talk show host Ellen DeGeneres and American model Chrissy Teigen, who have both weighed in with their thoughts.
Literally everything at my show just stopped to see if people hear Laurel or Yanny. I hear Laurel. https://t.co/efWRw1Gj0L— Ellen DeGeneres (@TheEllenShow) May 15, 2018
it's so clearly laurel. I can't even figure out how one would hear yanny.— christine teigen (@chrissyteigen) May 15, 2018
Neuroscientist Dr Hannah Critchlow of Cambridge University, whose new book Consciousness discusses how the brain alters perception, said a number of factors could influence what people hear, including recent experiences.
She said: "The brain is trying to make sense of the world all the time, and everyone has a unique perception on what is going on around them, and what they see and hear.
"I have just been sent flowers for my birthday, and I hear 'laurel', so that could be because my mind is focused on those flowers. Younger people can also hear higher frequencies so there could be something in that too. There are probably several things going on here."
An 'ambiguous figure'
Scientists say it highlights the difference between hearing and listening, where hearing happens in the ear, but listening occurs in the brain, where meaning is attributed to sound.
Scientifically, the clip is not actually an illusion at all, but rather an "ambiguous figure", or bistable precept, in which the mind is forced to choose between two different states.
It is the auditory equivalent of Joseph Jastrow’s well known rabbit/duck illustration, or Rubin's vase, where the brain interprets either two vases or two faces.
In the word "laurel", the noises made by the throat and mouth to produce the sound are at two different frequencies, creating the ambiguity. For example, a high frequency is needed for the "l" but a low frequency is required for "r".
A spectrogram of the clip shows that both the sounds "laurel" and "yanny" are present, but at different ends of the sound spectrum.
Likewise, because the original audio clip is slightly muffled it leaves room for individual interpretation.
The way people make sense of sound is influenced by what they hear regularly, so people who have closer friends called "Danny" or "Annie" would be more likely to pick up the sound "yanny".
Trevor Cox, professor of acoustic engineering at the University of Salford said: “If you look at the spectrogram you can see both sounds are there, on top of each other.
“So the sound that an individual picks up could be based on sounds they hear often, or how words are pronounced in their language or dialect. Or maybe you’ve got a friend called Laurel, so you are more attuned to hearing that word.
“Also if you have noise-induced hearing loss you will struggle to hear sounds in the middle of that range so would only be able to hear 'laurel'. So if you struggle to hear ‘yanny’ maybe you are getting into that region of hearing loss.”
One factor that could be affecting what people hear is age as our ears become less adept at picking up higher frequencies as we get older.
Young people find higher frequencies easier to hear, while people suffering age-related hearing loss start to lose the ability to hear sounds around 4,000HZ, exactly the frequency of the "yanny" noise.
So if you can’t hear "yanny", it could be a sign of increasing years or even hearing damage.
Lauren Laverne, the radio broadcaster , tweeted that she was hearing "laurel" whereas her seven-year-old daughter was hearing "Yanny".
Laurel for me (no surprise after 20 years in DJ headphones) Yanny for the 7 year old https://t.co/DX23SscQhm— Lauren Laverne (@laurenlaverne) May 16, 2018
Charles Spence, professor of experimental psychology at Oxford, said he could only hear "laurel" and that could be because of his age
He said: "If there was stuff going on at high frequency range maybe you would get young people hearing/and being influenced by that, but not oldies?"
Jane Setter, a professor of phonetics at the University of Reading, said people may also be hearing different names depending on where they live.
“There may well be differences between British and American listeners,” she told the Telegraph.
“The phenomenon seems to have started off with American listeners’ perceptions of a recording of 'Laurel' generated by computer ie synthesized.
“Accent differences will predispose the brain to hearing certain patterns so it would be interesting to see if a Brit, Aussie, American pattern emerges – but I’m not sure who’s collecting that data, and it will be difficult to do so now with any research rigour.”
Another factor that could influence what name listeners hear according to Prof Setter was seeing the written word first in the tweet.
As English speakers read from left to right this could prime the brain to expect to hear “yanny” for some people.
Alex Holcombe, a cognitive psychologist at the University of Sydney, has also explained that the audio quality of the clip could be an influence as our brains effectively fill in the blanks when presented with low sound quality.
you can hear both when you adjust the bass levels: pic.twitter.com/22boppUJS1— Earth Vessel Quotes (@earthvessquotes) May 15, 2018
He said: “Because our brains are almost every day trying to understand what was said under less than ideal (noisy) conditions, it is in the habit of making strong guesses from ambiguous stimuli.
“If the auditory signal is somewhere between the prototypical way of saying ‘laurel’ and ‘yanny’, then the brain may tend to force it towards one or the other, as it does with the phonemic restoration effect.”