Answer to a baffling audio post is all in the mind’s ear
Not since the dress colour illusion have we called into question our own sanity and judgment to such a degree. A simple audio entry for “laurel” on Vocabulary.com left millions bewildered this week because half of listeners insisted they could only hear the sound “yanny”.
The global bafflement was similar to that sparked by the Roman Originals dress posted on Twitter in 2015, which many swore was white and gold but the rest were sure it was black and blue.
But, unlike the dress illusion, scientists say the four-second audio clip may reveal far more about how people perceive the world than they realise.
It might even signal a generational divide.
“Stuff going on at a high-frequency range you would get young people hearing, and being influenced by that, but not oldies,” Charles Spence, professor of experimental psychology at Oxford University, said.
Dr Hannah Critchlow, a neuroscientist from Cambridge University, said: “The brain is trying to make sense of the world all the time and everyone has a unique perception of 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’ 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.”
Scientifically, it is not actually an illusion at all, but rather an “ambiguous figure”, 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.
A high frequency is needed for “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.
Young people find higher frequencies easier to hear, while people suffering age-related hearing loss start to lose the ability to hear sounds around 4000HZ, exactly the frequency of the “laurel” noise.
So if you can’t hear “laurel”, it could be a sign of increasing years or even damaged hearing.
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 friends called Danny or Annie would likely pick up “yanny”.
Trevor Cox, professor of acoustic engineering at Salford University, 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.
“Also if you have noise-induced hearing loss, you will struggle to hear sounds in the middle of that range, so would only hear ‘laurel’. So if you struggle to hear ‘yanny’, maybe you are getting into that region of hearing loss.”