'Laurel or yanny' - clip leaves millions bewildered
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 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 with the rest 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," said Charles Spence, professor of experimental psychology at Oxford University. 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 they see and hear.
"I have just been sent flowers 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."
Scientifically, it is not an illusion at all, but rather an "ambiguous figure", in which the mind is forced to choose between two different states.
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.