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How shapes sound and how sounds shove

by Sam Lemonick
January 12, 2022 | A version of this story appeared in Volume 100, Issue 2


Two syllables, sounds like . . .

A bulbous shape and a spiky shape.
Credit: Philos. Trans. R. Soc., B
Seeing things: People around the world associate the nonsense words bouba with a rounded shape and kiki with a spiky shape.

Can words have textures? As far back as the 1920s, scientists have shown that people associate the sounds of nonsense words with pictures of rounded and spiky shapes. The effect is commonly called the bouba-kiki effect, after the words used in a 2001 study (J. Conscious. Stud. 2001, 8, 3). Participants in that study and subsequent ones tend to match bouba with a drawing of a bulbous shape and kiki with a drawing of a spiky one. In a new study of 25 languages, researchers have shown that the effect is consistent across many languages and cultures (Phil. Trans. R. Soc. B 2021, DOI: 10.1098/rstb.2020.0390).

Aleksandra Ćwiek, a doctoral researcher in phonetics at the Leibniz-Center General Linguistics, says her team found the effect in 17 of the 25 languages tested. Ćwiek, who recorded the words that participants heard, says the results contradict what some previous research suggested: that the effect is associated with the Latin alphabet and connected to the shapes of letters like b and k. The group found the effect largely held even in languages that don’t use Latin letters.

Her group did find some languages in which the bouba-kiki effect isn’t strong, and even examples in which it’s reversed. For instance, Romanian speakers associate bouba with the spiky shape. Ćwiek says one possible explanation is a similar-sounding Romanian word, bubă, which means “wound” and is used especially when talking to young children. “Maybe the connotation of ‘wound’ overrides the round feeling,” she tells Newscripts. Future studies might test that idea by studying more nonsense words.

Ćwiek says that the widespread correspondence between sounds and shapes that the new study reflects may have been important during the beginnings of language development, when shared intuition could have been useful for communicating, but she cautions that those questions are outside her area of expertise.


Lego launcher

Lego minifigure.
Credit: Wikimedia Commons
Sound off: Focused sound waves can bounce Lego minifigures off their feet.

Another word people might associate with spiky shapes is Lego, as anyone who has stepped barefoot on a Lego brick knows. Brian Anderson of Brigham Young University and colleagues are getting a small measure of revenge: they came up with a way to knock over Lego minifigures with focused sound waves.

Anderson described the technique, called “time reversal focused vibrations,” at a recent meeting of the Acoustical Society of America. It works like this: speakers called shakers are connected to a sheet of metal. On the sheet, Anderson’s group arrays Lego minifigures. A sensor positioned beneath a minifigure records the vibrations that travel through the metal when the speakers play, with different sound waves arriving at slightly different times depending on their wavelengths and the shape of the metal sheet. When that recording is reversed and played back through the speakers, the sound waves all arrive at the exact same moment, creating a localized spike of vibrations, which knocks the minifigure off its feet. The technique is accurate and precise enough to topple a single minifigure standing in a Lego crowd of dozens.

The time reversal technique is more commonly used to detect and locate cracks or defects in materials by focusing sound energy at different spots. Anderson first encountered it when he was monitoring the integrity of nuclear waste casks as a researcher at Los Alamos National Laboratory. He developed this Lego-tipping version as a research project for undergraduate students in his BYU group. He tells Newscripts that the minifigures’ light weight and high stiffness make “Lego ideal for thumping.”

The group has made the demonstration into a game, on display at the Swiss Federal Institute of Technology (ETH), Zurich, in which players attempt to knock over one another’s minifigures.

Time reversal techniques aren’t just fun and games for Anderson, however. In addition to continuing his work on materials analysis, Anderson has been exploring ways to use time reversal to focus sound in 3D space so that translations, for instance, could be played for different individuals in the same room without the need for headphones.

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