Hear the word “circle,” and you’ll probably think of something round. Hear “razor,” and you’ll think of something sharp. But what about a seemingly nonsense word such as “kiki” or “bouba”?
In a famous linguistics study, researchers showed these words make English speakers think of blobby and sharp shapes, respectively. Now, the most extensive study of this finding yet—testing 917 speakers of 25 languages that use 10 different writing systems—has found that 72% of participants across languages associate the word “bouba” with a blobby shape and “kiki” with a sharp one.
Such “cross-sensory” links—here, between speech and vision—show people can use nonsense words and other vocal noises to evoke concepts without using actual language. That could help explain how language evolved in the first place, says Aleksandra Ćwiek, a linguistics Ph.D. student at the Leibniz-Centre General Linguistics who led the new study.
“It’s exciting to see more work on this phenomenon with a greater diversity of languages,” says Lauren Gawne, a linguist at La Trobe University who was not involved with the study. Testing speakers from different writing systems is especially useful, she says, because it helps figure out exactly what underlies the finding.
Past research has pointed to the spikiness of the letter K, and roundness of the letter B, as the primary reason for the effect of “kiki” and “bouba” on English speakers. But other work has found that children who haven’t yet learned to read also make the association, as do Himba people in Namibia, who have limited contact with Westerners and don’t use written language.
To understand how much of a role writing plays in the finding, Ćwiek and her colleagues wanted to test speakers from a much wider sample of languages—and, crucially, different writing systems. She and colleagues were already running a large international experiment across multiple countries, and they realized they could easily add on the short bouba-kiki test at the end of the task. They included speakers of languages from around the world—from Albanian to isiZulu in South Africa—and writing systems as different as Thai, Georgian, and Korean. The researchers recorded Ćwiek saying the two words aloud, and asked participants to choose whether a pointy, starlike shape or a blobby, cloudlike shape best matched each recording.
The volunteers overwhelmingly matched “bouba” with the round shape and “kiki” with the spiky one, the authors report today in the Philosophical Transactions of the Royal Society B. The finding suggests people make a genuine link between the sounds and the shape. It also adds to a growing pile of evidence that challenges an old linguistic dogma: the belief that the sounds that make up a word have no relationship to its meaning.
But there were important differences across languages. Whereas 75% of speakers whose languages use the Roman alphabet—including English and other European languages—made the link, only 63% of speakers of other languages such as Georgian and Japanese did. And three languages—Romanian, Turkish, and Mandarin Chinese—didn’t show the effect at all.
There are good reasons why the finding might look different across languages, says Suzy Styles, a linguist at Nanyang Technological University.
Different languages have their own rules for what sounds and syllables can fit together; in English, for example, you can’t start a word with the sound “ng,” although this is perfectly fine in isiZulu. When the test words in an experiment don’t match these rules, speakers don’t have strong cross-sensory associations, Styles says: “An English speaker finds it hard to decide whether ‘srpski’ is spiky or round, because it doesn’t sound ‘wordy’ in our language.”
It could also be that the made-up words have real meanings in certain languages, Ćwiek says. Buba is a Romanian word used for a small child’s wound—like “ouchy”—which could feel more like a “spiky” association for Romanian speakers, she says. And cici, pronounced “gee-gee,” means “cute” in Turkish. That could give “kiki” associations with round-headed, chubby babies, Ćwiek adds.
Some evolutionary linguists have suggested language may have started not with speech, but with gesture, because it’s so much easier to illustrate an idea with hands—like miming the shape of a tree, Ćwiek says. But that explanation just raises a new question: Why did speech emerge at all? The growing evidence that vocal noises can also evoke ideas like shape or size helps close that gap, she says, hinting that both gesture and speech “have played a significant role at the very core of language.”
The study is robust, and its control of writing systems is “useful and important,” says Mark Dingemanse, a linguist at Radboud University. But linguists also need to better understand how cross-sensory associations like these play a role in real-world languages, he says: “For that, we need to move beyond bouba and kiki.”