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A diagram of the bouba and kiki shapes side by side on a white background

Do people who speak different languages perceive similar correspondences between speech sounds and certain visual properties like shape?

Aleksandra Ćwiek, Leibniz-Zentrum Allgemeine Sprachwissenschaft, Humboldt-Universität zu Berlin.                


Susanne Fuchs, Leibniz-Zentrum Allgemeine Sprachwissenschaft.


Christoph Draxler, Ludwig Maximilian University.

Eva Liina Asu, University of Tartu.

Dan Dediu, Université Lumière Lyon 2.


Katri Hiovain, University of HelsinkiShigeto Kawahara, Keio University.

Sofia Koutalidis, Bielefeld University.

Manfred Krifka, Leibniz-Zentrum Allgemeine Sprachwissenschaft, Humboldt-Universität zu Berlin.

Pärtel Lippus, University of Tartu.

Gary Lupyan, University of Wisconsin-Madison.


Grace E. Oh, Konkuk University.

Jing Paul, Agnes Scott College.

Caterina Petrone, Aix-Marseille Université.

Rachid Ridouane, Sorbonne Nouvelle.

Sabine Reiter, Universidade Federal do Paraná.

Nathalie Schümchen, University of Southern Denmark.

Ádám Szalontai, Hungarian Research Centre for Linguistics.

Özlem Ünal-Logacev, Istanbul Medipol University.

Jochen Zeller, University of KwaZulu-Natal.

Marcus Perlman, University of Birmingham.


Bodo Winter, University of Birmingham.


When presented with a rounded and a spiky shape, and asked which one is the “bouba”, the majority of respondents indicate the rounded shape. When asked which one is the “kiki”, most people indicate the spiky shape. This has come to be known as the bouba/kiki effect. People perceive a correspondence between the spoken words and the visual properties of the shapes, for example, between the rounded lips of articulating the ‘b’ and ‘ou’ in "bouba" and the rounded shape, and between the stop-and-start alternation of articulating the 'k' and 'i' in "kiki" and the spiky shape. First identified by Wolfgang Köhler in his classic 1929 book on Gestalt Psychology (originally with the words “baluba” and “takete”), the bouba/kiki effect has since been the subject of many dozens of psychological studies aiming to understand how and why people are able to recognize correspondences between different perceptual modalities.

Some researchers believe that the bouba/kiki effect may be a clue to the origins of spoken languages. In the absence of words, such perceptual correspondences could have been used by our ancestors to produce meaningful sounds to refer to different things in the world. New words that are perceived to resemble their referent would have been more likely to be understood and adopted by a wider community of speakers. Critical to assessing this hypothesis is determining how universal the bouba/kiki effect is. Rather than reflecting a deeply rooted human capacity to connect sound and vision, the effect could just be a quirk of speaking English. We see similarity between a nonsense word like “bouba” and real words like “balloon”, which just happen to refer to something round. Or maybe the effect results from our writing system: “b” and “o” are rounded letters compared to the spikier “k” and “i”. Indeed, most research on the bouba/kiki effect has been done with literate Westerners, mostly English speakers who write with the Roman alphabet.

To find out how widespread the bouba/kiki effect is across human populations, we – in a collaboration of linguists and psychologists located around the globe – conducted an online test with speakers of 25 languages representing nine language families and ten different writing systems. Our participants included, for example, speakers of Hungarian, Japanese, Farsi, Georgian, and Zulu. The results showed that the majority of participants, independent of their language and writing system, showed the effect, matching “bouba” with the rounded shape and “kiki” with the spiky one. There were some interesting exceptions, though: for instance, Romanian, Turkish, and Mandarin Chinese speakers tended to produce the opposite matching. It remains to determine what drives these cases. One possibility is that these languages contain real words that sound similar to “bouba” and “kiki” but have conflicting meanings. Nevertheless, considering our results altogether, these cases appear to be the exceptions that prove the rule. Our findings suggest that the majority of people across the planet exhibit the bouba/kiki effect, providing the strongest evidence to date that the effect is robust across cultures and writing systems. Our study confirms the possibility that our ancestors could have leveraged correspondences between speech sounds and visual properties like shape in order to create some of the first spoken words. Now, many thousands of years later, the perceived roundness of the English word “balloon” may not be just a coincidence, after all.

 Published in Philosophical Transactions of the Royal Society B, in a special theme issue on 'Voice modulation: from origin and mechanism to social impact'