One of the chicks above is named “Bouba.” The other is named “Kiki.” Going just off of your gut intuition, which one is which?
If you answered that the left chick is “Bouba” and the right chick is “Kiki”, many people agree with you, including speakers of over 25 languages, belonging to 9 language families and 11 writings systems—a surprisingly high number, given that these are purely nonsense words (Ćwiek et al., 2021). For some reason, “bouba” is obviously round, while “kiki” is obviously spiky.
Perhaps even more astonishing is that, as discovered in a recent study by Maria Loconsole and colleagues at the University of Padova, baby chickens are among the population that agrees with you.
What is the bouba-kiki effect?
Most words have an arbitrary relationship to their meaning. Nothing about “cat” inherently refers to the feline domestic animal, and neither does 猫 (māo), बिल्ली (billi), gato, or قطة (qiṭṭa). But certain sounds seem to inherently have meaning.
First described in 1947 by Wolfgang Kölher through the nonsense words “Maluma” and “Takete”, the “bouba-kiki” phenomenon in linguistics refers to this effect (Loconsole et al., 2026). “Maluma” and “bouba” feel inherently round, while “takete” and “kiki” feel inherently sharp and spiky. This effect is common across cultures, languages, and age: even infants as young as 4 months possess this sound mapping, where certain sounds seem to inherently correspond to certain shapes (Ozturk et al., 2013). This effect is even found (to a lesser extent) in blind individuals, though a period of sight seems necessary for the effect to occur (Piller et al., 2023).
The most common explanation for the bouba-kiki effect is the way we say those syllables. When we say “bouba” and similar words, our mouths make a round shape; when we say “kiki” and similar words, our mouths make an angular shape. Our brains thus associate words that are “round” to pronounce with round shapes, and “angular” with angular shapes. Alternatively, the shape of the letters “b” and “o” are round, while the shape of the letters “k” and “i” are angular (Lockwood & Dingemanse, 2015).
However, this hypothesis is challenged by the generic shape hypothesis, which states that humans form generic associations between certain sounds and meanings. This hypothesis was proposed in a study conducted by Ananya Passi and S. P. Arun in 2019, where the bouba-kiki effect was found with unpronounceable words, and an association was even found between clear tones and shape, where higher tones were associated with angular shapes. This indicates that humans potentially form general associations between sounds and shapes, regardless of the way those sounds can be pronounced. However, the reason why those associations might be formed remains unanswered, and these studies have been restricted to humans.
Other animals have been shown to also experience some form of association between sound and another sense: for example, chimpanzees, tortoises, and dogs associate lower pitches with larger objects and higher pitches with smaller objects (Kalan et al., 2014; Korzeniowska et al., 2022; Loconsole et al., 2023). However, the bouba-kiki effect specifically has not been found to exist in other animals, even great apes, such as chimpanzees and a bonobo (Margiotoudi et al., 2019; Margiotoudi et al., 2022).
Baby chicks?
If the effect isn’t even our closest animal relatives, then where else can researchers look? In 2026, Loconsole and her colleagues decided to change tracks and look elsewhere. As surprising as their choice may seem, their pick of animals wasn’t arbitrary: chickens are precocial creatures, which means that they can be tested shortly after hatching, and chicks also share many cognitive mechanisms with human infants (Wood & Wood, 2021).
In the first part of the study conducted by Loconsole and her colleagues, 3-day-old chicks were trained to go around a panel depicting a shape with both spiky and round edges, with food behind the panel acting as an incentive. During the experiment, the chicks were placed in front of two panels. One of the panels displayed a round shape, and the other one displayed a spiky shape, and neither of the panels concealed food. The researchers played a recording of a human voice saying either “bouba” or “kiki” to the enclosure, and they watched to see which panel the chicks would choose.
In the second part of the experiment, 1-day-old chicks were introduced to an enclosure with a screen that once again showed a shape with both spiky and round edges, though there was no incentive. After the chicks grew accustomed to the screen, the researchers changed it up: like the first part of the experiment, the screen now showed two shapes side by side, with one jagged shape and one blobby shape. The researchers once again played either “bouba” or “kiki”, and they recorded which shape the chicks approached first, as well as which shape they spent more time exploring.
The researchers found that the 3-day-old chicks significantly preferred the panel with the round shape when hearing “bouba”, and the panel with the angular shape when hearing “kiki”. They also found the same results with the 1-day-old chicks: when “bouba” was played, the chicks first approached the round shape significantly more and spent more time exploring the round shape. The reverse was true when “kiki” was played.
What does this mean?
The study shows that this bouba-kiki effect is not learned, but rather something inherent that’s present even in the earliest stages of life. One implication of this study is that this crossmodal association, or association between different senses, plays a role in how communication develops between animals. Animals such as chickens do not have language, but they still communicate through various calls and vocalizations. Although these vocalizations aren’t necessarily directly symbolic, having these innate associations may help with future development of more complex communication.
Additionally, the findings of the study indicate that the bouba-kiki effect isn’t specific to humans or even mammals, but rather throughout all vertebrates. But how does this reconcile with past findings wherein the effect was not found in other great apes? After all, it’s rather unlikely that this association evolved separately in birds and in humans, but skipped our closest great ape relatives.
According to Loconsole and colleagues, this difference may be explained by the difference in methodology between experiments, as well as the past experience and training of the research subjects. Kanzi, the bonobo who was tested for the bouba-kiki effect, was already trained in associating sounds and shapes and was capable of correctly matching English words to pictures, which may have played a role in his choices (Loconsole et al., 2026; Margiotoudi et al., 2022).
So what do the findings of the study mean for the bouba-kiki effect and the development of human language? Does this mean that chickens are also capable of speech?
No, not really. The bouba-kiki effect is only one example of the human ability of iconicity, or the capacity to form associations between form and meaning, argue Marcus Perlman and Bodo Winter in their commentary article in response to the 2026 study. In other words, the study reveals that the effect originates further back in the tree of life, but the origins of language lie elsewhere, in a broader framework. The bouba-kiki effect may reflect one way in which human language developed through associations between senses, but humans are able to form much more complex associations in language through a combination of speech, gestures, and visual signs. As such, researchers must look at other, broader areas for more clues in their hunt for the origins of language (Perlman & Winter, 2026).
So overall, the chicks might agree with your naming of their illustrated compatriots, but unfortunately, they won’t be able to say as much in words.
Writing and illustration by Joyce Ma
References
Ćwiek, A., Fuchs, S., Draxler, C., Asu, E. L., Dediu, D., Hiovain, K., Kawahara, S., Koutalidis, S., Krifka, M., Lippus, P., Lupyan, G., Oh, G. E., Paul, J., Petrone, C., Ridouane, R., Reiter, S., Schümchen, N., Szalontai, Á., Ünal-Logacev, Ö., Zeller, J., Perlman, M., Winter, B. (2021). The bouba/kiki effect is robust across cultures and writing systems. Philosophical Transactions of the Royal Society B Biological Sciences, 377(1841), 20200390. https://doi.org/10.1098/rstb.2020.0390
Kalan, A. K., Mundry, R., & Boesch, C. (2015). Wild chimpanzees modify food call structure with respect to tree size for a particular fruit species. Animal Behaviour, 101, 1–9. https://doi.org/10.1016/j.anbehav.2014.12.011
Korzeniowska, A. T., Simner, J., Root-Gutteridge, H., & Reby, D. (2022). High-pitch sounds small for domestic dogs: Abstract crossmodal correspondences between auditory pitch and visual size. Royal Society Open Science, 9(2), 211647. https://doi.org/10.1098/rsos.211647
Lockwood, G., & Dingemanse, M. (2015). Iconicity in the lab: A review of behavioral, developmental, and neuroimaging research into sound-symbolism. Frontiers in Psychology, 6, 1246. https://doi.org/10.3389/fpsyg.2015.01246
Loconsole, M., Benavides-Varela, S., & Regolin, L. (2026). Matching sounds to shapes: Evidence of the bouba-kiki effect in naïve baby chicks. Science, 391(6787), 836–839. https://doi.org/10.1126/science.adq7188
Loconsole, M., Stancher, G., & Versace, E. (2023). Crossmodal association between visual and acoustic cues in a tortoise (Testudo hermanni). Biology Letters, 19(7), 20230265. https://doi.org/10.1098/rsbl.2023.0265
Margiotoudi, K., Allritz, M., Bohn, M., & Pulvermüller, F. (2019). Sound symbolic congruency detection in humans but not in great apes. Scientific Reports, 9(1), 12705. https://doi.org/10.1038/s41598-019-49101-4
Margiotoudi, K., Bohn, M., Schwob, N., Taglialatela, J., Pulvermüller, F., Epping, A., Schweller, K., & Allritz, M. (2022). Bo-NO-bouba-kiki: Picture-word mapping but no spontaneous sound symbolic speech-shape mapping in a language trained bonobo. Proceedings of the Royal Society B Biological Sciences, 289(1968), 20211717. https://doi.org/10.1098/rspb.2021.1717
Ozturk, O., Krehm, M., & Vouloumanos, A. (2012). Sound symbolism in infancy: Evidence for sound–shape cross-modal correspondences in 4-month-olds. Journal of Experimental Child Psychology, 114(2), 173–186. https://doi.org/10.1016/j.jecp.2012.05.004
Passi, A., & Arun, S. P. (2022). The Bouba–Kiki effect is predicted by sound properties but not speech properties. Attention Perception & Psychophysics, 86(3), 976–990. https://doi.org/10.3758/s13414-022-02619-8
Perlman, M., & Winter, B. (2026). In search of meaning. Science, 391(6787), 762–763. https://doi.org/10.1126/science.aee8641
Piller, S., Senna, I., & Ernst, M. O. (2023). Visual experience shapes the Bouba-Kiki effect and the size-weight illusion upon sight restoration from congenital blindness. Scientific Reports, 13(1), 11435. https://doi.org/10.1038/s41598-023-38486-y
Wood, S. M. W., & Wood, J. N. (2021). One-shot object parsing in newborn chicks. Journal of Experimental Psychology General, 150(11), 2408–2420. https://doi.org/10.1037/xge0001043
