Let’s try a quick experiment. Look at the two shapes below—one is spiky and jagged, the other is soft and rounded. Now, I’ll tell you that one is named “Bouba” and the other is “Kiki.” Which one is which?
If you’re like over 95% of people, you instinctively assigned “Kiki” to the spiky shape and “Bouba” to the rounded one. This isn’t a coincidence or a lucky guess. It’s a demonstration of the Bouba/Kiki effect, a fascinating window into the hidden connections between our senses and the very fabric of language.
For centuries, the prevailing wisdom in linguistics has been that the relationship between a word’s sound and its meaning is almost entirely arbitrary. But what if that’s not the whole story? What if the sounds of our words carry an inherent, intuitive meaning that our brains are wired to understand? Welcome to the surprising science of sound symbolism.
The Classic Experiment: From “Takete” to “Kiki”
While the “Bouba/Kiki” version is the most famous, this idea began in 1929 with the German-American psychologist Wolfgang Köhler. He presented participants with similar rounded and jagged shapes but used the words “takete” and “maluma.” Just as with Bouba and Kiki, the results were overwhelming: “takete” was the spiky shape, and “maluma” was the curvy one.
In 2001, neuroscientists V.S. Ramachandran and Edward Hubbard revitalized the experiment with the more phonetically distinct words “Bouba” and “Kiki,” finding the same powerful results. The effect holds true regardless of the language you speak or the country you’re from. This isn’t just an English-language quirk; it’s a human one.
The core of the effect lies in the way we produce and perceive the sounds:
- Kiki: To say “Kiki,” your tongue makes a sharp, abrupt movement against the roof of your mouth. The sound is a plosive, a little explosion of air. The vowel /i/ (the “ee” sound) is considered a “sharp” or “thin” vowel. The sound mirrors the visual sharpness of the spiky shape.
- Bouba: To say “Bouba,” you round your lips. The sounds /b/ and /u/ (the “oo” sound) are soft, sonorous, and produced with a rounded, open mouth. The sound mirrors the smooth, gentle curves of the rounded shape.
A Challenge to the Arbitrariness of Language
The Bouba/Kiki effect throws a fascinating wrench into one of the foundational principles of modern linguistics: the arbitrariness of the linguistic sign. This concept, championed by Swiss linguist Ferdinand de Saussure, states that there is no inherent, natural connection between a word (the “signifier”) and the concept it represents (the “signified”).
A dog is called a “dog” in English, “chien” in French, and “inu” (犬) in Japanese. None of these words sound particularly “dog-like.” The connection is purely a matter of social convention. If we all agreed to call dogs “blorps” tomorrow, the word would function just as well.
But Bouba/Kiki suggests that this arbitrariness isn’t absolute. It points to a deeper layer of non-arbitrary connections, a phenomenon known as sound symbolism or phonosemantics. This is the idea that vocal sounds can carry meaning in and of themselves, independent of a learned vocabulary.
It’s Not Just You: Cross-Linguistic and Developmental Evidence
Skeptics might argue that this is just a fluke of certain language families. But study after study has debunked this. The effect has been successfully replicated with speakers of Tamil in India, with communities in rural Namibia, and across dozens of other cultures. It even works on children as young as 2.5 years old, suggesting that this connection is either innate or learned very early, long before our vocabulary is fully formed.
This universality is the most powerful piece of evidence. It implies that the Bouba/Kiki mapping isn’t learned from a specific language but stems from a fundamental aspect of human cognition. Our brains appear to be hardwired to find abstract connections between different sensory inputs.
How Does It Work? A Peek Inside the Brain
So, what’s happening in our heads? Scientists believe the Bouba/Kiki effect is a form of cross-modal mapping, where the brain links information from two different senses—in this case, sight (the shape) and hearing (the word). There are two main theories for how this works.
1. The Motor Mimicry Hypothesis
This is the most intuitive explanation. As mentioned earlier, the physical shape your mouth makes when producing a sound mimics the visual shape. You round your mouth for “Bouba” and make a sharper, more tense shape with your tongue and lips for “Kiki.” Your brain recognizes this congruency between the visual shape of the object and the “motor shape” of your mouth.
2. The Synesthesia Hypothesis
A more abstract theory suggests this is a mild, universal form of synesthesia. Synesthesia is the neurological condition where stimulating one sensory pathway leads to involuntary experiences in a second pathway (e.g., hearing colors or tasting shapes). While most of us don’t have full-blown synesthesia, our brains are still built for it.
The brain might be extracting an abstract property—let’s call it “jaggedness” or “smoothness”—from both the sound and the shape. The sound /k/ is acoustically abrupt and “jagged,” just like the spiky image. The sound /b/ is acoustically smooth and continuous, just like the blobby image. The angular gyrus, a region of the brain known for integrating different types of sensory information, is thought to play a key role in this process of abstract matching.
Sound Symbolism Is Everywhere
Once you start looking for it, you’ll see sound symbolism pop up everywhere in language, far beyond this one experiment.
- Size and Distance: High, front vowels like the /i/ in “little,” “tiny,” “teeny,” or “bit” are often associated with smallness. Deeper, back vowels like the /o/ or /a/ in “large,” “grand,” or “vast” are associated with bigness. Similarly, “here” has a smaller-sounding vowel than the more distant-sounding “there.”
- Onomatopoeia: This is the most obvious example, where words imitate the sounds they describe (“buzz,” “thump,” “hiss,” “splash”). But sound symbolism is subtler and more abstract than simple mimicry.
- Marketing and Branding: Companies instinctively use this. A small, fast car might get a “K” or “T” name, while a luxury lotion brand might favor soft, sonorous sounds like /l/ and /m/. Think about why the nonsense word “Häagen-Dazs” sounds so creamy and decadent—it’s pure sound symbolism at work.
The Music of Language
The Bouba/Kiki effect is more than just a fun party trick. It reveals that language is not a sterile, mathematical system of arbitrary code. It is deeply, fundamentally entangled with our sensory experience of the world.
It shows us that a part of our brain listens not just to the dictionary definition of a word, but to its music—its texture, its shape, its feeling. The link between sound and meaning isn’t always arbitrary. Sometimes, it’s beautiful, intuitive, and profoundly human.
