Bouba and kiki: the cross-cultural sound that everyone agrees is spiky

Wolfgang Köhler ran the experiment first in 1929 on Tenerife. He showed two abstract shapes — a rounded amoeba-like blob and a spiky star-like figure — to local speakers. He asked which was takete and which was maluma. Almost everyone gave the same answer: maluma for the round one, takete for the spiky one.

Vilayanur Ramachandran and Edward Hubbard updated the experiment in 2001 with bouba and kiki. Same result. Across English, Tamil, and several other languages, roughly 95% of subjects called the rounded shape "bouba" and the spiky one "kiki" (Ramachandran & Hubbard, 2001).

The phenomenon — sound symbolism — is one of the more striking findings in cognitive science. It contradicts a foundational assumption of linguistics.

1. The mapping isn't arbitrary

Ferdinand de Saussure's 1916 Course in General Linguistics established a foundational principle: the relationship between a word and its meaning is arbitrary. There's no reason "tree" should refer to a tree; it's a cultural convention. This principle anchored modern linguistics.

Sound symbolism challenges that principle. The bouba/kiki finding shows that at least some sound-meaning relationships are not arbitrary — they map consistently across humans regardless of which language the human speaks.

2. The replication record

The basic finding has replicated across:

• Speakers of dozens of languages, including unrelated language families
• Pre-literate children (suggesting the mapping doesn't require literacy)
• Pre-verbal infants (4-month-olds look longer at shape-sound matches than mismatches, per Maurer et al. 2006)
• Speakers of languages where neither "bouba" nor "kiki" exists as a meaningful word

Maurer's developmental work was particularly important. Infants showing the effect before they can speak indicates the mapping is built in, not learned (Maurer, Pathman, & Mondloch, 2006).

3. The proposed mechanism

Several mechanisms have been proposed, and they're probably all partially correct:

Articulatory grounding. Saying "bouba" requires rounded lips and an open jaw; saying "kiki" requires tense lips and a sharp tongue articulation. The mouth shapes resemble the visual shapes. Cross-modal neural connections may link them.

Acoustic grounding. "Bouba" contains lower-frequency, smoother sound waves. "Kiki" contains higher-frequency, sharper transitions. Visual roundness and acoustic smoothness may share an underlying brain mapping.

Multisensory neurons. Some sensory neurons respond to both vision and audition. The cross-modal connections in synesthesia (see separate piece) may exist in milder form in everyone.

4. The implications

For linguistics: sound symbolism is now recognized as a partial exception to the arbitrariness principle. Languages do have some non-arbitrary sound-meaning correspondences. The ideophones — words that sound like what they mean — that exist in many languages (English "splash," "buzz," Japanese "kira-kira" for sparkling) reflect this.

For language learning: when learning vocabulary, exploiting cross-cultural sound symbolism may aid memory. Words whose sounds align with their meanings are easier to learn and retain than arbitrarily-mapped ones (Imai et al., 2008).

For evolution of language: sound symbolism may have been a building block of early language. The first vocabulary items could have been somewhat iconic, with arbitrary words developing later. This is contested but consistent with several lines of evidence.

5. The takeaway

The bouba/kiki effect is small. The vocabulary of most languages is overwhelmingly arbitrary. But the existence of consistent cross-cultural sound-meaning mappings tells us something important: human minds carry shared cross-modal connections that predate any specific language.

This is one of the more elegant findings in cognitive science. A trivial-seeming experiment — naming two shapes with nonsense syllables — reveals deep structure in how the mind organizes sensory information.