The bouba/kiki effect is a non-arbitrary mapping between speech sounds and the visual shape of objects. This effect was first observed by German-American psychologist Wolfgang Köhler in 1929. In psychological experiments first conducted on the island of Tenerife (where the primary language is Spanish), Köhler showed forms similar to those shown at the right and asked participants which shape was called "takete" and which was called "baluba" ("maluma" in the 1947 version). Although not explicitly stated, Köhler implies that there was a strong preference to pair the jagged shape with "takete" and the rounded shape with "baluba".
In 2001, Vilayanur S. Ramachandran and Edward Hubbard repeated Köhler's experiment using the words "kiki" and "bouba" and asked American college undergraduates and Tamil speakers in India "Which of these shapes is bouba and which is kiki?" In both groups, 95% to 98% selected the curvy shape as "bouba" and the jagged one as "kiki", suggesting that the human brain somehow attaches abstract meanings to the shapes and sounds in a consistent way. Work by Daphne Maurer and colleagues shows that even children as young as 21⁄2 years old may show this effect as well. The effect does not occur in all communities, and it appears that the effect breaks if the sounds do not make licit words in the language.
The effect has also been shown to emerge when the words to be paired are existing first names, suggesting that some familiarity with the linguistic stimuli does not eliminate the effect. A study showed that individuals will pair names such as "Molly" with round silhouettes, and names such as "Kate" with sharp silhouettes. Moreover, individuals will associate different personality traits with either group of names (e.g., easygoingness with "round names"; determination with "sharp names"). This may hint at a role of abstract concepts in the effect.
Ramachandran and Hubbard suggest that the kiki/bouba effect has implications for the evolution of language, because it suggests that the naming of objects is not completely arbitrary.:17 The rounded shape may most commonly be named "bouba" because the mouth makes a more rounded shape to produce that sound while a more taut, angular mouth shape is needed to make the sounds in "kiki". Alternatively, the distinction may be between coronal or dorsal consonants like /k/ and labial consonants like /b/. Additionally, it was shown that it is not only different consonants (e.g., voiceless versus voiced) and different vowel qualities (e.g., /a/ versus /i/) that play a role in the effect, but also vowel quantity (long versus short vowels). In one study, participants rated words containing long vowels to refer to longer objects and short vowels to short objects. The presence of these "synesthesia-like mappings" suggest that this effect might be the neurological basis for sound symbolism, in which sounds are non-arbitrarily mapped to objects and events in the world. In 2019, researchers published the first study using fMRI to explore the bouba/kiki effect. They found that prefrontal activation is stronger to mismatching (bouba with spiky shape) than to matching (bouba with round shape) stimuli. Interestingly, they also found that sound-shape matching also influences activations in the auditory and visual cortices, suggesting an effect of matching at an early stage in sensory processing.
More recently, research indicated that the effect may be a case of ideasthesia. Ideasthesia (alternative spelling ideaesthesia) is defined as a phenomenon in which activations of concepts (inducers) evoke perception-like experiences (concurrents). The name comes from the Greek idea and aisthesis, meaning "sensing concepts" or "sensing ideas", and was introduced by Danko Nikolić.
The experiment was reproduced in episode 3 of season 4 of the Netflix show Brain Games (National Geographic) with the names "takete" and "maluma." One participant expressed her association of takete and maluma with their respective shapes by comparing them to the rigid movement of a toy soldier and the swaying of the hula, respectively. A similar experiment included the association of the name "lomba" with a fictitious brand of milk chocolate and "kitiki" with a fictitious brand of dark chocolate.
- Köhler, Wolfgang (1929). Gestalt Psychology. New York: Liveright.
- Köhler, Wolfgang (1947). Gestalt Psychology (2nd ed.). New York: Liveright. p. 224.
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- Maurer, Daphne; Pathman, Thanujeni & Mondloch, Catherine J. (2006). "The shape of boubas: Sound-shape correspondences in toddlers and adults" (PDF). Developmental Science. 9 (3): 316–322. doi:10.1111/j.1467-7687.2006.00495.x. PMID 16669803. Archived (PDF) from the original on 2011-07-23.
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- D’Onofrio, Annette (2013). "Phonetic Detail and Dimensionality in Sound-shape Correspondences: Refining the Bouba-Kiki Paradigm". Language and Speech. 57 (3): 367–393. CiteSeerX 10.1.1.1020.1352. doi:10.1177/0023830913507694.
- McCormick, Kelly; Kim, Jee Young; List, Sara; Nygaard, Lynne C. (2015). "Sound to Meaning Mappings in the Bouba-Kiki Effect" (PDF). Proceedings of the 37th Annual Conference of the Cognitive Science Society: Mind, Technology, and Society: Pasadena, California, 23–25 July 2015. Austin, TX: Cognitive Science Society. pp. 1565–1570. ISBN 978-0-9911967-2-2.
- Bross, Fabian (2018). "Cognitive associations between vowel length and object size: A new feature contributing to a bouba/kiki effect". In Belz, M.; Mooshammer, C.; Fuchs, S.; Jannedy, S.; Rasskazova, O.; Zygis, M. (eds.). Proceedings of the Conference on Phonetics & Phonology in German-Speaking Countries. 13. Berlin: Humbold University. pp. 17–20.
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- Gómez Milán, E.; Iborra, O.; de Córdoba, M.J.; Juárez-Ramos, V.; Rodríguez Artacho, M.A.; Rubio, J.L. (2013). "The Kiki-Bouba effect: A case of personification and ideaesthesia". Journal of Consciousness Studies. 20 (1–2): 84–102.
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