Why almost everyone agrees which curved shape is named 'Bouba'
Show people a jagged shape and a rounded shape, and ask which one is 'Bouba' and which is 'Kiki.' Over 95 percent of humans—across vastly different languages and cultures—assign 'Bouba' to the rounded shape and 'Kiki' to the spiky one. This Bouba/Kiki effect reveals that human brains map abstract visual shapes to specific speech sounds in a non-arbitrary, cross-sensory way.
The Island Experiment and the Birth of Sound Symbolism
In 1929, psychologist Wolfgang Köhler conducted an experiment on the island of Tenerife that challenged a central dogma of linguistics. He presented participants with two drawn figures—one composed of sharp, jagged spikes and the other of soft, undulating curves. Köhler asked subjects to assign two invented names, 'takete' and 'maluma,' to the figures. Without prior instruction, the vast majority of participants instinctively decided that the sharp figure was 'takete' and the rounded figure was 'maluma.'
At the time, mainstream linguistic theory held that the relationship between the sound of a word and its meaning was completely arbitrary. The fact that an English speaker calls a four-legged barking animal a 'dog' while a French speaker calls it a 'chien' was taken as proof that speech sounds bear no intrinsic connection to physical objects. Köhler's findings suggested something entirely different: human minds possess an intuitive, cross-sensory intuition that maps the abstract auditory properties of speech directly onto physical shapes.
From Maluma to Bouba and Kiki
Decades later, in 2001, neuroscientists Vilayanur S. Ramachandran and Edward Hubbard revisited Köhler's paradigm with a subtle variation. Using the nonsense words 'bouba' and 'kiki,' they tested both American college undergraduates and native Tamil speakers in India. Across both cultural groups, between 95 and 98 percent of participants identified the curvy, blob-like shape as 'bouba' and the sharp, starburst-like shape as 'kiki.'
By testing speakers of Tamil—a Dravidian language structurally and historically distinct from Indo-European languages—Ramachandran and Hubbard demonstrated that the effect was not merely a quirk of Western alphabets or English phonetics. The near-unanimous agreement across disparate language communities confirmed that the brain's association between speech sounds and geometric forms is a robust, universal psychological phenomenon.