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.
Four minute video:
https://youtu.be/CSp9ghRymgk
Wiki article:
https://en.wikipedia.org/wiki/Bouba/kiki_effect