They mention this in the article: This process could also account for the classic “cross-modal” finding, first reported in 1929 and replicated around the world

They mention this in the article: This process could also account for the classic “cross-modal” finding, first reported in 1929 and replicated around the world many times since, that people tend to pair a blobby shape with a word-sound like “bouba” and a spiky shape with a word like “kiki”.