Macaques match sounds to shapes like humans do, study finds

SINGAPORE — Macaques at Singapore's Mandai Wildlife Reserve have been shown to associate certain sounds with specific geometric shapes in a manner similar to humans, according to a new study. In the experiment, researchers trained nine long-tailed and pig-tailed macaques using a hybrid shape that combined sharp and rounded elements; the food container with the hybrid shape was used in the training phase, with no sounds played during that stage. In the main test, each macaque was presented with two containers, one sharp and one rounded, while either "buba" or "kiki" sounds were played. Over 24 trials per animal, the macaques largely picked the rounded container when they heard "buba" and the sharp container when they heard "kiki." The researchers reported that the rounded shape was chosen at roughly six times the rate in the "buba" trials compared with the "kiki" trials. The study tested the so-called "buba-kiki" effect, a sound-shape association documented in humans since the 1920s. The findings have not yet been peer-reviewed; the paper is available as a preprint on bioRxiv.