A new psychological experiment has shown that macaques may share with humans a way of associating certain sounds with specific geometric shapes, a phenomenon known since the 1920s in the "Buba and Kiki" experiment.
The origins of this idea go back to a famous experiment conducted about a century ago, in which people were asked to look at two shapes: one with pointed edges and the other with a smooth roundness, and then asked which one was called "Buba" and which one was called "Kiki".
It has been shown that the vast majority of people, regardless of their language or writing system, choose the name "Kiki" for the toothed shape, and "Buba" for the rounded shape.
In an attempt to explore whether this phenomenon is unique to humans or has deeper roots, a team of researchers conducted an experiment on nine monkeys living in the Mandai Wildlife Sanctuary in Singapore. The group included eight long-tailed macaques (Macaca fascicularis) and one southern pig macaque (Macaca nemestrina).
Before the actual test began, the researchers had to train the monkeys to participate in a neutral way that did not create any preconceived bias.
During the training phase, each monkey was placed in front of two cups covered with lids, with food under each lid. One lid was plain, while the other had a hybrid design combining pointed and rounded elements. No sound was played during this phase.
After the monkeys learned that the cup with the hybrid shape was the one containing the food, they moved on to the essential test.
In the next stage, the monkeys were presented with two cups, each with a lid in one of two typical shapes: either pointed or round, just like in the original "Buba and Kiki" experiment. During this test, an audio recording of the word "Buba" or "Kiki" played repeatedly in the background.
Each monkey underwent 24 trials, divided into short groups of three trials each, with the positions of the pointed and round shapes being changed, as well as the audio recording being switched between trials to ensure that the results were not biased.
The monkeys were not trained beforehand to consider any choice as "correct," but rather the goal was to monitor the choices they made automatically upon hearing each sound
The results showed a striking similarity to what is recorded in humans: in the vast majority of trials, the monkeys chose the round-shaped cover when they heard the word "Buba," and they chose the pointed-shaped cover when they heard the word "Kiki," and these choices were statistically higher than the percentage of random chance.
The researchers explained in their analysis that the probability of choosing the round shape was about 6 times higher in Buba's attempts compared to Kiki's attempts.
The research team believes that these results support the idea that some forms of correspondence between different senses (such as sound and shape) may not be acquired solely through human language or culture, but may be due to innate perceptual biases inherited from a distant common ancestor between humans and other primates.
The researchers add that this discovery shifts the evolutionary question from "Is this phenomenon unique to humans?" to "How widespread are these cognitive similarities among vertebrates as a whole?"
It is worth noting that this study has not yet undergone scientific review, but a preliminary version can be viewed via the journal bioRxiv, and future trials with larger numbers of subjects are needed to confirm the results more clearly.
