Chickens show bouba/kiki effect, challenging human uniqueness

Newly hatched chickens show the bouba/kiki effect

Researchers have discovered that even newly hatched chickens associate the nonsense word “bouba” with round shapes and “kiki” with spiky ones. This finding, published in Science, challenges the long-held idea that this sound-shape association is a uniquely human trait linked to complex language.

The phenomenon, known as the bouba/kiki effect, was first documented in 1947. Studies have consistently shown that people across languages and cultures, including infants as young as four months old, make this association. However, previous attempts to find it in other primates failed.

Testing instincts in baby chicks

A research team in Italy tested one- and three-day-old chicks to see if the effect exists beyond primates. Chickens are an ideal model because, unlike human infants, they are mobile and can interact with their environment immediately after hatching.

The team placed chicks in an arena with two shapes—one round and one spiky—and played audio recordings. When a recording of a person saying “bouba” was played, 80 percent of the chicks moved toward the rounded shape first. When “kiki” was played, that number dropped to 25 percent.

The effect was slightly stronger in three-day-old chicks but was clearly present in chicks tested just one day after hatching. Control tests with silence or classical music showed the chicks had only a mild innate preference for the rounded shape.

What the bouba/kiki effect really is

The researchers argue the effect is a “crossmodal correspondence,” where input from one sense influences perception in another. This is a basic brain function not exclusive to language.

Other examples of crossmodal correspondences found in animals include:

• Associating high-pitched sounds with small objects and low-pitched sounds with large ones.
• Linking high pitches with bright lighting, observed in species from chimpanzees to tortoises.

The chicken study suggests the bouba/kiki effect is a similar, fundamental sensory link. Its absence in prior primate studies may be because tested adults had complex motivations that overrode simple instinctual preferences.

Why this finding matters

This evidence strongly indicates the bouba/kiki effect is not a special capacity underpinning sophisticated human language. Instead, it appears to be a widespread sensory processing mechanism that can emerge in animals without language.

The study implies that the neural architecture for linking abstract sounds with shapes is ancient and shared across species. It reshapes our understanding of a classic psychological effect, moving it from the realm of language to the realm of basic perception.

The research was published in Science with the DOI 10.1126/science.adq7188.