Hearing shapes: the Bouba–Kiki effect in adult domestic dogs

The ‘Bouba–Kiki effect’ is an example of spontaneous association between auditory and visual stimuli, described in humans as a case of sound symbolism, a predisposition linked to language. Recent evidence showed that 3-day-old chicks also exhibit a spontaneous association between round and spiky shapes and the sounds ‘Bouba’ and ‘Kiki,’ respectively, thus suggesting that the effect may rather be an instance of a more widespread cross-modal correspondence. We investigated whether the Bouba–Kiki effect is present in adult domestic dogs (Canis familiaris) by investigating dogs’ spontaneous tendency to associate a spiky or a rounded shape to the ‘Bouba’ and ‘Kiki’ sounds. Dogs looked significantly more at the rounded shape while ‘Bouba’ was played, and they looked at and explored the spiky shape when ‘Kiki’ was played. Our results suggest that a spontaneous sound–shape association akin to that of humans is also present in adult domestic dogs. Further studies are needed to investigate the function and ontogenesis of this cognitive process.