Pitch-size and Bouba-Kiki studies of crossmodal correspondences in neonatal domestic chicks reveal adaptive prioritization of multisensory integration

The question of which perceptual associations are available to a neonatal organism, and which are not, sits at the heart of debates about the evolutionary origins of multisensory integration. Crossmodal correspondences, the systematic tendency to treat stimuli from different sensory modalities as perceptually compatible, have been documented across a growing number of species, suggesting they reflect an evolutionarily conserved feature of vertebrate perception rather than a product of linguistic or cultural experience. Yet the comparative literature reveals a pattern that has not been adequately theorized: even within a single species, tested at the same developmental stage with equivalent methodology, some crossmodal correspondences emerge spontaneously while others do not. The present study investigated this question by testing the same cohort of three-day-old domestic chicks (Gallus gallus domesticus) on two distinct crossmodal correspondence tasks in a within-subject design: a pitch-size correspondence, paralleling the magnitude mapping first identified by Sapir, and a sound-size correspondence modeled on the magnitude logic of the Bouba-Kiki effect. By directly comparing performance on both tasks within the same individuals, and situating the findings alongside the broader comparative literature on crossmodal correspondence in non-human animals, this study examines whether crossmodal sensitivity in the neonatal chick reflects a unified, domain-general perceptual faculty or a set of independently emerging, ecologically tuned abilities. This study proposes an adaptive prioritization framework, under which the developmental expression of crossmodal correspondences is governed not by their ecological validity alone, but by the immediacy and urgency of the behavioral demands each correspondence serves at the specific developmental moment of hatching. These findings contribute to a growing body of evidence suggesting that the neonatal perceptual system is neither a blank slate nor a fully formed architecture, but a selectively organized one, shaped from the earliest moments of life by the adaptive demands of hatching.