Bouba, Kiki, and the Movement Between: Toward A Sensorimotor Hypothesis of Sound-Shape Cross-modal Correspondences

This study investigates the role of implicit motor dynamics in shaping cross-modal correspondences that underlie the Bouba/Kiki effect. Building on the hypothesis of a shared amodal code linking movement, sound, and shape, we conducted two behavioural experiments in which participants associated non-
words with either visual geometric shapes or friction sounds derived from hand-drawn movements. In both modalities, we observed systematic mappings consistent with the Bouba/Kiki pattern. Crucially, we manipulated the relative phase (RP) between the horizontal and vertical components of movement trajectories,
a key parameter describing spatial coordination. Results reveal that RP significantly predicts participants’ judgments across modalities, forming a continuous perceptual gradient from "Kiki" (angular, phase ≈ 0/π) to "Bouba" (rounded, phase ≈ π/2). These findings suggest that perceptual judgments are modulated not solely by sensory features, but by an internal motor representation of the movement that could have generated the stimulus. These preliminary findings support the existence of a motor-based, amodal code that structures cross-modal correspondences.