Geometric properties of musical scales constitute a representational primitive in melodic processing.

Uncovering the mental representations underlying symbolic domains is a long-standing goal of cognitive science. Music, a relatively unexplored aspect of cognition, presents a unique testbed for understanding the format of symbolic representations. Theoretical accounts have emphasized the geometric structure underlying musical scales, yet empirical work directly engaging with these structures remains limited. Based on data collected from 961 participants across four experiments, we demonstrate that certain geometric structures strongly modulate perceptual sensitivity to out-of-scale notes in melodies. Furthermore, we show that geometric regularity predicts sensitivity to note deviations across diverse musical structures. Crucially, these effects persist even in an entirely unfamiliar tuning system, suggesting the role of specific geometric properties independent of learned cultural associations. Our findings situate scale geometry as a critical, time-invariant representation in melodic processing and reveal organizational principles that may underlie mental representations across domains.