Spatial associations for slow musical tempos are revealed by increased stimulus density.

Recent evidence suggests the existence of spatial associations for musical tempo, characterized by faster left-key responses to relatively slow tempos and faster right-key responses to relatively fast tempos. However, while this effect has been consistently observed in the fast tempo range (133-201 bpm), previous studies investigating the slow tempo range (e.g., 40-104 bpm) have failed to find a reliable effect, reporting null or contradictory findings. The present study investigated whether a spatial association exists in the slow tempo range when specific methodological limitations (i.e. excessive gaps between stimuli) are addressed. Specifically, the study aimed to increase stimulus density through two complementary approaches: (1) testing the "absolute gap hypothesis" by using a physically linear scale with reduced intervals ("physical linearity condition"), and (2) testing the "proportional gap hypothesis" by using a perceptually linear scale based on Weber's Law ("perceptual linearity condition"). The results revealed a significant spatial association in both conditions, demonstrating that a denser set of stimuli facilitates the emergence of spatial mappings regardless of the scaling method. These findings demonstrate that ensuring temporal continuity through increased stimulus density reveals a robust spatial association in the slow tempo range, thereby supporting a unified mechanism for temporal processing consistent with a generalized magnitude system.