Ternary meter from spatial sounds: Differences in neural entrainment between musicians and non-musicians.

The present study explores the relationship between the rhythmic structure of music and the spatial dimension of sound. We study how the brain interacts with spatially-separated sounds to build up a metrical structure. Participants listened to sequences of isochronous sounds that came from different positions on the azimuth plane: 0° (control condition), ±30°, ±60° or ±90° (spatial conditions). Ternary meter was signaled by the alternation of one sound on one side and two sounds on the symmetrical side. In Experiment 1, musicians and non-musicians paid attention to the spatial sounds. In Experiment 2, participants paid attention to a visual distractor. We recorded their electroencephalograms and performed frequency-tagging analyses. In both experiments, the isochronous beat elicited steady-state evoked-potentials at the frequency of the beat (2.4 Hz). While in Experiment 1 the alternation produced clear responses at the frequency of the ternary meter (0.8 Hz), in Experiment 2 these responses were only significant in the Spatial 90° condition, and mainly in musicians. This suggests that top-down attentional mechanisms are in play for meter induction. Besides, musicians showed stronger responses to beat and meter than non-musicians, suggesting that formal musical training enhances the neural entrainment to spatially-defined rhythms.