Micro-variations in timing and loudness affect music-evoked mental imagery.

Music can shape the vividness, sentiment, and content of directed mental imagery. Yet, the role of specific musical features in these effects remains elusive. One important aspect of human musical performances is the presence of micro-variations-small deviations in timbre, pitch, and timing, driven by motor and attentional processes. These variations enhance perceived "naturalness" compared to mechanical playing without such variations. Here, we investigated whether random micro-variation, as opposed to mechanical playing, affects mental imagery characteristics. One hundred participants performed a directed mental imagery task where they imagined a journey, accompanied either by drumming with micro-variation, drumming without micro-variation, or silence. Participants rated the vividness, distance and time travelled of their imagined content, alongside free-format content responses. Bayesian multilevel regression model showed that repetitive quasi-isochronous drumming enhanced mental imagery vividness, with a stronger effect observed when the drumming contained random micro-variation. Drumming with random micro-variation also increased imagined distance and time travelled compared with silence. Furthermore, individual traits in absorption, ability to imagine vividly, and level of musical training interacted with auditory conditions to further shape mental imagery characteristics. The findings have implications for the use of music to support imagery in creative, recreational, and therapeutic settings.