Staying offbeat: sensorimotor syncopation with structured and unstructured auditory sequences

Three experiments investigated whether adding metric (higher-order, periodic) structure to tone sequences stabilizes syncopated finger tapping. Participants tapped in antiphase with metronomic tone sequences in which accents--produced by sounding two tones simultaneously--occurred regularly every two, three, or four tones (metric), occurred unpredictably (irregular), occurred on every tone (heavy beat), or were absent (light beat). Tap timing variability, although commensurate with metric and light beat sequences, was lower with metric than with heavy beat and irregular sequences even when the instructions specified using metric grouping in all conditions. Higher-order periodic fluctuations (delays) in tap timing--found only in metric conditions--were associated with low overall tap timing variability, suggesting that a regularly applied, meter-based phase-resetting mechanism stabilizes syncopation.