Body percussion and the biomechanical calibration of musical meter: the somatic externalization of meter hypothesis

Musical meter takes specific forms, a preferred tempo and a small set of stable subdivisions, that existing accounts do not fully explain. I propose the Somatic Externalization of Meter (SEM) hypothesis: that these parameters are calibrated to the oscillatory dynamics of the moving body, so meter inherits the characteristic periods of the limbs. The proposal comprises a well-supported causal claim that bodily and vestibular state shape how an ambiguous rhythm is heard, a central mechanistic claim that beat perception is parameterized by effector biomechanics, and a conjectural claim about manufactured percussion. Body percussion is the diagnostic case, in which effector and instrument coincide, giving a zero-offset baseline against which instrumental displacement is measured. I recast the mechanistic claim as a measurable quantity, biomechanical transparency, which admits a strict null, and set out eight falsifiable predictions. Two existing findings run against the hypothesis and are reported.