Infant Rhythmic Movement Across Postural Conditions

Musical engagement is a universal trait of human behavior and a foundational form of embodied communication. While this engagement is deeply rooted in bodily experiences, much of the existing research has focused on perceptual and neural mechanisms, with comparatively little attention paid to how the body's physical affordances, including the differing biomechanical properties of distinct effectors, shape early rhythmic engagement with music. The current study aims to characterize how rhythmic motoric responses to music vary in the context of an infant's developing physical skills and attributes. Pre-ambulatory infants were placed in an unweighting paradigm to vary levels of postural support as duration and rate of rhythmic movement were measured across core and distal effectors. Results indicated that greater postural support resulted in increased durations and quicker rates of rhythmic movement and enabled qualities of bounce and rebound within infants' movement repertoire, an effect driven primarily by core effectors. Rate of rhythmic movement was found to be organized primarily by effector type, with core movements consistently slower than distal movements across all conditions. Distinct trends between core and distal effectors were found, with vertically displaced core movements consistently slower in rate and increased in duration with age, while distal movements were faster in rate and showed no significant change in duration with age. These patterns align with principles of biomechanics and mass distribution, reflecting a hierarchical organization of rhythmic movement across the body that parallels patterns observed in adults. Findings suggest that postural support facilitates the emergence of more fully embodied musical engagement, offering insight into the sensorimotor foundations of early rhythmic movement.