Synchrony is a construct that has been applied across the field of interpersonal relations. Condon and Sander (1974a, 1974b) first found a relationship between the movements of young infants and the prosodic patterns of adult speech. However, this result was controversial and attempts to replicate produced mixed results. Recent research on broader manifestations of synchrony in infant-parent interactions and work on human evolution of entrainment provide a background for the present study. This used motion-capture video technology and speech segmentation software to provide a more temporally precise analysis of interactional synchrony than could be obtained in earlier work. It also aimed to relate the narrow definition of synchrony with work using a broader conceptualisation. Mothers and infants were filmed interacting in a naturalistic setting. Movement velocity and acceleration, and phonetic boundaries and vocal intensity were used as the primary data, and time comparison of significant change points established. Initial results suggested an alignment of vocal and movement change points, but further analysis of the detailed time relationships between these two sets of data failed to show any significant patterns. It was concluded that interactional synchrony between infant movement and adult speech is simply an attractive illusion, and that any alignment between change points in the two spheres is simply due to the sheer number of such points, and extremely short time frames involved. These extremely short time frames are consistent with the significant results from previous studies, due to the cruder technology used. Methodological inconsistencies of previous studies are discussed, along with questions for future research.