This paper provides an overview of an interdisciplinary programme of research started more than 20 years ago at the University of Tokyo. A major aim of this programme was (and still is) to develop methods and related forms of quantitative analysis that provide rigorous evaluations of infant behaviour from a particular theoretical perspective. In one part of the programme telethermography is used to measure emotional changes in young infants. Contrary to the accepted view in attachment theory, infants as young as 2–3 months showed evidence of stress following separation from the mother (as indexed by a drop in the skin temperature of the infant's forehead). In another part, we established the presence of interpersonal synchrony between arm movements of the newborn and the speech of the mother and other adults, using computer assisted pattern recognition techniques. On the basis of this finding, we have proposed a simulation model of mother-infant interaction from the perspective of system information theory. In general, our programme of research provides a theoretically driven set of techniques and analytical approaches that may provide deeper insights into early development and parenting.