THE ONTOGENY AND SIGNIFICANCE OF INFANTS FACIAL EXPRESSIONS IN THE FIRST 9 MONTHS OF LIFE

Four studies examined aspects of the differential emotions theory (DET ) hypothesis of expressive behavior development. In Study 1, facial-ex pressive movements of 108 2.5- to 9-month-old infants were video recor ded in positive and negative mother-infant interactions (conditions). As expected, Max-specified full-face and partial expressions of intere st, joy, sadness, and anger were morphologically stable between the 2 ages. Studies 1 and 2 confirmed predicted differential responding to m other sadness and anger expressions and to composite positive and nega tive conditions. Discrete negative expressions exceeded negative blend s, and the amount of both expression types remained stable across ages . Studies 3 and 4 provided varying degrees of support for the social v alidity of Max-specified infant negative affect expressions. Conclusio ns include revisions and clarifications of DET.