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In the humanities in general and psychology in particular, it is rare for a research study to be considered decisive in the sense that it forces researchers to change generally accepted theoretical positions. Such is the case, though, for example, with Köhler’s problem situations, which indicate the existence of representations in chimpanzees, or of Piaget’s search for hidden object situations. The study by DeCasper and Fifer (1980), along with those that followed it, can also be numbered among these few decisive works. Their experiments show the existence of prenatal learning of characteristics of the mother’s voice which allows the baby after birth, and thus in different acoustic conditions, to differentiate this voice from an unfamiliar one. This article attempts to situate the main theoretical consequences of this discovery, which have been taken into account very insufficiently in the literature.