Abstract Adults and children across different cultures speak to infants and young children with a special child-directed register characterized by higher and more varied pitch. The function of the acoustic modifications in child-directed speech has been a long-standing issue. The Hyperarticulation theory proposes that child-directed speech enhances the important cues for speech and language processing, which promotes language acquisition. The Affect theory postulates that affectionate emotions conveyed in child-directed speech capture children’s attention and promote language learning. This talk will present two studies. The first study tested these two competing theories by comparing the perceptual and acoustic-phonetic characteristics of child-directed and [...]