“…The driving forces behind the acoustic characteristics of this special register, variably referred to as motherese, baby talk, or infant-directed speech ͑IDS͒, have long been the object of speculation. Most researchers agree that caregivers adapt their speech in order to engage their children's attention and maintain positive rapport by enhancing the expression of emotion and affect ͑Fer-nald, 1989͑Fer-nald, , 1992Fernald and Simon, 1984;Kaplan et al, 1991;Stern et al, 1982;Uther et al, 2007͒. In addition, some researchers further hypothesize that IDS may also serve to facilitate language acquisition ͑Englund, 2005; Englund and Behne, 2006;Fernald, 2000;Liu et al, 2007;Sundberg, 2001;Werker et al, 2007͒. While the idea that caregivers may enhance linguistic categories when addressing their children is as old as the concept of IDS itself ͑see e.g., Ferguson, 1964͒, it was only recently that researchers turned to the acoustic signal as a possible level at which this enhancement may apply. This recent work indeed suggests that across-category acoustic distance is augmented in speech to infants when vowels and tones are measured ͑on vowels: Burnham et al, 2002;Kirchhoff and Schimmel, 2005;Kuhl et al, 1997; but see Englund and Behne, 2006;on tones: Liu et al, 2007on tones: Liu et al, , 2009; but see Kitamura et al, 2001;Papoušek and Hwang, 1991͒. In contrast, consonantal contrasts have received less attention, and the little work on them has reported conflicting results: some report enhancement ͑e.g., Malsheen, 1980;Sundberg, 2001͒, and others no difference or even deterioration ͑e.g., Baran et al, 1977;Sundberg and Lacerda, 1999͒. Given that consonants play a fundamental role in wordlearning and lexical access, both in childhood and later on ͑to give just a few examples, Cutler et al, 2000;Nazzi, 2005;New et al, 2008͒, it is important to assess the possibility that consonantal categories may be enhanced in speech addressed to young children.…”