Benders, T.
Center for Language Studies, Radboud University Nijmegen
It has been claimed that the intonation in infant-directed speech (IDS) expresses affect and that the enhanced auditory contrast between caregivers' corner vowels is to help their baby's language acquisition, but is unrelated to affect (Kuhl et al., 1997; Uther et al., 2007). However, our Study 1 shows that the vowels in Dutch IDS have reduced contrast, and that their acoustic properties are shaped by positive affect (on Norwegian, Englund & Behne, 2005/2006). Study 2 tests whether Dutch infants prefer speech with such happy-sounding vowels. Study 1 (completed). Eighteen Dutch mothers were recorded while speaking to their infant at 11 and 15 months and an adult. The results showed that: 1) The vowel space was smaller in IDS than in adult-directed speech (ADS); 2) The second formant (F2) of the vowels and center of gravity (CoG) of /s/ were higher in IDS; 3) F2 was higher to 11- than to 15-month olds. Because Dutch mothers reduce the auditory contrast between vowels in IDS, they do not seem to promote their infant's language development. A higher F2 and CoG are associated with the expression of positive emotions (Tartter & Braun, 1980; Kienast & Sendlmeier, 2000) and affect is expressed stronger to younger infants (Bornstein et al., 1992). Therefore, Dutch mothers' infant-directed vowels are primarily carriers of positive affect. Study 2 (in progress). Stimuli are normal sentences, sentences with enhanced intonation, and sentences with raised formants. In a preferential-listening procedure, Dutch 6-month-olds are expected to prefer the speech with enhanced intonation over the normal speech (Fernald & Kuhl, 1987; Singh et al., 2002). If infants also listen longer to speech with raised formants, they recognize positive affect from the vowels. Together, these studies test whether the affective character of IDS is, partly, contained in the realization of the vowels.