Authors:Gregory A. Bryant, Pierre Liénard and H. Clark Barrett
When communicating with infants, caregivers often modulate their speech in an effort to make their communicative and informative intentions more clear. Infant-directed (ID) speech differs acoustically from adult-directed (AD) speech, and systematically varies according to different kinds of intentions. This way of speaking to infants is thought to be a species-specific adaptation, as research has documented highly similar patterns in ID speech across a variety of cultures. A recent study has also shown that people from an indigenous non-Western culture (Shuar of Amazonian Ecuador) can reliably discriminate ID speech from AD speech in a language they do not speak, and distinguish between four different intention categories (prohibition, attention, comfort, and approval). The current research attempted to replicate this finding in a traditional African population, the Turkana of northwestern Kenya. In three experiments, we found that Turkana adults were able to discriminate between ID and AD speech produced in English by American mothers, and they could also distinguish between several intention categories in both ID and AD speech. Signal detection analysis revealed that ID speech was marginally more discriminable than AD speech, but overall rate of intention recognition was similar across speech types. These results partially support the hypothesis that ID speech is universally recognizable due to the formfunction relationship between acoustic signals and their communicative purpose, but there were differences in performance between Turkana and Shuar that merit further investigation.