We examined whether evidence for prosodic signals about shared belief can be quantitatively found within the acoustic signal of infant-directed speech. Two transcripts of infant-directed speech for infants aged 1;4 and 1;6 were labeled with distinct speaker intents to modify shared beliefs, based on Pierrehumbert and Hirschberg's theory of the meaning of prosody [1]. Acoustic predictions were made from intent labels first within a simple single-tone model that reflected only whether the speaker intended to add a word's information to the discourse (high tone, H{sup}*) or not (low tone, L{sup}*). We also predicted pitch within a more complicated five-category model that added intents to suggest a word as one of several possible alternatives (L{sup}*+H), a contrasting alternative (L+H{sup}*), or something about which the listener should make an inference (H{sup}*+L). The acoustic signal was then manually segmented and automatically classified based solely on whether the pitches at the beginning, end, and peak intensity points of stressed syllables in salient words, were closer to the utterance's pitch minimum or maximum on a log scale. Evidence supporting our intent-based pitch predictions was found for L{sup}*, H{sup}*, and L{sup}*+H accents, but not for L+H{sup}* or H{sup}*+L. No evidence was found to support the hypothesis that infant-directed speech simplifies two-tone into single-tone pitch accents.
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