The scope of audience design in child-directed speech: Parents’ tailoring of word lengths for adult versus child listeners.

When communicating with other people, adults reduce or lengthen words based on their predictability, frequency, and discourse status. But younger listeners have less experience than older listeners in processing speech variation across time. In 2 experiments, we tested whether English-speaking parents reduce word durations differently across utterances in child-directed speech (CDS) versus adult-directed speech (ADS). In a child-friendly game with an array of objects and destinations, adult participants (N = 48) read instructions to an experimenter (adult-directed) and then to their own 2- to 3-year-old children (child-directed). In Experiment 1, speakers produced sentences containing high-frequency target nouns, and in Experiment 2, they produced sentences containing low-frequency target nouns. In both CDS and ADS in both experiments, speakers reduced repeated mentions of target nouns across successive utterances. However, speakers reduced less in CDS than in ADS, and low-frequency nouns in CDS were overall longer than low-frequency nouns in ADS. Together, the results suggest that repetition reduction may be beyond speaker control, but that speakers still engage in audience design when producing words for relatively inexperienced listeners. We conclude that language production involves nested audience-driven and speaker-driven processes.