Toddlers' sensitivity to phonetic detail in child speech.

Young language learners acquire their first language(s) from the speech they are exposed to in their environment. For at least some children (e.g., those in daycare), this environmental speech includes a large quantity of speech from other children. Yet, we know little about how young learners process this type of speech and its status as a source of input. Across two experiments, we assessed 21- to 23-month-olds' processing of a child's speech using the preferential looking paradigm. We found that toddlers processed the child speaker's productions as well as those of an adult and with the same level of sensitivity to phonetic detail previously shown for adult speakers. Although the amount of experience toddlers had interacting with other children outside the home had little influence on their processing of familiar words, only toddlers with high levels of experience with other children outside the home showed a disambiguation response after hearing novel labels. Whether this is truly due to the number or variety of other child speakers or to other correlated aspects of toddlers' language environments is unclear and remain intriguing questions for future research. Overall, these findings demonstrate that child speech may represent useful input for young language learners.