Infant language learning depends on the distribution of co-occurrences within language-between words and other words-and between language content and events in the world. Yet infant-directed speech is not limited to words that refer to perceivable objects and actions. Rather, caregivers' utterances contain a range of syntactic forms and expressions with diverse attentional, regulatory, social, and referential functions. We conducted a distributional analysis of linguistic content types at the utterance level, and demonstrated that a wide range of content types in maternal speech can be distinguished by their distribution in sequences of utterances and by their patterns of co-occurrence with infants' actions. We observed free-play sessions of 38 12-month-old infants and their mothers, annotated maternal utterances for 10 content types, and coded infants' gaze target and object handling. Results show that all content types tended to repeat in consecutive utterances, whereas preferred transitions between different content types reflected sequences from attention-capturing to directing and then descriptive utterances. Specific content types were associated with infants' engagement with objects (declaratives, descriptions, object names), with disengagement from objects (talk about attention, infant's name), and with infants' gaze at the mother (affirmations). We discuss how structured discourse might facilitate language acquisition by making speech input more predictable and/or by providing clues about high-level form-function mappings.

Children show a remarkable degree of consistency in learning some words earlier than others. What patterns of word usage predict variations among words in age of acquisition? We use distributional analysis of a naturalistic corpus of child-directed speech to create quantitative features representing natural variability in word contexts. We evaluate two sets of features: One set is generated from the distribution of words into frames defined by the two adjacent words. These features primarily encode syntactic aspects of word usage. The other set is generated from non-adjacent co-occurrences between words. These features encode complementary thematic aspects of word usage. Regression models using these distributional features to predict age of acquisition of 656 early-acquired English words indicate that both types of features improve predictions over simpler models based on frequency and appearance in salient or simple utterance contexts. Syntactic features were stronger predictors of children's production than comprehension, whereas thematic features were stronger predictors of comprehension. Overall, earlier acquisition was predicted by features representing frames that select for nouns and verbs, and by thematic content related to food and face-to-face play topics; later acquisition was predicted by features representing frames that select for pronouns and question words, and by content related to narratives and object play.

The process by which infants learn verbs through daily social interactions is not well-understood. This study investigated caregivers' use of verbs, which have highly abstract meanings, during unscripted toy-play. We examined how verbs co-occurred with distributional and embodied factors including pronouns, caregivers' manual actions, and infants' locomotion, gaze, and object-touching. Object-action verbs were used significantly more often during caregiver-infant joint attention interactions. Movement and cognition verbs showed distinct co-occurrences with different contexts. Cognition and volition verbs were differentiated by pronouns. These findings provide evidence for how verb acquisition may be supported by the distributional and embodied contexts in caregiver-infant interactions.