Do adults produce phonetic variants of /t/ less often in speech to children?

Abstract The surface phonetic details of an utterance affect how ‘native’ a speaker sounds. However, studies have shown that children’s acquisition of context-appropriate variation (sometimes called allophones) is late. This study’s goal was to understand how caregivers use phonetic variation in the production of American English /t/ in child-directed speech (CDS), compared to in adult-directed speech (ADS). We hypothesized that mothers modify their input to children in order to produce more limited variation in CDS than in ADS, to potentially assist children in the development of contrastive phonemic categories. To this end, we recorded eight mothers of children under the age of 2 years in both ADS and CDS conditions. Results reveal that CDS contains significantly more canonical cues to /t/ than ADS does, and fewer non-canonical cue patterns, including fewer unreleased tokens and fewer glottalized tokens in utterance-medial position. Also, we found larger aspiration duration differences in CDS between aspirated singleton [th] vs. unaspirated [t] in /st/ contexts, suggesting that mothers exaggerate this cue to the phonemic context in which the /t/ occurs. Overall, the findings suggest that CDS more clearly signals the phonemic category, which could in turn assist children learn the relationship between the underlying and surface forms.