Speakers’ communicative intentions lead to acoustic adjustments in native and non-native directed speech

Speakers adapt acoustic features to factors such as listeners’ linguistic profiles. For instance, addressing a non-native listener elicits Non-Native Directed Speech (NNDS). However, whether these speech adaptations vary depending on the speakers’ didactic goals, in interaction with the listeners' profiles (i.e., native vs. non-native), remains unknown. We recorded native Spanish speakers naming novel objects to aid their listeners’ performance in comprehension, pronunciation, and writing tasks. Each speaker interacted with a native (Native Directed Speech, NDS) and a non-native (NNDS) Spanish listener. We extracted measures of vowel hyperarticulation, duration, intensity, speech rate, and F0 to assess listener- and task-specific speech adjustments. Our results showed that speakers hyperarticulated vowels to a greater extent in the writing condition compared to the comprehension condition, and during NNDS compared to NDS. Listener profile and task also impacted speakers’ F0 height, intensity, and vowel duration production. Therefore, speakers adjust acoustic features in their speech to achieve their didactic goals and accommodate their listener's profile. Also, speakers’ overall greater adaptation in NNDS than in NDS suggests that NNDS serves a didactic purpose.