Visible pre-acoustic lip motion aids listeners’ judgments of speech onset times.

Interlocutors in conversation coordinate to achieve very short transitions between acoustic turns. The mechanisms supporting this coordination remain an area of active investigation. A large body of work has considered the cues that might clue next speakers (i.e., interlocutors awaiting their upcoming turn in conversation) that the floor is about to be yielded. Less attention has been given to the cues that next speakers might emit when preparing to take the floor. Most work that has considered cues from next speakers has emphasized manual gestures and nonspeech facial movements, and it has seldom examined the effects of these cues on onlookers. The present study proceeded from the insight that kinematic speech articulation necessarily precedes the onset of phonation, at the beginning of a new turn. Across four web-based experiments (total N = 171), participants viewed the beginnings of speech turns drawn from an audiovisual database of natural two-way conversations. In all experiments, participants were tasked with timing keypresses to coincide with audible speech onset. Visibility of facial movements (including lip movements) was manipulated. Experiment 1 compared clips with digitally obscured and unobscured faces. Experiments 2-4 compared clips that did or did not include isolated visualizations of lip movements. Experiment 3 varied the presence of speech audio, and Experiment 4 manipulated whether initial lip position was informative to the target utterance. Overall, findings suggest that visible lip motion facilitates detecting acoustic speech onset, especially if that motion is directly relevant to the speaker's phonetic goals. Implications for conversational turn-taking are discussed. (PsycInfo Database Record (c) 2025 APA, all rights reserved).