Cross-linguistic differences in incremental planning under uncertainty

Language production often occurs under time pressure, leading speakers to initiate speech before fully formulating their message. Speakers can then continue planning their utterance incrementally, as more message information becomes available. We investigated how speakers use incremental planning to describe events under message uncertainty, and how planning strategies vary cross-linguistically. In Experiment 1, English speakers described animations of motion events (e.g., the butterfly moves to the slide), and we manipulated whether the target location was known from the trial onset or only disambiguated toward the end. When the target was initially uncertain, participants delayed speech onset but still began speaking before target disambiguation, starting with the available message information. Speakers also produced longer utterance durations and more pauses in uncertain trials, indicating incremental planning after speech began. In Experiment 2 we found that Spanish speakers planned more incrementally than English speakers, as Spanish word order allowed delaying production of the uncertain element - providing speakers with more time to incorporate it into their ongoing utterance after disambiguation. In Experiment 3 we asked whether Spanish speakers would pre-plan the gender-marked article of an uncertain target, if all potential targets matched in grammatical gender. There was no evidence that the gender-marked article was planned prior to target disambiguation, despite being shared across target options. Together, findings suggest that the balance between advance planning and incrementality depends on both message properties and language-specific grammatical affordances. These interactions highlight speakers' flexibility in adapting planning strategies to the production context, including in situations of message uncertainty.