Lyn Tieu, Robert Pasternak, Philippe Schlenker, & Emmanuel Chemla. 2017. “Co-speech gesture projection: Evidence from inferential judgments.”

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Abstract: Co-speech gestures have been reported to give rise to so-called cosuppositional inferences (Schlenker 2015, 2016). For example, a sentence like “John will not [use the stairs] UP”, produced with an UP gesture (finger pointed upwards) co-occurring with the verb phrase is argued to give rise to the conditional presupposition that if John were to use the stairs, he would go up the stairs. Such a presuppositional treatment of the gestural inference predicts that it should project out of certain linguistic environments. We tested this prediction using an Inferential Judgment Task, in which participants had to rate the strength of inferences arising from the use of the co-speech gestures UP and DOWN, when produced with the predicate “use the stairs”, in six different linguistic environments: plain affirmative and negative sentences, modal sentences containing “might”, and quantified sentences involving “each”, “none”, and “exactly one”. The results provide evidence that the conditional inference projects from the scope of negation, and projects universally from the scope of “none” and “exactly one”. In addition, the data suggest that the cosupposition can also be locally accommodated in the scope of negation and “none”. Both findings are compatible with the view that co-speech gestures trigger cosuppositions, and are incompatible with the view that gestures merely make at-issue contributions. We discuss their relevance for a third theory of co-speech gestures, according to which their meanings are supplements, just like those of appositive relative clauses (Ebert & Ebert 2014). While some choice points in the Supplemental theory can arguably lead to appropriate predictions regarding patterns of projection, it is not clear that the theory can account for the existence of local accommodation in the sentences under consideration. Finally, we compare our findings to those of Tieu et al. (2017), who tested the very same sentences using a truth value judgment task and a picture selection task, and found evidence for existential rather than universal projection (along with local accommodation).

Keywords: gesture; co-speech gestures; presupposition; projection; local accommodation