Co-speech gesture projection: Evidence from inferential judgments

The nature of the semantic contribution of co-speech gestures has been the subject of recent theoretical and experimental investigation. Such gestures have been reported to give rise to cosuppositional inferences that can project out of certain linguistic environments, much in the way that presuppositions of verbal expressions do (Schlenker 2018a; b). For example, a sentence like John will not [use the stairs]_UP, produced with a finger pointed upwards while pronouncing the verb phrase, is argued to give rise to the inference that if John were to use the stairs, he would go up the stairs. lieu et al. (2017) investigated the projection properties of directional inferences associated with the gestures UP and DOWN, using a Truth Value Judgment Task and a Picture Selection Task, and reported the presence of existential projection of the gestural inferences out of quantified environments. We investigated the same gestural inferences using a method that more closely tracks the introspective judgments reported in the literature on gesture projection. Participants were presented with an Inferential Judgment Task, in which they had to rate the strength of inferences arising from UP and DOWN in six different linguistic environments. Using this task, we observed projection of the conditional inference from the scope of negation and universal projection of the inference from the scope of none and exactly one, as well as suggestive evidence that the inference can be locally accommodated in the scope of negation and none. These main findings would be difficult to explain if gestures were posited to make at-issue contributions; the finding of local accommodation is also not straightforwardly explained on the view that co-speech gestures contribute supplement-like meanings (Ebert & Ebert 2014). On the other hand, both main findings are compatible with the view that co-speech gestures trigger cosuppositions.