Bidirectional effects of speech and gesture: evidence from a novel levels-of-congruence paradigm.

Introduction: Previous research has shown that speech and gesture are integrated during comprehension, with differences in response times and electrophysiological activity observed between incongruent and congruent gesture-speech pairings. Beyond these incongruency effects, it remains unclear whether comprehenders use gestures to adapt or extend conventional interpretations for novel communicative purposes. Method: The current study examined the bidirectional influence of speech and gesture by employing a novel levels-of-congruence paradigm, in which the same metaphor (e.g., Results: In Experiments 1 and 2, participants consistently rated the preferred interpretation as the most meaningful and selected it most often across all gesture conditions. However, gestures depicting the possible interpretation significantly increased both the meaningfulness ratings and the likelihood of being selected of the possible interpretation. In Experiment 3, the presence of speech cues significantly increased ratings for the alternative interpretation compared with the condition without additional cues. Discussion: These findings demonstrate bidirectional interactions between speech and gesture during metaphor comprehension. Gestures constrained metaphor interpretation, whereas speech broadened the range of interpretations attributed to gestures. Overall, the results support the integrated-systems hypothesis by showing that speech and gesture jointly contribute to the construction of meaning.