Conversation, gaze coordination, and beliefs about visual context.

Conversation is supported by the beliefs that people have in common and the perceptual experience that they share. The visual context of a conversation has two aspects: the information that is available to each conversant, and their beliefs about what is present for each other. In our experiment, we separated these factors for the first time and examined their impact on a spontaneous conversation. We manipulated the fact that a visual scene was shared or not and the belief that a visual scene was shared or not. Participants watched videos of actors talking about a controversial topic, then discussed their own views while looking at either a blank screen or the actors. Each believed (correctly or not) that their partner was either looking at a blank screen or the same images. We recorded conversants' eye movements, quantified how they were coordinated, and analyzed their speech patterns. Gaze coordination has been shown to be causally related to the knowledge people share before a conversation, and the information they later recall. Here, we found that both the presence of the visual scene, and beliefs about its presence for another, influenced language use and gaze coordination.