Tracking Colisteners' Knowledge States During Language Comprehension.

When we receive information in the presence of other people, are we sensitive to what they do or do not understand? In two event-related-potential experiments, participants read implausible sentences (e.g., "The girl had a little beak") in contexts that rendered them plausible (e.g., "The girl dressed up as a canary for Halloween"). No semantic-processing difficulty (no N400 effect) ensued when they read the sentences while alone in the room. However, when a confederate was present who did not receive the contexts so that the critical sentences were implausible for him or her, participants exhibited processing difficulty: the social-N400 effect. This effect was obtained when participants were instructed to adopt the confederate's perspective-and critically, even without such instructions-but not when performing a demanding comprehension task. Thus, unless mental resources are limited, comprehenders engage in modeling the minds not only of those individuals with whom they directly interact but also of those individuals who are merely present during the linguistic exchange.