The goal of the research is to discover the mental mechanisms that allow people to communicate with language. The proposed experiments will use an eyetracking devise to investigate the way people take the other's perspective during conversation. The experiments will test a new theory: The Adaptive Language Use theory. The theory assumes that perspective information is used in conversation as function of the diagnosticity of perspective, and that language users adapt to structures in the environment that affect this diagnosticity. So if the diagnosticity of perspective changes over time, the theory predicts that conversants will adapt their use of perspective accordingly. The experiments will use a relatively novel methodology to investigate mental processes on-line during a real conversation. This would allow the application of the results to real life conversations in a variety of social settings. The proposed studies promise to have important societal and health implications. Understanding the mental mechanisms of linguistic communication and the conditions for their success and failure could be relevant to models of coordination of action such as "game theory," which is studied in a variety of the social sciences, from economics to international relations. In order to coordinate action, then, people can signal their intentions in a variety of ways, thereby making communication critical to people's ability to coordinate and cooperate. This research will allow a better understanding of the mental mechanisms that underlie such interaction and the way environmental conditions mold interpersonal perspective taking. With such knowledge, we will be better equipped to create appropriate circumstances that could facilitate successful communication and minimize systematic misunderstanding. This knowledge could be applied to promote more successful interactions in health related settings such as doctor-patient communication.