With National Science Foundation support, Dr. Jeffrey T. Runner will conduct three years of linguistic research examining how participants interpret sentences containing a range of different elided phrases. Many of the proposed experiments will use a lightweight head-mounted eye tracker to monitor eye movements as participants identify an object or a person in a scene while listening to descriptions of the depicted activities (e.g., "The security guard opened the lock and the night watchman did, too."). Which object or person participants look at, and when they look at them, provides evidence about which referents they are considering as they interpret the elided expressions. The goals of this research are to (a) investigate the interpretation of these expressions with on-line and off-line tasks; (b) evaluate the extent to which grammatical factors define the potential set of referents for elided phrases and pronouns; and (c) examine the interaction of these grammatical factors with pragmatic and discourse factors. The results of this research will be important for understanding how people assign reference, which is a central goal of current research in theoretical and applied linguistics. Very little research has been devoted to using a range of different expressions to explicitly address these questions. A better understanding of reference resolution can also benefit research in other domains. Reference resolution is one of the most central and challenging problems in developing efficient language understanding systems, including systems that are being developed for health-related bio-medical applications. Moreover, information about the timing of eye movements and speech, especially in relation to reference resolution, will also inform scientists who are developing computer-based language understanding systems that use eye movements to help resolve ambiguous words and referring expressions. Furthermore, difficulties in reference resolution are associated with, and often used to diagnose, certain language difficulties that arise due to brain damage, and thus a better understanding of the grammatical and discourse factors guiding reference resolution can prove a useful baseline for clinical research.