Dementia will develop in 5% to 11% of people over the age of 65 and will affect as many as 50% of those over age 85. Alzheimer's disease (AD) is the most common cause of dementia. Investigating false recognition in AD is important in understanding clinical false memories and in interpreting the results of memory tests used in research and clinical care. Previously we focused on false memories which occur when subjects falsely recognize items because they share the general meaning, idea, or gist conveyed by a collection of items (gist information). The proposed experiments will use the techniques of experimental psychology and cognitive neuroscience (including event-related potentials, ERPs) to investigate the more fundamental issue of the false recognition of unrelated items (the baseline rate of false alarms) in AD. As false alarms are a reflection of the response bias (or tendency to respond "old"), this proposal will critically examine this bias in AD. Aim 1 will investigate whether AD patients are able to shift to a more conservative response bias. Expt. 1 will examine response bias at varying levels of discrimination, and will correlate this bias with frontal lobe function and awareness of the patients'memory deficit. Expt. 2 will use ERPs to examine response bias when AD patients are told that a lower proportion of studied items are present than actually are. Aim 2 will investigate whether AD patients are impaired in their ability to inhibit responding "old" on the basis of weak cues. Expts. 3 &4 will use behavioral and ERP responses to examine whether AD patients are more likely than older adults to respond "old" when items are made more familiar by increasing the presentation time or perceptual clarity of the test item. Expt. 5 examines whether AD patients can correctly attribute the source of their familiarity. Aim 3 will investigate whether the disordered semantic networks present in AD lead to an aberrant sense of familiarity and to increased false recognition. Expts. 6 &7 will examine AD patients'reaction time, N400 ERP responses, and false recognition of weak semantic associates. Aim 4 will investigate the use of a distinctiveness heuristic in AD whereby subjects may lower their false recognition using the rule of thumb, "If I had seen it before I would have remembered it." Expts. 8 &9 will use behavioral and ERP responses to examine whether AD patients can use this heuristic to reduce their false recognition and whether its use correlates with the patients'awareness of their memory deficit. Taken together, the proposed studies will provide new insights into memory in AD which may lead to improvements in our research and clinical care of patients with AD.