Individuals with PTSD report intense negative emotional reactions when reminded of their trauma and a lack of ability to experience and express emotions, or "emotional numbing." Although there has been extensive research conducted on conditioned negative emotional response to reminders of trauma, there has been little research on emotional numbing, and sparse research on the relationship between these two response classes. The goal of this proposal is to demonstrate a link between the negative affect and defensive behavior cued by reminders of trauma and subsequent emotional-processing dysfunction in PTSD, in men and women with PTSD stemming from service in Vietnam. Special effort will be made to recruit and study Hispanic male veterans with PTSD because this group has been found to be at higher risk for PTSD. Two studies are planned to test various parameters of emotional-processing in PTSD. Study 1 will examine the emotional responses of men and women Vietnam veterans with and without PTSD, under three conditions: a neutral baseline condition, a non-trauma-related stressor condition (a fear film), and a trauma-related prime (war-zone images and sounds). The PTSD groups are expected to exhibit more intense emotional reactions to negatively images only as a result of exposure to the trauma-related prime. The trauma prime should also uniquely suppress positively valenced responses in the PTSD groups. Study 2 is a parametric examination of the threshold of stimulus intensity required to elicit a full range of positive and negative emotion in PTSD. We hypothesize that patients with PTSD are predisposed to require a higher threshold of intensity to elicit positive emotion and a lower threshold for negative affect, and that Hispanic male's with PTSD require a higher threshold for positive and negative emotion. In each study, a variety of psychophysiological indicators of emotional response to standardized emotion eliciting color photographs will be assessed. We pay particular attention to the modulation of startle reflex activity, which has been shown to reliably index the valence of emotional responsivity. In Study 2 we will evaluate the degree of stimulus intensity required to produce startle modulation of positive and negative emotion in PTSD.