Individuals who served in Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF) are reporting histories of traumatic brain injury (TBI) and symptoms associated with post traumatic stress disorder (PTSD). Standard neuropsychological measures are ineffective at distinguishing between TBI and PTSD. This pilot project will examine whether methods from cognitive neuroscience can determine the effects of TBI and/or PTSD on executive function. Executive function includes many aspects of goal-oriented behavior, including the ability to inhibit inappropriate behaviors and thoughts. In the proposed study, the investigators are focusing on inhibitory processing, as it is a core component of executive function. Although both TBI and PTSD compromise executive function and TBI often occurs in the context of a traumatic event, very little research has attempted to disentangle the effects that each of these conditions has on inhibitory control. In addition, the investigators are interested in how disinhibition may be linked to impulsive real-world behaviors, such as suicidal tendencies, which are observed at elevated rates in individuals with TBI as well as those with PTSD. Knowing the ways in which inhibitory functions are compromised in these individuals should aid in the development of appropriate treatments aimed at functional improvement for those with mild TBI, PTSD, or mild TBI+PTSD.