Most studies investigating electrophysiological deficits in alcoholics have focused on the P300 or P3 component. The P3 is a large positive component that occurs between 300 and 700 ms after a “significant” stimulus and is not related to the physical features of the stimulus (e.g., brightness and shape for visual stimuli, or loudness and pitch for auditory stimuli). A stimulus can be “significant” by being relevant to a task (e.g., the subject must press a button whenever a specific stimulus, such as a blue triangle, occurs), by having a motivating influence (e.g., the subject wins money after responding to the stimulus correctly), or by occurring rarely or unpredictably. The P3 is thought to reflect aspects of working memory, the temporary storage of information required for complex cognitive tasks such as learning, reasoning, and comprehension. Specifically, P3 may reflect attention allocation and updating processes (Polich and Herbst 2000). P3 also is thought to reflect cognitive closure, or the termination of a mental process (Desmedt 1980; Verleger 1988), which involves inhibition over widespread cortical areas (Desmedt 1980; Verleger 1988; Rockstroh et al.
