P300 has been intensively investigated as an electrophysiological index of cognitive function since its discovery by Sutton et al. [10]. P300 amplitude and latency were used as indices of the nature and timing of cognitive response to a stimulus. Many hypothetical constructs have been suggested to account for the variations in P300 related to attentiveness, orientation, decision making, uncertainty reduction, intentional engagement, demand processing, salience, task relevance, equivocation, and value [11]. The amplitude of the P300 component is multiplied by subjective probability factors and the task relevance of eliciting events, whereas its latency depends on the duration of stimulus evaluation and is assumed to index stimulus processing speed [12]. The oddball task is thought to reflect working memory function and/or attention, and the “updating theory” as an explanation of P300 proposed that P300 is a manifestation of activity occurring when one’s model of the environment must be revised [13]. P300 is thought to be composed of several parts that reflect an information processing cascade when attentional and memory mechanisms are engaged [4]. Since P300 abnormalities in patients with schizophrenia were
