Target detection studies have been widely applied in the study of cognitive functions, since they have been shown to reflect arousal, attention, stimulus processing and memory operations (Polich and Herbst, 2000). They are performed by means of acoustic, visual or somatosensory oddball tasks, in which the subject responds to target stimuli that occur infrequently and irregularly within a series of standard stimuli. The detection of these task-relevant stimuli is associated in the EEG recordings with the P300 component, a transient activity with latency between 250 and 550 ms (Picton, 1992). The amplitude of the P300 component has been shown to be generally affected, in healthy subjects, by the amount of mental effort and learning, as well as habituation (Lew and Polich, 1993; Polich and Kok, 1995). In addition, although the underlying mechanisms for the abnormal P300 component are unknown, this evoked response has proved to be an important tool in neuropsychiatric research for the investigation of many disorders that influence the central nervous system (CNS) function, including schizophrenia (Blackwood, 2000), Alzheimer's disease (Muscoso et al., 2006), and Parkinson's disease (Katsarou et al., 2004).
