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Retrieval of information from memory takes place for two different processing requirements. One for recognition of the entities of the external world, which must happen rapidly as the individual’s efficiency to deal with the world depends on quick detection of the changes in the world. The other retrieval is related to remembrance of autobiographical episodes, which are experiences of the individual. Several studies have shown the involvement of different neural structures during the activation of the two retrieval processes. The process of recognition of an external stimulus is associated with several signal-processing stages viz., sensory registration, arousal of attention followed by detection of the stimulus.
The neurocognitive processes are best represented by electrophysiological changes in the brain, which can be easily recorded using surface electrodes placed on the head (Mukundan, 1986a, 1986b, 1995; Khanna et al., 1989; Mukundan et al., 1989, 1990). Of these stages, the detection or recognition of the stimulus is accompanied by the P300 event related potential (Donchin, 1981; Neville et al., 1986; Donchin and Coles, 1988; Annet & Mukundan, 1996; Mukundan & Rohrbaugh, 1998; Sudha & Mukundan, 1998; Mukundan et al., 1999; Silva et al., 2007). However, the P300 response can be produced only presentation of a brief stimulus lasting not more than 200 ms. The P300 response represents the detection or recognition of a new stimulus and the amplitude of the potential is a function of the special or change in the meaning, unexpected familiarity, or novelty in the stimulus. The P300 potential can be produced by the infrequent stimulus in an oddball paradigm consisting of two stimuli one frequently and the other infrequently presented, every stimulus when a set of different stimuli (Mukundan & Rohrbaugh, 1998) are presented one after the other, or when the same stimulus is presented with varying intertrial interval (Gonsalvez et al., 1995, 1999, 2002, 2007; Mertens & Polich, 1997; Polich & Heine, 1996; Polich et al., 1994).