P300: A comparison of active and passive protocols

This study compares the P300 event related potential (ERP) generated by two different stimuli in two different paradigms. ERPs were collected from twenty subjects using both a passive oddball paradigm and an active three stimulus novel paradigm. In both paradigms, a 500 Hz, 100 msec tone was used as the standard. Two different rare stimuli were used: a 1500 Hz, 100 msec tone; and 100 msec novel synthesized sounds (all different). In the three stimulus novel paradigm, both rare stimuli were used. The subject was instructed to count the target 1500 Hz tone and ignore all other sounds. For the passive oddball paradigm, each of the rare stimuli was used with two separate attention controls, a reading control and a thinking control, a total of four separate passive oddball conditions. Each of the five experimental conditions was run twice in order to evaluate possible effects of habituation. The entire experiment was repeated on a second day to determine replicability.;Novel stimuli elicited a significantly larger P300 response than 1500 Hz tones, regardless of paradigm. There was no significant difference between the reading and thinking conditions; both suppressed the amplitude of the ERPs in the passive conditions compared to the attended three stimulus conditions. There was no evidence of habituation of the P300 response to either the 1500 Hz tones or the novels in either the passive or the three stimulus paradigm. The P300 response in the passive oddball paradigm was equally distributed across the midline scalp. The P300 response to both targets and novels in the three stimulus paradigm was parietal maximum.;The significantly larger amplitude P300 response produced by the novel sounds makes it a much better stimulus choice for use in clinical situations in which subject cooperation cannot be assured. The different topography of the responses is discussed in relation to previous P300 studies using both passive and active oddball paradigms and the three stimulus novel paradigm.