The old switcheroo: when target environmental sounds elicit a novelty P3

Objective: Novel environmental sounds that are task-irrelevant in the novelty oddball paradigm elicit the novelty P3 or P3a with a fronto-central scalp distribution, while pure tone task-relevant stimuli elicit a P3 with a posterior topography (P3b). To determine whether stimulus nature or its function in the task modulates scalp topography, the role of the two types of stimuli during the novelty oddball task was reversed. Methods: Brain electrical activity was recorded while 12 young adults listened to frequent tones, infrequent tones, and infrequent environmental sounds. Subjects were not informed about the infrequent tones, but were instructed to press a reaction time (RT) button when they heard the infrequent environmental sounds. Results: Despite the 'novelty' nature of the tones, they were associated with a posterior scalp distribution typical of the P3b. Similarly, despite the 'target' nature of the environmental sounds, they were associated with a fronto-central scalp topography typical of the P3a. Conclusions: These data suggest that the elicitation of a novelty P3 depends not only on task demands but also on the physical nature of the stimulus. Significance: The brain's orienting response is modulated by the contextual environment as well as the physical properties of the eliciting stimulus. (C) 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.