P300 response under active and passive attentional states and uni- and bimodality stimulus presentation conditions.

P300 evoked potential patterns were evaluated for two active and two passive attentional states in which stimuli were presented in either one or two sensory modalities. Latency to an infrequent auditory tone was shortest when counting the frequent stimulus, longer when counting the infrequent stimulus, longer still under a passive condition, and longest in a non-P300 condition. P300 amplitudes identifiable in the passive attentional state were enhanced when stimuli were from two, rather than from one, sensory modality. Implications for understanding the mechanism of attention are discussed. Preliminary findings in traumatic brain injury patients suggest that passive P300 responses may be useful in assessing the extent and severity of brain dysfunction.