P300, stimulus intensity, modality, and probability.

Auditory and visual stimulus intensity were manipulated factorially with target probability to assess the influence of these variables on the P300 component of the event-related brain potential (ERP). Increases in stimulus intensity produced reliable increases in P300 amplitude and decreases in peak latency for both modalities that were additive with target stimulus probability effects. Similar, somewhat weaker stimulus intensity effects also were observed for the N100, P200, and N200 components. The findings suggest that stimulus intensity contributes to both P300 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.