P300 habituation from visual stimuli?

The P3(00) event-related brain potential (ERP) was elicited with visual stimuli using an oddball task in which the subject indicated with a finger tap response the occurrence of a target stimulus that occurred randomly on 20% of the trials and refrained from responding to a standard stimulus. A total of six trial blocks were collected, with an equal number of artifact-free epochs averaged for both stimulus types. P3 amplitude from the target stimuli did not decrease across trial blocks; P3 amplitude from the standard stimuli did decrease across trial blocks. P3 latency from both the target and standard stimuli increased across trial blocks. No changes in amplitude or latency independent of the P3 effects were obtained for the other ERP components with trial block. The results suggest that P3 components elicited by visual stimuli do not readily habituate for actively discriminated target stimuli. The theoretical implications are discussed in the context of previous findings.