The effect of change in a stimulus sequence on P300

In past studies, the P300 amplitude of the ERP has been found to be enhanced for infrequent, unpredictable and/or task-relevant eliciting events. A fourth factor, namely the physical change between two consecutive stimuli in event sequences used, has often been confounded with frequency, predictability and relevance. The current study examined whether change also increases the P300 amplitude. Fourteen adults viewed sequences of slides in which predictability, task (counting) and change varied within subject. ERP was recorded at Cz, Pz, Oz and Fz. P300 amplitudes were significantly larger: (1) for unpredictable than for predictable events, (2) for counted than for non-counted stimuli, and (3) for stimulus change rather than no stimulus change. The change effect interacting with counting suggested that P300 amplitude may be particularly increased by stimulus changes imbedded within only certain cognitive tasks.