P300 SEQUENCE EFFECTS, PROBABILITY, AND INTERSTIMULUS-INTERVAL

Probability and interstimulus interval effects on P3(00) event-related potential(ERP) stimulus sequences were examined in 2 experiments. ERP s were elicited with an auditory-discrimination paradigm in which subj ects were instructed to detect target stimuli from a series of target (T) and standard (S) tones that were varied by randomly presenting 1 o f 4 sequence patterns (SS, TS, TT, ST). Experiment 1 manipulated targe t stimulus probability as either 0.33 or 0.67; Experiment 2 kept targe t probability at 0.33 and manipulated the interstimulus interval (ISI) as either 2 or 6 s. Increases in target stimulus probability produced smaller P300 amplitudes that were additive with stimulus sequence typ e. ISI did not reliably affect P300 amplitude, although ISI interacted with stimulus sequence. P300 latency from the stimulus sequences was influenced weakly by the probability and ISI factors, with few consist ent sequence effects obtained for the N1, P2, and N2 potentials. The r esults suggest that even relatively short sequences can affect P300 am plitude in the same way as longer sequences: as the number of standard stimuli preceding the target increased, P300 amplitude increased. The theoretical implications of the findings are discussed in the context of applied testing situations. (C) 1997 Elsevier Science Inc.