Emitted P300 and slow wave event-related potentials in guessing and detection tasks.

A comparison was made of evoked and emitted P300 and Slow Wave activity elicited in guessing and signal detection tasks. The stimulus conditions were the same in both tasks. Only the instructions to the subjects were different. Latency corrected averaging was used to compensate for trial-to-trial fluctuation of P300 latency. Principal components-varimax analysis (PCVA) was utilized to deal with overlap among P300, Slow Wave and CNV return-to-baseline. Clear measures (from both conventional and latency corrected averages) of emitted P300 components for correct rejection trials were obtained under the following conditions: (a) stimulus intensity near threshold (detection accuracy approximately equal to 78%, d' approximately equal to 1.9); (b) no simultaneous cueing signal; (c) stimulus presence and absence were equiprobable; (d) estimated contributions of overlap from other event-related potential components were removed from the P300 measurements. A significant difference was found between the Slow Wave topographic profiles elicited in the guessing and detection tasks. For the guessing task Slow Wave was relatively large and positive at vertex whereas in the detection task it was near zero amplitude at vertex. No significant differences due to task were found for the P300s when a PCVA derived estimate of the contribution of Slow Wave overlap was removed from the P300 measures.