Increasing the ERP signal in the detection of guilty knowledge

The N400 and P300, two event-related potentials (ERPs), were tested using a modified Guilty Knowledge Test for their effectiveness in discriminating people possessing guilty knowledge from those who did not. In the study phase, participants read different passages that detailed either a crime in a specific location (Guilty), some location, without a crime (Innocent but Knowledgeable) or an unrelated location without a crime (Naive). During EEG collection, participants viewed context phrases, some of which were relevant to the crime scene, and test words that were either congruent or incongruent to the context phrases. In Experiment 1, both Guilty and Innocent but Knowledgeable participants were originally classified as guilty because both produced large P300 amplitudes to the crimerelevant stimuli. However, few Innocent but Knowledgeable participants produced significant N400 amplitudes and thus were rejected as guilty in the final analysis. In Experiment 2, participants were assigned to either the Guilty or Innocent but Knowledgeable condition. Seventy-two hours after reading the appropriate passage, participants were divided into two groups: those reminded of the passage read earlier and those who were not. There was not effect of reminding Guilty participants on the discrimination but a strong effect on the Innocent but Knowledgeable participants suggesting a possible technique for discriminating guilty knowledge from other knowledge formats.