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Abstract

INGRAM, E. M. Event-related potentials: The P300 and self- referent stimuli. July 1994, Report No. DoDPI94-R-0006. Department of Defense Polygraph Institute, Ft. McClellan, AL 36205.

This was an exploratory study designed to assess the effect of self-referent stimuli on the P300 component of the electroencephalogram (EEG). The stimuli were self-referent phrases. Self-referent phrases are phrases that are personally descriptive, and are, therefore, considered to be personally relevant. Personal relevance was manipulated through the truthfulness of the self-referent phrases. The EEG was examined for the occurrence of the P300 wave of the human event-related brain potential. The P300 is a positive wave of the EEG that occurs 300 milliseconds after the onset of an eliciting stimulus. The P300 was examined for any effects on its amplitude having to do with the truthfulness of the stimuli. The EEG activity was recorded from 20 male subjects who were presented visual stimuli on a computer monitor. The stimuli consisted of five true and five false self-referent phrases. The two-word phrases were repeatedly presented in random order for a total of 300 presentations (150 presentations of the true and 150 of the false). The probability of occurrence of each of the two classes of stimuli was 0.50. The subjects were required to do nothing except read the stimuli. Results indicate that both true and false self-referent stimuli elicited clearly identifiable P300s. The difference between P300 amplitudes elicited by true and false stimuli, however, was not significant (p > .05).

Key-words: event-related potentials, P300, self-referent stimuli, detection of deception.

Director's Foreword

The sensors used to collect physiologic responses during a psychophysiological detection of deception examination have not changed significantly in over fifty years. The advent of electrical amplifiers and digital computers have improved the quality of the recordings, but the physiologic responses actually measured have not changed significantly.

It is possible that physiologic activity which was not reliably measured twenty, or even ten years ago, could be indicative of deception. Advances in technology now permit the reliable recording and analysis of a variety of new responses. One category of such responses includes the components of the electroencephalogram. These include specific waveforms of electrical activity, measured from the brain, which are generated in response to external events. Reports in the recent scientific literature suggest that electroencephalographic activity changes during cognitive processing. Some reports suggest that deception may be identified using these responses. The current, preliminary, study was undertaken to investigate the use of electroencephalographic measures as indicators of deception.

Michael H. Capps

Director