Countermeasure Mechanisms and Ecological Validity of P300-Based Concealed Information Tests

This project was competitively awarded in 2012 under the Graduate Research Fellowship solicitation to support dissertation research designed to examine the ecological validity of laboratory P300-based concealed information tests (CIT) and the cognitive mechanisms of countermeasures (CM), which are covert responses a guilty suspect could potentially make in an effort to defeat the test and appear innocent. The CIT is a credibility assessment tool that allows an examiner to determine whether or not a person has knowledge of a crime by asking the suspect a series of questions relevant to the crime to which only a guilty person could know the answers. When presented serially with potential answers to a relevant question, a guilty suspect will recognize the correct alternative (the probe) amongst the incorrect alternatives (irrelevants), which evokes an involuntary physiological response through the endogenous orienting response. Using relatively simple electroencephalography (EEG), this orienting response can be measured through the P300 event-related potential (ERP) and used as a measure of recognition to determine if the suspect is connected to the crime. Current results from an initial study have identified an issue of serious concern for the ecological validity of P300-CITs: potential suspects prior knowledge of crime details. Another study here will examine the cognitive mechanisms involved in P300-CIT countermeasures, specifically whether P300s evoked to countered-irrelevant stimuli are due simply to a simple recognition process. The results from this study will allow identification of the most effective CMs to use in a P300-CIT, and then to apply these methods to test the protocol in an ecologically valid mock crime procedure. ca/ncf