John B. Meixner

Countermeasures pose a serious threat to the effectiveness of the Concealed Information Test (CIT). In a CIT experiment, Rosenfeld and Labkovsky in Psychophysiology 47(6):1002–1010, ( 2010 ) observed a previously unknown positive ERP component at about 900 ms post-stimulus at Fz and Cz that could potentially serve as an index of countermeasure use. Here, we explored the hypothesis that this component, termed P900, occurs in response to a signal that no further specific response is required in a trial, and could thus appear in countermeasure users that respond differentially depending on the stimulus that appears. In the present experiments, subjects viewed four non-meaningful (irrelevant) dates and one oddball date. In three experiments, we examined P900’s antecedent conditions. In the first, the unique item was a personally relevant oddball (the subject’s birthdate). In a second, the unique item was a non-personally relevant oddball (an irrelevant date in a unique font color). In a third, all dates were irrelevant. We speculated that the presence of an oddball would not be necessary for P900. All participants made countermeasure-like responses following two specific irrelevant dates. As hypothesized, P900s were seen to non-responded-to irrelevant and oddball stimuli in all subjects but not to responded-to irrelevant stimuli, and the presence of an oddball was not necessary for elicitation of P900. This finding has potential application in deception settings—the presence of a P300 accompanied by the presence of a P900 in response to non-countered stimuli could provide evidence of incriminating knowledge accompanied by the attempt to use countermeasures to evade detection.

Previous studies examining the P300‐based concealed information test typically tested for mock crime or autobiographical details, but no studies have used this test in a counterterrorism scenario. Subjects in the present study covertly planned a mock terrorist attack on a major city. They were then given three separate blocks of concealed information testing, examining for knowledge of the location, method, and date of the planned terrorist attack, using the Complex Trial Protocol (Rosenfeld et al., 2008). With prior knowledge of the probe items, we detected 12/12 guilty subjects as having knowledge of the planned terrorist attack with no false positives among 12 innocent subjects. Additionally, we were able to identify 10/12 subjects and among them 20/30 crime‐related details with no false positives using restricted a priori knowledge of the crime details, suggesting that the protocol could potentially identify future terrorist activity.

We recently introduced an accurate and countermeasure (CM)-resistant P300-based deception detection test (J.P. Rosenfeld et al., 2008). When subjects use CMs to all irrelevant items in the test, the probe P300 is increased rather than reduced, as in previous P300-based deception protocols, allowing detection of CM users. Evidence herein suggests this is partly due to an omit effect; the probe was the only uncountered item. Three groups were tested: a guilty omit probe group performed an explicit response to each irrelevant item but not to the probe, an innocent omit irrelevant group saw only irrelevant items and omitted a response to one item, and a guilty no omit group had a concealed information item as probe and performed an explicit response to each. We found a greater P300 amplitude to probes in the guilty omit probe condition as compared with the other two conditions, indicating a P300 enhancing effect of omitting a response to a single stimulus.

We recently introduced an accurate and countermeasure resistant P300-based deception detection test called the complex trial protocol (Rosenfeld et al. in Psychophysiology 45(6):906–919, 2008). When subjects use countermeasures to all irrelevant items in the test, the probe P300 is increased rather than reduced (as it was in previous P300-based deception protocols), allowing detection of countermeasure users. The current experiment examines the role of task demand on the complex trial protocol by forcing the subject to make countermeasure-like response to stimuli. Subjects made either a simple random button response to both probe and irrelevant stimuli (experiment 1) or a more complex, assigned, button response to probe and irrelevant stimuli (experiment 2). We found that an increase in task demand reduced the effectiveness of the test. Using random responses we found a simple guilty hit rate of 11/12 with no false positives, but only a 4/11 hit rate for countermeasure-users. Using assigned responses we found a simple guilty hit rate of 8/15 with no false positives, and a 7/16 hit rate for countermeasure-users. We herein suggest that the high level of task demand associated with these countermeasure-like responses causes reduced hit rates.