P900: A Putative Novel ERP Component that Indexes Counter-Measure Use in the P300-Based Concealed Information Test

Abstract

Counter-measures pose a serious threat to the effectiveness of the Concealed Information Test (CIT). In a CIT experiment, Rosenfeld and Labkovsky (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 counter-measure 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 counter-measure 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 birth date). 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 counter-measure-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 counter-measures to evade detection.

Keywords: P300, P900, CIT, GKT, counter-measures