Countering information leakage in the Concealed Information Test: The effects of item detailedness

Concealed Information Tests (CIT) are administered to verify whether suspects recognize certain features from a crime. Whenever it is presumed that innocent suspects were contaminated with critical information (e.g., the perpetrator had a knife), the examiner may ask more detailed questions (e.g., specific types of knives) to prevent false positives. However, this may increase the number of false negatives if the true perpetrator fails to discern specific details from its plausible irrelevant controls, or because detailed crime‐scene information may be forgotten. We examined whether presenting items at the exemplar level protects against contamination, and whether it compromises the sensitivity in a physiological CIT. Participants (N = 142) planned a mock‐robbery, with critical items encoded either at the category or at the exemplar level. The CIT was administered immediately or after a 1‐week‐delay, with questions phrased at the categorical or exemplar level. There were no effects of time delay. Results revealed that when item detailedness was congruent at encoding and testing, the SCR, HR, and RLL showed larger differential responses, as compared with incongruent conditions. Participants contaminated with crime knowledge at the categorical level did not show a CIT‐effect for crime details at the exemplar level, suggesting detailed questions may counter the leakage problem. Asking questions at the exemplar level did not reduce the CIT detection efficiency as compared to asking questions at the categorical level. The importance of congruency between encoding and testing provides examiners with a challenge, as it is difficult to estimate how details are naturally encoded.