P300 amplitudes in the concealed information test are less affected by depth of processing than electrodermal responses

Matthias Gamer,Stefan Berti

doi:10.3389/fnhum.2012.00308

Abstract

The Concealed Information Test (CIT) has been used in the laboratory as well as in field applications to detect concealed crime related memories. The presentation of crime relevant details to guilty suspects has been shown to elicit enhanced N200 and P300 amplitudes of the event-related brain potentials (ERPs) as well as greater skin conductance responses (SCRs) as compared to neutral test items. These electrophysiological and electrodermal responses were found to incrementally contribute to the validity of the test, thereby suggesting that these response systems are sensitive to different psychological processes. In the current study, we tested whether depth of processing differentially affects N200, P300, and SCR amplitudes in the CIT. Twenty participants carried out a mock crime and became familiar with central and peripheral crime details. A CIT that was conducted 1 week later revealed that SCR amplitudes were larger for central details although central and peripheral items were remembered equally well in a subsequent explicit memory test. By contrast, P300 amplitudes elicited by crime related details were larger but did not differ significantly between question types. N200 amplitudes did not allow for detecting concealed knowledge in this study. These results indicate that depth of processing might be one factor that differentially affects central and autonomic nervous system responses to concealed information. Such differentiation might be highly relevant for field applications of the CIT.

Highlights

The valid differentiation of offenders and people who are innocent of a crime under investigation is one of the most important issues in forensic sciences
A dissociation was observed between autonomic responses and an explicit memory test: In detail, the results showed larger skin conductance responses (SCRs) to deeply encoded details while no differences were obtained in an explicit memory test
To further examine how the strength of episodic memories relates to physiological responses in the Concealed Information Test (CIT), the current study focused on information that was encoded in the same situation but with varying depth of processing

Summary

Introduction

The valid differentiation of offenders and people who are innocent of a crime under investigation is one of the most important issues in forensic sciences. A method that seems to be widely accepted in the scientific community is the so-called Guilty Knowledge or Concealed Information Test (GKT, CIT; Lykken, 1959; Ben-Shakhar et al, 2002) This method can be regarded as an indirect test for an involvement in a crime since the participant is not asked accusatory questions (e.g., “Did you rob the grocery store last night?”) but instead confronted with a series of questions presented in a multiple choice format that ask for specific details of the crime under investigation (e.g., the weapon that was used for the robbery, the amount of money that was stolen). It is assumed that the recognition of crime related details by a guilty examinee results in enhanced physiological responses as compared to the irrelevant items. Innocent examinees without such knowledge should show a non-systematic response pattern. This general response pattern has been found for a number of different behavioral and physiological measures (for a comprehensive overview see Verschuere et al, 2011)

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Conclusion