Systematic changes in tonic physiological activities during the Concealed Information Test Tokihiro Ogawa a, ⁎, Izumi Matsuda a , Akihisa Hirota b , Noriyoshi Takasawa c a National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan b Faculty of Child Studies, Kamakura Women's University, 6-1-3 Ofuna, Kamakura, Kanagawa 247-8512, Japan c College of Sociology, Edogawa University, 4-7-4 Komaki, Nagareyama, Chiba 270-0198, Japan abstract article info Article history: Received 28 April 2014 Received in revised form 15 August 2014 Accepted 17 August 2014 Available online 21 August 2014 Keywords: Concealed Information Test Tonic physiological level Orienting response Many studies on the Concealed Information Test have focused on phasic physiological changes that are tempo- rally locked to stimulus presentation. However, little is known about changes in tonic, basal physiological levels throughout a stimulus series. This study focused on changes in tonic physiological activities during the CIT. Thirty-nine participants carried out a mock theft and subsequently received a CIT. Skin conductance, heart rate, and normalized pulse volume (NPV) were recorded. The pre-stimulus physiological level of these measures throughout the CIT series was compared across a question series with different serial positions of the relevant item. Results showed that changes in the pre-stimulus level differed depending on the serial position of the relevant item. Skin conductance declined throughout the series, but showed a transient increase after relevant item presentation. Heart rate was relatively constant throughout the series, but decreased after relevant item presentation. NPV continued to decrease until the relevant item, but increased thereafter, indicating a pattern similar to the classic Peak of Tension concept. In addition, the pre-stimulus NPV showed a significant relevant– irrelevant difference. Theoretical and practical implications of these findings are discussed. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Concealed Information Test (CIT; also known as the Guilty Knowledge Test), is a method of psychophysiological information detection used in criminal investigation (Lykken, 1959, 1960) to exam- ine whether an examinee knows a certain detail of a crime that could only be known to a person involved in the crime. In the CIT, a polygraph examiner prepares several questions about criminal details. Each question consists of one crime-relevant item (i.e., a feature of the crime under investigation) and several crime-irrelevant items. Questions are constructed so that an individual with no information about the criminal fact would be unable to distinguish the relevant item from the irrelevant items. While sequentially presenting these items, several phasic, stimulus-locked physiological changes such as skin conductance response (SCR) and heart rate (HR) deceleration are examined (Lykken, 1959; Bradley and Janisse, 1981). If the examinee differentially responds to the relevant item (e.g., larger SCR and deceler- ation of HR), then knowledge about that criminal fact is inferred. This differential responding to the relevant item has been explained as an en- hanced orienting response (OR) because the relevant item is significant only to a person possessing knowledge of the crime (Lykken, 1974). While the CIT literature has focused on phasic, stimulus-locked phys- iological changes such as SCR and HR deceleration, changes in tonic, basal levels of physiological activities have received little attention. Tonic activity refers to the slower, long-term changes in background physiological levels. For example, Hira and Furumitsu (2009) compared the tonic level of HR and respiration rate during the CIT between guilty and innocent examinees. They analyzed these measures in arbitrarily se- lected periods of 1 min from the first and the last question of the CIT. The authors found that innocent persons showed a lower HR compared with guilty persons, and revealed a significant decrease over the course of the test, whereas guilty persons maintained a constant HR level. In the OR literature, on the other hand, pre-stimulus physiological level at each stimulus presentation often serves as a measure of tonic activities (Barry and Sokolov, 1993; Rushby and Barry, 2007). The present study also analyzed within individual variations at a pre-stimulus physiologi- cal level throughout a question series. If CIT examinees concealing information show systematic changes in pre-stimulus levels during the test, such changes would provide useful information that could be used to determine whether an examinee is concealing information. The idea that CIT examinees concealing information would show systematic tonic changes is not novel, but remains to be empirically established. For example, the classic Peak of Tension (POT) test assumes International Journal of Psychophysiology 94 (2014) 455–462 Abbreviations: ANOVA, analysis of variance; CIT, Concealed Information Test; HR, heart rate; NPV, normalized pulse volume; pHR, phasic heart rate; pNPV, phasic normalized pulse volume; POT, Peak of Tension; SCL, skin conductance level; SCR, skin conductance response. ⁎ Corresponding author. Tel.: +81 4 7135 8001. E-mail address: t-ogawa@nrips.go.jp (T. Ogawa). http://dx.doi.org/10.1016/j.ijpsycho.2014.08.584 0167-8760/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Psychophysiology journal homepage: www.elsevier.com/locate/ijpsycho