Systematic changes in tonic physiological activities during the Concealed Information Test

• We analyzed pre-stimulus physiological levels in the Concealed Information Test.
• Skin conductance, heart rate, and normalized pulse volume were recorded.
• Serial position of a relevant item affected changes in pre-stimulus levels.
• Vascular tone increased until relevant item presentation.

Many studies on the Concealed Information Test have focused on phasic physiological changes that are temporally 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.