This study examined the influence of swallowing as a physical countermeasure (PCM) on heart rate (HR) acceleration in the Concealed Information Test (CIT). In block 1 of experiment 1, pure tones (900 Hz, 75 dB) were first presented to fourteen participants who were subsequently instructed to swallow their saliva after answering “no” or remaining silent. They showed increase in HR and skin conductance response (SCR) as well as a decrease in normalized pulse volume (NPV), but no changes in respiration speed (RS). In block 2, the CIT was conducted with card numbers 3, 4, 5, 6, and 7. In this test, participants were asked to swallow only when a particular noncritical item (swallowing item) was presented. They showed respiratory inhibition, an increase in SCR, and decreases in HR and NPV for the critical items as well as significant HR acceleration in the swallowing items. In experiment 2, ten participants were asked to swallow their saliva after they answered all the questions; they showed HR acceleration, respiratory inhibition, an increase in SCR, and a decrease in NPV for the critical items. These results indicate that swallowing as a PCM will cause HR acceleration in the CIT.
