Peak of Tension test in which the critical item, or key, is known only to the investigator, polygraph examiner, a guilty person, or a person with incriminating knowledge. The key is placed in a question series among other items equally plausible to an innocent examinee and presented to the subject to determine if a consistent physiologic arousal occurs to the key. Like all Peak of Tension procedures, trend responses are used in addition to specific responses to interpret the recordings.