The Polygraph

The polygraph can be used for purposes other than the evaluation of veracity. For example, it may be used as an adjunct in testing the range of languages spoken by an interrogatee or his sophistication in intelligence matters, for rapid screening to determine broad areas of knowledgeability, and as an aid in the psychological assessment of sources. Its primary function in a counterintelligence interrogation, however, is to provide a further means of testing for deception or withholding.

A resistant source suspected of association with a hostile clandestine organization should be tested polygraphically at least once. Several examinations may be needed. As a general rule, the polygraph should not be employed as a measure of last resort. More reliable readings will be obtained if the instrument is used before the subject has been placed under intense pressure, whether such pressure is coercive or not. Sufficient information for the purpose is normally available after screening and one or two interrogation sessions.

Although the polygraph has been a valuable aid, no interrogator should feel that it can carry his responsibility for him. [approx. 7 lines deleted] (9)

The best results are obtained when the CI interrogator and the polygraph operator work closely together in laying the groundwork for technical examination. The operator needs all available information about the personality of the source, as well as the operational background and reasons for suspicion. The CI interrogator in turn can cooperate more effectively and can fit the results of technical examination more accurately into the totality of his findings if he has a basic comprehension of the instrument and its workings.

The following discussion is based upon R.C. Davis' "Physiological Responses as a Means of Evaluating Information."(7) Although improvements appear to be in the offing, the instrument in widespread use today measures breathing, systolic blood pressure, and galvanic skin response (GSR). "One drawback in the use of respiration as an indicator," according to Davis, "is its susceptibility to voluntary control." 

Moreover, if the source "knows that changes in breathing will disturb all physiologic variables under control of the autonomic division of the nervous system, and possibly even some others, a certain amount of cooperation or a certain degree of ignorance is required for lie detection by physiologic methods to work." In general, "... breathing during deception is shallower and slower than in truth telling... the inhibition of breathing seems rather characteristic of anticipation of a stimulus."

The measurement of systolic blood pressure provides a reading on a phenomenon not usually subject to voluntary control. The pressure "... will typically rise by a few millimeters of mercury in response to a question, whether it is answered truthfully or not. The evidence is that the rise will generally be greater when (the subject) is lying." However, discrimination between truth-telling and lying on the basis of both breathing and blood pressure "... is poor (almost nil) in the early part of the sitting and improves to a high point later."

The galvanic skin response is one of the most easily triggered reactions, but recovery after the reaction is slow, and "... in a routine examination the next question is likely to be introduced before recovery is complete. Partly because of this fact there is an adapting trend in the GSR with stimuli repeated every few minutes the response gets smaller, other things being equal."

Davis examines three theories regarding the polygraph. The conditional response theory holds that the subject reacts to questions that strike sensitive areas, regardless of whether he is telling the truth or not. Experimentation has not substantiated this theory. The theory of conflict presumes that a large physiologic disturbance occurs when the subject is caught between his habitual inclination to tell the truth and his strong desire not to divulge a certain set of facts. Davis suggests that if this concept is valid, it holds only if the conflict is intense. 

The threat-of-punishment theory maintains that a large physiologic response accompanies lying because the subject fears the consequence of failing to deceive. "In common language it might be said that he fails to deceive the machine operator for the very reason that he fears he will fail. The 'fear' would be the very reaction detected." This third theory is more widely held than the other two. Interrogators should note the inference that a resistant source who does not fear that detection of lying will result in a punishment of which he is afraid would not, according to this theory, produce significant responses.