Beyond the Polygraph: Deception Detection and the Autonomic Nervous System

Procedures

Today’s polygraph builds on these techniques. A standard polygraph measures respiration, heart rate, BP, and sudomotor function (sweating). Respiration is measured via strain gauges strapped around the chest and abdomen that respond to chest expansion during inhalation. BP and pulse can be measured through a variety of means, including finger pulse measurement or sphygmomanometer.⁸

Perspiration is measured by skin electrical conductance. Human sweat contains a variety of cations and anions—mostly sodium and chloride, but also potassium, bicarbonate, and lactate. The presence of these electrolytes alter electrical conduction at the skin surface when sweat is released.¹⁰

The exact questioning procedure used to perform a polygraph examination can vary. The Comparison Question Test is most commonly used. In this format, the interview consists of questions that are relevant to the investigation at hand, interspersed with control questions. The examiner compares the changes in vital signs and skin conduction to the baseline measurements generated during the pretest interview and during control questions.⁸ Using these standardized techniques, some studies have shown accuracy rates between 83% and 95% in controlled settings.⁸ However, studies performed outside of the polygraph community have found very high false positive rates, up to 50% or greater.¹¹

The US Supreme Court has ruled that individual jurisdictions can decide whether or not to admit polygraph evidence in court, and the US Court of Appeals for the Eleventh Circuit has ruled that polygraph results are only admissible if both parties agree to it and are given sufficient notice.^12,13 Currently, New Mexico is the only state that allows polygraph results to be used as evidence without a pretrial agreement; all other states either require such an agreement or forbid the results to be used as evidence.¹⁴

Although rarely used in federal and state courts as evidence, polygraphy is commonly used during investigations and in the hiring process of government agencies. DoD Directive 5210.48 and Instruction 5210.91 enable DoD investigative organizations (eg, Naval Criminal Investigative Service, National Security Agency, US Army Investigational Command) to use polygraph as an aid during investigations into suspected involvement with foreign intelligence, terrorism against the US, mishandling of classified documents, and other serious violations.¹⁵

The Role of the Physician in Polygraph Assessment

It may be rare that the physician is called upon to provide information regarding an individual’s medical condition or related medication use and the effect of these on polygraph results. In such cases, however, the physician must remember the primary fiduciary duty to the patient. Disclosure of medical conditions cannot be made without the patient’s consent, save in very specific situations (eg, Commanding Officer Inquiry, Tarasoff Duty to Protect, etc). It is the polygraph examiner’s responsibility to be aware of potential confounders in a particular examination.¹⁰

Physicians can have a responsibility when in administrative or supervisory positions, to advise security and other officials regarding the fitness for certain duties of candidates with whom there is no physician-patient relationship. This may include an individual’s ability to undergo polygraph examination and the validity of such results. However, when a physician-patient relationship is involved, care must be given to ensure that the patient understands that the relationship is protected both by professional standards and by law and that no information will be shared without the patient’s authorization (aside from those rare exceptions provided by law). Often, a straightforward explanation to the patient of the medical condition and any medication’s potential effects on polygraph results will be sufficient, allowing the patient to report as much as is deemed necessary to the polygraph examiner.