The recently released film Professor Marston and the Wonder Women prominently features the use of the polygraph, or lie detector. Dr. William Moulton Marston and his wife Elizabeth, both research psychologists, are credited in the film with having invented the device. Curiously, however, in the movie it is never referred to by it scientific name; it’s only called “the lie detector.”

There may be good reason for this: poly means “many,” so polygraph means “many tracings.” And indeed, we are told in the film that the lie detector, which was already set to measure several physiologic functions, does not work until the Marstons add a measurement of systolic blood pressure. Therefore, the device should be producing a group of simultaneous tracings, as modern polygraphs do. However, we see only a single line which remains flat when the subject is telling the truth, and goes wild when the subject is lying.

If only it were that simple – or that easy to interpret.

The problem with polygraphs is that the tracings must be interpreted by the operator, and those interpretations are based on comparisons with a series of baseline “neutral” questions that the subjects are asked before the test begins. Therefore, there is inevitably a degree of subjectivity introduced, such that different polygraph operators can obtain different results from the same subject. Also, many subjects can train themselves to “fool” the polygraph – there are even articles instructing candidates for executive positions at companies that use the polygraph on just how to fool it.

In a 2004 article titled “The Truth About Lie Detectors (aka Polygraph Tests),” the American Psychological Association stated:

The accuracy (i.e., validity) of polygraph testing has long been controversial. An underlying problem is theoretical: There is no evidence that any pattern of physiological reactions is unique to deception. An honest person may be nervous when answering truthfully and a dishonest person may be non-anxious. Also, there are few good studies that validate the ability of polygraph procedures to detect deception. As Dr. Saxe and Israeli psychologist Gershon Ben-Shahar (1999) note, ‘it may, in fact, be impossible to conduct a proper validity study.’ In real-world situations, it’s very difficult to know what the truth is.

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So while watching that single line on a drum go crazy when Dr. Marston asks his research assistant whether she is in love with him and with Elizabeth may make for a dramatic scene, it bears little if any resemblance to the true nature of polygraphs, which cannot and do not yield such instantaneous, unequivocal results. So, ironically, the lie detector as depicted in Professor Marston and the Wonder Women is itself more lie than truth.

Smithsonian Magazine

Richard Schloss is a Board-Certified psychiatrist in full-time private practice.