The polygraph or "lie detector", whether it is used for criminal investigations or for screening (the latter being the subject of the current NAS panel invstigation--"Polygraph Screening: Panel Seeks Truth in Lie Detection Debate), is a purported application of psychophysiology that, in reality, does not detect lying by either scientific or even common-sense standards.
The polygraph (as it is employed in North America and a few other countries like Israel) is not a "test", because, unlike other psychological tests (e.g., IQ tests) it is not standardized. For example, the examiner makes up some of the questions on the spot during an interview with the examinee. Again, the duration of a polygraph examination can be anywhere from an hour to eight hours, depending on the feelings of the examiner. The "test" is really an unstructured interrogatory psychodynamic interview.
But even if the polygraphic interview were standardized, it would be virtually useless for differentiating the anxious-but-innocent person from the anxious-and-guilty one. So, in the case of screening for spies, a question about spying activity could produce a relatively large autonomic physiological response (e.g., an increase in skin conductance or in blood pressure), but there is no way of knowing whether this large response is due to an innocent person being nervous about the accusation, as against a guilty person being nervous about being caught.
The ancient Romans used to consult priests who read the entrails when they wanted to know the truth, but people like Cicero, in De Divinatione, used common sense to refute the validity of entrails reading. They recognized that truth did not lie in the entrails, but rather had to be established on the basis of valid evidence, and sometimes could not be established for certain at all. It is disturbing not only for Americans, but also the world, that the national security of the world's only remaining super power appears to depend on this modern flight of superstitious technological fancy, the only effect of which is to spread distrust within those organizations that employ it.
John J. Furedy, Professor of Psychology, Unviversity of Toronto.