When we lie, our blood pressure goes up, our heart beats faster, we breathe more quickly (and our breathing slows once the lie has been told), and changes take place in our skin moisture. A polygraph charts these reactions with pens on a moving strip of graph paper. . . . The result is jagged lines that don't convey a lot to you. But . . . an examiner can tell from those mechanical scribbles whether or not you've spoken the truth.
-- CHRIS GUGAS, polygrapher, The Silent Witness, 1979
The widespread use of polygraphic interrogation methods is not based on public acceptance of the idea that polygraphers are better human lie detectors than are judges or juries or personnel interviewers or, indeed, than people in general. Suppose that, in a criminal trial, the prosecution called to the stand Mr. Reid or Dr. Larson or Father Summers and sought to have any one of them accredited as an expert witness without benefit of the polygraph:
Your honor, Mr. Reid has many years of experience in interrogating criminal suspects. He has spent two hours interviewing this defendant. He has reviewed the case facts, heard the defendant's alibi, asked him various searching questions, and closely observed his demeanor and behavior. As an expert in the diagnosis of deception, Mr. Reid is prepared to testify that, in his expert opinion, this defendant is lying when he denies his guilt in the present matter.