In a polygraph , monitors that are attached to the subject 's body measure physical responses , and little pens attached to the monitors write the responses on a graph . The literal meaning of polygraph is " many writings " . One purpose of this pre-test interview is to reduce the subject's anxiety and fear, and take the surprise out of the allegations. Those who favor this usage say that when people lie anxiety and fear of being caught cause involuntary changes in blood pressure and the way they breath and sweat . Critics say they have little evidence and that it is wrong to equate fear and distress with guilt . The public pays attention to polygraphs when a famous person takes one , usually when it is one person 's testimony against that of another .
In a polygraph , monitors that are attached to the subject 's body measure physical responses , and little pens attached to the monitors write the responses on a graph . The literal meaning of polygraph is " many writings " . Those who favor this usage say that when people lie anxiety and fear of being caught cause involuntary changes in blood pressure and the way they breath and sweat . Critics say they have little evidence and that it is wrong to equate fear and distress with guilt . The public pays attention to polygraphs when a famous person takes one , usually when it is one person 's testimony against that of another .