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 .
In a polygraph test monitors that are attached to the subject's body measure physical responses, and little pens attached to the monitors record the responses on a graph. The literal meaning of polygraph is "many writings". Those who favor polygraphs 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 credibility 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 word against that of another.