While the reading passage appraises the accuracy of the polygraph high, the lecturer does not agree with that the polygraph is perceived as a "lie-detector." According to the lecturer, the polygraph simply provides the information of the physiological changes, not the conclusion whether an examinee lies or not.
The first point made by the lecturer is the possibility that the change of various physical conditions comes from the stress out of the test, not from the lie. The one under the test can change his heart rate, and perspiration due to the anxiety of the test. This casts doubts on the reading passage's claim that these body signals simply mean that the examinee is lying.
Secondly, the lecturer also provides the fact that people can lie to the instrument by controling their body response. For instances, some of examinees took pills to tranquilze themselves and spread anti-perspirant on their hands. Furthermore, it is reported that some people even stabbed their feet on tacks hid in their shoes in order to make their responses equal. This also tosses the question toward the reading passage's description that it is impossible to deceive the machinery because the responses are involuntary.
Final point mentioned by the lecturer is the influence of the examiner. Because there are only two people in the test room, the examinee and the examiner, the small actions of the examiner can affect the test result. For example, untrained examiners are declined to raise the possibility of unfavorable results for examinees. This point is what the reading passage also misses.
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