The lie detector

The history of the lie detector is a practical reflection of the lack of firm ground in the psychophysiology of emotion. Determining whether someone is being truthful is important in all walks of life. Historically, the methods used have ranged from torture through interrogation to interview. At one time, suspected witches were ducked under water for some time. If they drowned, they were innocent. If they did not drown, they must be witches and so were put to death anyway. There was no way out of this test (what these days we may refer to as a ‘Catch 22’) – but the obvious way to deal with slightly less extreme methods is to tell people what you think they want to hear (that is, to lie but in such a way that it ‘beats’ the test). The rationale behind the lie detector, or polygraph is that the act of lying causes measurable psychophysiological changes in emotional arousal. The polygraph measures such responses as heart rate, blood pressure, respiration and the electrical conductivity of the skin which changes with variations in sweating). Measures are taken from the person when relaxed and again when a mixture of critical and non-critical questions are put: ‘When did you last hold a gun?’ versus ‘When did you last hold a party?’ for example. Similar questions might be asked of an ‘innocent’ person and patterns of response compared. Our psychophysiological responses are thought to give us away but, in practice, polygraph methods of lie detection are not reliable. Merely being asked about a gun might cause changes in psychophysiological measures, and, furthermore, it is very unlikely that there is a particular response pattern for lying (e.g. Lykken, 1984; Saxe, 1991). If a foolproof way to detect lying is ever devised, enormous ethical dilemmas will arise. Imagine taking a lie detector test at a job interview and then being told that you would not beemployed because you had cheated once at school. Imagine parents giving such tests to their children.