The short answer to that is it cannot, because we’ve got multiple issues here. The first one to start with is what psychologists have called – operationalisation. Huge word, but basically what it means is how do you measure something. So, something like lying, we can define it as not telling the truth – but how do you know what the truth is, is the first question we have to ask ourselves. If you don’t know what the truth is, then you don’t know if someone’s lying. It’s a huge problem.
So, when we think about operationalisation, we are asking to what extent we can design a measurement that is really, really accurate and really, really good at measuring the thing we’re interested in. So in this situation, it’s lying. But, we don’t know what the truth is a lot of the time. So what we need to do is try to indirectly measure the thing that we’re interested in. That’s one way of operationalising lying, and you can do that with something called a polygraph.
A polygraph will measure your physiological responses when speaking about something. The idea being that lying is correlated with, and is associated with bodily experiences of perhaps increased heart rate, or respiration, or getting warmer.
But, it is just an association. Not everyone who’s lying will have that experience. So, the polygraph works, or is supposed to work on the assumption that if we lie, our body responds in a particular way, and we can pick that up. But of course you can see lots of pitfalls in that argument, because perhaps you’re hot because you’re in a hot room. Perhaps you are responding in a certain way because you’ve got a medical condition that makes you respond like that all of the time – regardless of whether you’re telling the truth, or whether you’re lying.
So, really all the polygraph tests can do is tell us about the physiological response. The question is then can we interpret the physiological body response as an indirect measure of lying – and I don’t think you can, at least not all the time.
