Lie Detection

The Truths About Lie Detection

The truth is that we do not have a fool-proof way of detecting lies yet. Yes, read that right. That is still science-fiction. We do have had advances though, especially in Psychology and Medicine, but the thing is that lying just involves a lot of factors and expresses itself in many different ways in a person, both internally and externally. Let’s delve into it a bit.

The polygraph

The polygraph was the first technology used to try to find out whether someone is telling the truth or not. It is called a “poly”graph because it takes many different data about your body at the same time, such as blood pressure, respiration rate, pulse, and even stuff like skin conductivity, and puts them all into the same graph.

As you may have guessed, if someone becomes nervous during an interview or interrogation, the graphs will spike: pulse, respiration and blood pressure increase, as the heart starts pumping more blood (classic fight or flight response) and the skin becomes more conductive because of sweat (it is a saline solution, so it is more conductive).

But that is it. It displays physiological changes. Not everyone that is nervous is lying, and not everyone that lies will become nervous while doing so. It will all depend on context and other evidence along with the graph in order to know what is a lie and what isn’t, so may as well just use the evidence themselves, as they are more reliable.


If you have watched “Lie To Me” you already know what this is about. It is the analysis of a person’s split-second non-verbal expressions, along with the usual verbal and non-verbal expressions. These microexpressions tend to arise when we are faced with some kind of internal conflict. It is basically our body betraying our brain in ways we don’t even notice.

Microexpressions are basically the opposite of the polygraph. While the polygraph uses measurable and objective data, microexpressions rely much more on the interrogator’s knowledge and intuition at the moment. That is not to say it is objectively worse: microexpressions can’t be caught by the polygraphy. We just can’t measure that kind of change in human physiology. It would be indistinguishable from the usual noise. That does mean that they perfect though.

What is the problem?

The thing is, both of those methods can be fooled by good enough acting and emotional intelligence. You just have to convince yourself that the lie is the truth and the truth is the lie. The polygraph may be able to catch the bad liar, and analysis of microexpressions may catch the good liar, but they can’t deal with the best liars out there, and they are the main problem.

Torture is another thing that is out of the question, and in the end it is mostly a waste of time and a kind of power fantasy. If someone really wants to hide something, they’ll do it regardless of the circumstances. Sure, you can get information from the underlings, but they also won’t have the critical information you are looking for.

There is also no such thing as a “truth serum”, and if someone is trying to convince you to get something like that, you can be sure that they are lying. Most of the substances people call “truth serums” are actually drugs of many kinds, like hallucinogens and anesthetics, including weed and alcohol believe it or not. There is no guarantee that someone will be truthful after taking it. There are even good chances that they may come up with some kind of delusion and become convinced that they are truer than the truth.

There are some techniques being tested to try to settle this problem once and for, but don’t get your hopes up. One of them consists on using MRI scans. So it can end up being a bit expensive. For now, it is best to rely on good old evidence and logic. They are much more reliable than people anyway.