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SYFY WIRE Jim Carrey

Polygraphs and truth serums: The science behind 'Liar Liar'

Obviously, a birthday wish isn't a realistic way to force somebody to tell the truth, but are there ways to stop lying? 

By Cassidy Ward
Jim Carey in Liar Liar (1997)

The beloved 1997 Jim Carrey comedy Liar Liar (now streaming on Peacock) follows the exploits of the titular liar, career attorney, and bad father Fletcher Reede. After yet another disappointment, Fletcher’s son Max spends his one and only birthday wish hoping that for a single day, his father couldn’t tell a lie. Through mysterious forces which are implied but not explained, the wish comes true. For the next 24 hours, Fletcher can’t lie. The consequences of that wish ripple out into his personal and professional life and, along the way, we all learn a valuable lesson.

That lesson, of course, is that lying can be both good and bad. Obfuscating the truth is a power we all have and it’s one we should wield with care. The same can be said about the truth, as well. The right truth in the wrong hands can be a terrible thing. Luckily, birthday wishes can’t stop you from lying, but is there anything that can?


Before we look into whether it's possible to stop somebody from lying, let's examine if it's even possible to determine whether or not somebody is lying. Like most things in science, the birth of the polygraph — commonly known as a lie detector — didn’t happen all at once.

In 1914, Vittorio Benussi published his findings that respiratory activity was impacted by deception. A year later, an American lawyer and psychologist named William M. Marston developed the discontinuous systolic blood pressure test with a similar philosophy in mind. The idea was that lying had some effect on blood pressure and that could be interpreted by measuring those changes over time. In 1921, John Larson combined those two ideas into a single machine that measured blood pressure, heart rate, and respiration with the aim of sorting the truth from lies.

In 1923, only two years after the polygraph was invented, William Marston — you remember him from the blood pressure test above — attempted to use the results of a polygraph as evidence in an actual court case. The judge threw out the polygraph results, noting that while the court was open to experimental evidence, that evidence needed to be based upon established and widely accepted science. Polygraphs failed that test in 1923 — and they still fail it today.

Polygraph machine

Polygraphs largely attempt to infer deception by comparing a person’s physiological response to different questions. The idea is that if you’re hiding something, you’ll have a noticeable physiological response that will be markedly different from the way you behave when telling the truth. Even if that’s true, and it’s unclear whether it is, polygraphs run into a fundamental problem. That there are no universal physiological responses to deception. A truthful person could exhibit the same physical response, and thereby the same polygraph reading, as a deceptive person for any number of reasons, not least of which is nervousness at being given a polygraph.


All right, if we can’t tell when someone is lying then can we force them to tell the truth?

So-called truth serums have been around since ancient times, and you’ve probably taken one yourself. For centuries, alcohol was the truth serum du jour, owing to its ability to lower inhibitions. There’s an old saying you’ve probably heard some variation of that says a drunk mind speaks a sober heart. The idea being that alcohol removes some barrier and unleashes your true self.

While some believe there’s truth to that sentiment, and you’ve maybe even experienced those effects yourself, plenty of folks have found the opposite to be true. How many of us have a horror story about something we said or did, something totally outside of our character, after a couple drinks too many? That’s the trouble with alcohol as a truth serum. While lowered inhibitions might make you more willing to do something you’ve always wanted to do, they also make you more likely to do something you would never do. And there’s no telling which of those two results will occur.

In the early 20th century, a physician named Robert House found the next big thing in supposed truth serums when he used scopolamine, an anesthetic, on his patients and found that they began volunteering information. He believed he had stumbled upon a truth serum.

Interrogation room

In 1922, that claim was put to the test when two men convicted of murder volunteered to be given scopolamine to prove their innocence. While under the influence of the drug, both men maintained their innocence. One of them said afterward, “After I had regained consciousness I began to realize that at times during the experiment I had a desire to answer any question that I could hear, and it seemed that when a question was asked my mind would center upon the true facts of the answer and I would speak voluntarily, without any strength of will to manufacture an answer.”

That more or less sealed the deal in Dr. House’s mind, but the truth was more complicated, as it almost always is. The effect, it turns out, comes from depressing communication between different parts of your nervous system. In essence, everything including thinking becomes a little more difficult to do.

It’s true that telling the truth is cognitively easier than lying, it doesn’t require that you spin a tale on the fly and then remember it later, and people are probably more likely to tell the truth under the influence of scopolamine or sodium pentothal. But they’re also more likely to say something entirely invented just because they think it’s what you want to hear. These compounds have all of the same problems as alcohol. They give you the truth and they give you lies and there’s no good way to sort them out. At least, not yet.

That’s the rub. What we’ve learned is that there are chemicals capable of changing the way we interact with the truth. It’s almost like we’ve found the right buttons to push but not the right sequence, so we’re getting mixed results. If anyone ever figures out the Konami code of lying, all bets are off. Better get busy lying while the lying’s still good.

Just don’t break promises to your kid, Liar Liar could always do with a modern retelling. In the meantime, it’s streaming on Peacock.