Your body exhibits subtle physiological changes when you engage in self-deception

A recent study published in the journal Psychophysiology suggests that when people are unsure about their own performance but try to boast about it, their bodies still show subtle signs of lying. The research provides evidence that uncertainty pushes individuals into a middle ground between honesty and deception. This middle ground allows individuals to boost their self-esteem while experiencing less physiological stress than an outright lie.

Humans often navigate complex social situations by deciding whether to be honest or to bend the truth for personal gain. Telling a clear lie usually triggers physical changes like increased sweating, while being completely honest tends to keep the body in a calmer state. Both of these actions depend on a person knowing the actual facts of a situation.

Yet, everyday life is full of ambiguous situations where people do not have all the facts. Scientists wanted to understand what happens to a person’s body and confidence when they lack clear information but still try to present themselves in the best possible light. They aimed to see if people respond to uncertainty by acting as if they are telling the truth, or if their bodies react as though they are actively deceiving someone.

“In our lab, we always like to remind ourselves that humans are social creatures, defined by a strong desire to belong and be acknowledged by others. We decided to delve into this topic because we were interested in exploring how individuals use deception to enhance how others perceive their persona,” explained study authors Giulia Romano Cappi and Olga Dal Monte of the University of Turin.

The researchers recruited 32 healthy volunteers in Italy. The sample included 17 females and 15 males, ranging in age from 19 to 32 years old. In the laboratory setting, each participant sat at a computer across from an actor who was introduced as an expert in lie detection.

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During the experiment, participants completed a series of logical puzzles on the computer. After finishing, they guessed how well they did, choosing whether they performed among the worst or among the best. The computer then provided them with randomly generated feedback about their score.

This feedback created three different conditions for the experiment. In the truth condition, the computer told participants they definitely scored among the best. In the deception condition, the computer told them they definitely scored among the worst.

A third scenario served as the uncertainty condition. Here, the feedback was vague, stating the participant probably performed among the best or probably performed among the worst. This left the participants without a definitive answer about their actual abilities.

Regardless of the feedback they received, participants were instructed to convince the lie detection expert that they had achieved a top score. They were required to answer yes to a series of questions from the expert, culminating in a final question about whether they believed they were among the top performers. To increase motivation, scientists told the participants that their persuasiveness and task speed could earn them a prize.

Throughout this interaction, researchers tracked the participants using specialized sensors. They measured skin conductance, which tracks minute changes in sweat gland activity to determine physiological arousal and stress. After each round, participants rated their own confidence in how well they convinced the expert on a scale from 0 to 100.

The scientists also used sensors on the face to monitor the tiny electrical signals from specific muscles. They tracked the muscle above the eyebrow used for frowning and the muscle in the cheek used for smiling. This allowed the researchers to see if participants were trying to hide their facial expressions while talking to the expert.

For their analysis, scientists specifically focused on the trials where participants initially guessed they had performed well before receiving any feedback. This allowed the researchers to observe behaviors related to self-enhancement. Self-enhancement is the natural human tendency to overestimate personal qualities to gain social approval.

The data revealed differences across the three scenarios. When participants knew they performed poorly but had to claim a top score, they reported the lowest confidence in their ability to persuade the expert. When they received positive confirmation of their top score, their confidence was at its highest.

In situations of uncertainty, participants’ confidence levels fell squarely in the middle. They felt more persuasive than when they were telling an outright lie, but less persuasive than when they were telling the absolute truth. This suggests that the lack of clear facts allowed them to partially believe their own exaggerated claims.

The physiological data mirrored these confidence ratings. The scientists found that active deception caused a significant spike in sweat gland activity, indicating heightened physiological arousal. Telling the truth was linked to a much calmer physical state with lower skin conductance.

When participants were uncertain about their actual performance, their sweat gland activity again landed between the two extremes. The body showed minor signs of stress that were higher than in the truth condition but lower than in the deception condition. The physiological evidence indicates that traces of deception still exist on an unconscious level even when a person does not know the whole truth.

“In this study, we combined behavioral and physiological measures to investigate a novel and controversial phenomenon, namely self-deception, within a socially interactive paradigm,” the researchers told PsyPost. “Our results show that both behavioral and physiological responses associated with self-deception occupy an intermediate position between those observed in truth-telling and deliberate deception, thereby offering new insights into the mechanisms underlying self-deceptive processes.”

“Moreover, the observed dissociation between explicit and implicit responses provides valuable evidence regarding the complex and still debated relationship between physiological and psychological processes in the context of truthful, deceptive, and self-deceptive tendencies.”

The facial muscle sensors did not show any significant differences across the three scenarios. Participants did not show increased frowning or smiling activity when lying compared to telling the truth. The scientists suspect this happened because the task did not trigger strong positive or negative emotional expressions that would engage those specific muscles.

The researchers propose that truth and deception do not exist as a simple binary choice. Instead, they operate on a continuous spectrum. When placed in an ambiguous situation, a person might engage in a partial lie to protect their self-image.

These findings provide evidence that uncertainty can foster a form of self-deception, allowing people to boost their own confidence while minimizing the physical stress typically associated with lying.

“There is no black and white when talking about deception,” the researchers said. “At times, to preserve their perceived image, individuals lie to themselves before lying to others.”

The study does have a few limitations to consider. The sample size was relatively small, which means the observed statistical effects were modest. Future studies should recruit larger and more diverse groups of people to see if these patterns hold true across different ages and cultures.

The current study also only looked at university students from Italy. Different cultural attitudes toward boasting and lying could potentially alter how the body responds to ambiguous situations.

“Individual differences can be a limitation here. Each one of us can have a different approach to deception,” the researchers noted. “Some may justify lying to others, while others may be stricter about it. These differences is something to keep in mind.”

Looking ahead, the scientists hope to explore the other side of these complex social interactions. “When talking about deception, we often focus on the liar,” they said. “It would be interesting to shift the focus to the person who has been lied to and perhaps see whether and how the detection of deception changes based on the level of awareness in the liar.”

The study, “The Body Knows What the Mind Does Not: Uncertainty Affects Physiological Markers of Deception,” was authored by Giulia Romano Cappi, Ilaria Mirlisenna, Alessandro Mazza, and Olga Dal Monte.