# The Body Knows What the Mind Does Not: Uncertainty Affects Physiological Markers of Deception

## TL;DR

This study shows that uncertainty leads to physiological responses between truth and deception, suggesting a partial form of lying.

## Contribution

First study to examine both explicit and implicit responses to uncertainty in deception contexts.

## Key findings

- Participants showed lower self-confidence during deception compared to truth-telling.
- Uncertainty led to physiological responses between deception and truth.
- Uncertainty may enable partial deception, reducing the costs of lying.

## Abstract

Humans, as social beings, may choose to be either truthful or deceptive to achieve personal benefits. Although deception and truth‐telling are distinct, both rely on an individual's certainty about the world, shaping responses associated with honesty or lying. However, our surrounding environment is often characterized by a lack of certainty, and little is known about the psychophysiological responses in situations of uncertainty, where individuals lack confidence in whether their statements are truthful or deceptive. In this study, we implemented a within‐subject design where thirty‐two participants (mean age: 23.94; age range: 19–32; 17 females) were asked to persuade another person about the goodness of their performance in cognitively demanding tasks, while their self‐confidence, electrodermal activity (EDA), and facial muscle activity were measured under three conditions: Deception, Uncertainty, and Truth. Participants reported lower self‐confidence in convincing an interlocutor of their great results during Deception compared to Truth. Deceptive behavior was also associated with increased physiological arousal (trough‐to‐peak; TTP) compared to truth‐telling. Crucially, when faced with uncertainty, participants exhibited behavioral and physiological responses that fell in between those of Deception and Truth, self‐enhancing their performance while retaining residual characteristics of deception at the implicit level. We propose that these results could be framed within a continuum between truth and deception, where uncertainty can give rise to a form of partial deception, allowing individuals to enhance their self‐confidence while reducing the social and physiological drawbacks of lying.

Deception and truth‐telling rely on an individual being certain about the state of the world. While much research has been done on deceptive and truth‐telling behaviors, less is known about psychophysiological correlates of uncertainty, that is, when individuals cannot confidently know if they are lying or telling the truth, due to a lack of information. In this study, we examined for the first time both the explicit (self‐confidence) and implicit (electrodermal and facial muscle activity) responses to uncertainty. Our findings suggest that responses to uncertain stimuli tend to fall between those typically associated with deception and truth. These results support the idea of a continuum between truth and deception, where uncertainty can lead to a partial lie or self‐deception, enabling individuals to enhance their self‐confidence while minimizing the social and physiological costs of lying.