Everyday mental quirks like déjà vu might be natural byproducts of a resting mind

A recent study published in Consciousness and Cognition provides evidence that everyday mental quirks like déjà vu or tip of the tongue states are natural byproducts of a resting mind. The findings suggest that when a person’s attention is not fully occupied, a wide variety of spontaneous thoughts and reflective feelings naturally emerge into awareness.

The scientists conducted the research to understand if a broad spectrum of unprompted mental experiences could be systematically captured in a laboratory setting. Past research has mostly focused on involuntary memories, which are recollections of personal events that pop into the mind without warning. The team wanted to know if the same boring, repetitive conditions that produce these memories might also generate other spontaneous phenomena.

They specifically focused on metacognition. Metacognition is a term used to describe the brain’s ability to think about and monitor its own processes. While people sometimes use metacognition deliberately, such as trying to gauge how well they learned a topic for a test, it can also happen without effort.

Spontaneous metacognition includes sudden feelings like déjà vu, which is the sensation that a new situation is highly familiar. It also includes the sudden realization that a well known word looks strangely incorrect, a phenomenon known as jamais vu.

“This study was motivated by the observation that many mental experiences—such as déjà vu, tip-of-the-tongue states, or sudden memories—seem to appear spontaneously in everyday life, yet they are usually studied separately in different areas of psychology,” explained study author Krystian Barzykowski, the head of the Applied Memory Research Laboratory at Jagiellonian University and Marie Skłodowska-Curie Postdoctoral Fellow at the Grenoble Alpes University.

“We wanted to take a broader look at human cognition and move beyond examining only a small slice of our everyday mental life at a time. By using a laboratory paradigm known to elicit involuntary autobiographical memories, we tested whether it could also capture a wider range of spontaneous experiences. The goal was to see whether these common mental events might emerge together and help us understand how different aspects of spontaneous cognition are related.”

For their study, the researchers recruited 96 university students to complete a low demand vigilance task. This type of task is deliberately boring and requires very little mental effort, which creates an ideal environment for the mind to drift. Participants looked at a series of 400 slides on a computer screen for about an hour.

Each slide showed a background image or a word overlaid with a pattern of horizontal or vertical lines. The participants had a simple job that required constant but shallow attention. They were instructed to press a specific key on their keyboard only when they saw the rare vertical lines.

The background images included familiar pictures of the local city in France, unfamiliar pictures of foreign cities in Pakistan, real French words, and made-up words. Participants were told to ignore these background items and focus entirely on the line patterns. However, they were also asked to press the spacebar anytime they experienced a spontaneous thought or mental state during the task.

When they pressed the spacebar, the experiment paused so they could categorize their experience. The options included involuntary memories, déjà vu, jamais vu, zoning out, detecting a mistake they just made, and tip of the tongue states. A tip of the tongue state is the frustrating feeling that you know a piece of information but cannot quite bring it to mind.

The researchers found that participants experienced a wide variety of these mental states. Unprompted memories of the past were the most frequently reported experience. These memories were most often triggered by familiar pictures and real words. Déjà vu was the second most common experience. It tended to happen most often when participants viewed both familiar and unfamiliar pictures.

The scientists observed a positive association between the two most frequent experiences. Participants who had more involuntary memories also tended to report more instances of déjà vu.

This connection provides evidence that these two phenomena share a common mental mechanism. A cue in the environment might trigger the brain’s memory retrieval system. Instead of bringing forth a specific memory, the process sometimes stalls and only delivers a vague feeling of familiarity.

Other mental states occurred less frequently but were still consistently present. For example, participants reported feeling jamais vu most often when looking at the made-up words. Zoning out happened at a steady rate throughout the experiment regardless of what was on the screen.

Tip of the tongue states and sudden error detections were the rarest events. This is likely because the ongoing task did not demand complex problem solving or active memory retrieval.

“One interesting observation was how reliably the task elicited not only involuntary memories but also several other spontaneous experiences,” Barzykowski told PsyPost. “While we expected involuntary autobiographical memories to appear, it was notable that phenomena such as déjà vu and tip-of-the-tongue states also emerged within the same experimental context.”

The scientists also asked participants to rate their experiences based on how spontaneous they felt, how strong the feeling was, and how much it distracted them from the main task. Across all types of mental states, the ratings for spontaneity and intensity were surprisingly similar. This supports the idea that these sudden thoughts are rapid, uninvited events that briefly pull a person’s attention away from the outside world and toward their internal mind.

The researchers also noted a relationship between how well participants performed the line-matching task and how many mental states they reported. People who were highly accurate at detecting the rare vertical lines tended to report fewer spontaneous thoughts overall. They also reported fewer instances of déjà vu, suggesting that deep focus on an external task leaves less mental space for these internal feelings to arise.

“One takeaway is that many unusual mental experiences—such as suddenly remembering something from the past, feeling déjà vu, or having a tip-of-the-tongue moment—are not rare or mysterious glitches of the mind,” Barzykowski explained. “Instead, they appear to be natural byproducts of how our cognitive system continuously processes information in the background.”

“Our findings suggest that when the mind is not fully occupied by demanding tasks, a variety of spontaneous thoughts and feelings can emerge into awareness. In other words, these experiences may reflect normal and adaptive aspects of how the mind monitors information and connects the present moment with stored knowledge and memories.”

Like all research, the study does have some limitations. Because the experiment relied on participants to notice and report their own thoughts, some people may have missed fleeting mental states. Providing definitions for these experiences beforehand might have also shaped what participants expected to feel during the task.

Additionally, some of the laboratory induced experiences lacked the emotional intensity that people typically feel when these events happen naturally. For instance, the déjà vu felt in the lab was often rated as less intense than the surprising and sometimes unsettling déjà vu felt in the real world. This suggests that the sterile laboratory environment might not fully capture the richness of these mental states.

“One long-term goal of this research is to better understand spontaneous cognition—that is, the thoughts, memories, and feelings that arise in the mind without deliberate effort,” Barzykowski said. “In the future, we would like to refine laboratory methods that allow us to capture a wider range of these experiences and examine how they relate to each other.

“We are also interested in understanding why people differ in how frequently they experience phenomena such as involuntary memories, déjà vu, or tip-of-the-tongue states, and whether these differences may influence everyday cognitive functioning. Ultimately, this line of work may help us better understand how the mind continuously monitors information and connects past experiences with the present moment.”

“I would also like to highlight that this study was the result of collaborative research supported by several funding initiatives. Gull Zareen was partly supported by the French National Research Agency. My own work was supported by the European Union’s Horizon research and innovation programme through a Marie Skłodowska-Curie Postdoctoral Fellowship. The views expressed in the study are those of the authors and do not necessarily reflect those of the European Union or the European Commission.”

The study, “Spontaneous metacognitive experiences and involuntary memories in the laboratory,” was authored by Gull Zareen, Céline Souchay, Krystian Barzykowski, and Chris J.A. Moulin.