Involuntary memories and related mental phenomena such as déjà vu emerge most often during routine, low-focus activities and appear to be a constant layer of background activity in the human mind, according to a study led by researchers at the Jagiellonian University.
The research suggests that memory processes remain continuously active, even when attention is directed elsewhere, and are frequently triggered by familiar environmental cues such as sights, sounds or smells.
The human mind never ‘switches off’. Even when we perform simple tasks like cleaning, our cognitive processes, especially memory, remain active.
“You could say that memory is always on and constantly monitors both the environment and our internal states. In such conditions, when attention is not fully engaged in a specific task, spontaneous thoughts and feelings emerge more easily”, said Krystian Barzykowski from the university’s Institute of Psychology.
The findings, published in Consciousness and Cognition (doi.org/10.1016/j.concog.2025.103976), are based on a study conducted by a French-Polish research team led by Barzykowski and Chris Moulin of the Université Grenoble Alpes.
Researchers tested 96 participants who performed a sustained attention task involving long periods of monotonous stimuli, during which they had to respond only to rare signals while ignoring background words, images and letter strings.
Participants were asked to report any spontaneous mental experiences as they occurred, then classify them into categories such as involuntary autobiographical memories, déjà vu, jamais vu, “tip-of-the-tongue” states, zoning out and error detection.
The most common experience reported was involuntary autobiographical memory — fragments of personal past experiences that appeared without conscious effort and were often triggered by familiar stimuli.
“Déjà vu came in second, less frequent but still regular. Jamais vu, zoning out, and error detection ranked next. ‘Tip-of-the-tongue’ states were the rarest”, Barzykowski said.
Researchers suggest that involuntary memories and déjà vu may arise from the same underlying memory activation process, differing only in intensity.
The study found that stronger activation of memory traces produces a specific recollection, while weaker activation results in a feeling of familiarity without clear recall, experienced as déjà vu.
“The difference lies in the strength of this activation. If it is strong enough, a specific memory emerges. If not, we only experience a sense of familiarity with the situation, i.e., déjà vu”, Barzykowski explained.
The research also identified patterns suggesting that people prone to one type of spontaneous experience are often more prone to others, indicating a broader cognitive tendency toward spontaneous mental activity.
The type of stimulus also influenced which experiences emerged. Familiar visual scenes, especially photographs of known locations, were more likely to trigger involuntary memories and déjà vu.
By contrast, meaningless or unfamiliar words were more likely to produce jamais vu and error-detection experiences, in which familiar things suddenly feel strange or incorrect.
Researchers said the laboratory findings matched participants’ reports of everyday experiences, suggesting these phenomena are stable features of cognition rather than experimental artefacts.
The study is part of the EU-funded Marie Skłodowska-Curie project “SpontaneousPAST: Using déjà vu to better understand spontaneous retrieval in human memory”, led by Barzykowski. Further project results are available here.
Ewelina Krajczyńska-Wujec (PAP)
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