Is this the real life? Is this just fantasy? Neural correlates of perceptual reality monitoring

When walking down the street, we are bombarded with visual input. Different colours, shapes and textures are processed by our visual system to create the technicolour perception we experience every day. At the same time, while we are thinking about things that we will do later or things that we have already done, we experience a rapid stream of mental images. Mental imagery relies on similar neural mechanisms as visual perception. Imagining and perceiving the same stimulus is associated with similar patterns of neural activation throughout the visual system and similar connectivity between different brain areas. However, we do not generally confuse what is real with what is imagined. In this project, I aimed to investigate the neural mechanisms underlying this ability for “reality monitoring”. Given the large neural overlap between imagery and perception, how does the brain know whether what we see is real or imagined? Understanding how the brain keeps track of what is real and what is imagined will provide new perspectives on our understanding of disorders of reality monitoring. For example, in psychosis, the line between imagination and reality blurs, and patients might start believing that what they imagine is real. The objectives of the project were as follows: First, I planned to determine if the decision process that determines whether a current visual experience has an external or internal source is supported by the medial prefrontal cortex. Next, I planned to investigate whether the middle layer of the visual cortex could provide evidence for this source attribution. Finally, I aimed to investigate how source-relevant evidence was integrated in the brain over time.

We first wrote a review on the current state-of-the-art in perceptual reality monitoring research. Next, we developed an experimental set-up that allowed us to investigate confusion between imagination and reality under controlled settings in healthy volunteers. In this set-up, participants had to imagine specific pictures while also looking for them in white noise. We found that participants were able to mistake vivid imagination for reality in this paradigm. After that, we developed computational models that could help us figure out which factors determined whether imagery and perception would be confused. We found evidence in favour of a model in which imagined and perceived signals are completely intermixed in the brain, and whether or not something is experienced as real determines on whether it is vivid enough to cross a 'reality threshold'. Next, we scanned people's brains with functional magnetic resonance imaging (fMRI) while they were doing the same task and again found evidence if favour of our reality threshold model.

Exploitation and dissemination of the results:
Journal articles:
- Dijkstra, N., Kok, P., & Fleming, S. (2022). Perceptual reality monitoring: neural mechanisms dissociating imagination from reality. Neuroscience & Biobehavioural Reviews, 104557.
- Dijkstra, N., Kok, P., & Fleming, S. (2022). Imagery adds stimulus-specific sensory evidence to perceptual detection. Journal of Vision, 22 (2), 11
- Mazor, M.*, Dijkstra, N.*, Fleming, S. (2022). Dissociating the neural correlates of subjective visibility from those of decision confidence. Journal of Neuroscience, 42 (12), 2562-2569.
- Dijkstra, N., & Fleming, S. (2023). Subjective signal strength distinguishes imagination and reality. Nature Communications, 14, 1627.
- Barnett, B., Andersen, L.M. Fleming, S.*, & Dijkstra, N.* (in press) Identifying content-invariant neural signatures of phenomenal magnitude. PNASnexus

Invited talks:
2023 Sussex Neuroscience Seminar, Sussex, UK
2023 Department of Experimental Psychology, University of Utrecht, the Netherlands
2023 Perception in Action Research Centre, Magquarie University, Australia
2023 Action and Perception Lab, Birkbeck, London, UK
2023 Visual Cognitive Neuroscience lab, Donders Institute, the Netherlands
2023 Neurotech lab, Donders Insitute, the Netherlands
2022 City University of New York Colloquium, US
2022 Nence lab, Antwerp, Belgium
2022 Northern Imagination Forum, Glasgow, Scotland
2022 Experimental Psychology Society, UK

The development of our novel experimental paradigm will allow us to investigate perceptual reality monitoring in a wide range of circumstances in healthy volunteers. This will give us the possibility to answer questions such as: which characteristics determine whether somebody is more likely to confuse imagination and reality? Are these related to the likelihood of developing reality monitoring disorders? Under which circumstances are reality and imagination more confusable? Could this help us improve virtual reality techniques? Furthermore, the novel idea of a 'reality threshold' that distinguishes reality from imagination suggests a potential mechanism for hallucinations. We are currently planning studies that link our findings to hallucination-proneness in the general population. Eventually, these discoveries will provide new perspectives on treatments for disorders of reality monitoring.

Periodic Reporting for period 1 - RealOrImagined (Is this the real life? Is this just fantasy? Neural correlates of perceptual reality monitoring)

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