[The results of a new neuroimaging study support the idea that the more vividly we imagine a stimulus or perceive one that is “virtual” (mediated by technology), the more likely our brain will struggle to determine whether it is real. The news release from University College London below summarizes the study and is followed by two key paragraphs from the published journal article. –Matthew]
[Image: A graphical representation of the supported hypothesis. Part of Figure 1b in the article “Subjective signal strength distinguishes reality from imagination”]
Humans struggle to differentiate imagination from reality
April 21, 2023
The more vividly a person imagines something, the more likely it is that they believe it’s real, finds a new study by UCL researchers.
The research, published in Nature Communications, involved over 600 participants who took part in an online experiment, where they were asked to imagine images of alternating black and white lines while looking at a computer screen.
After they imagined a stimulus, participants then had to report how vividly they were able to visualise it.
Then, without the participant’s knowledge, at the very end of the experiment, an actual stimulus with the same features as those the participant was imagining was gradually faded in to view on the computer screen. Participants then had to rate how vividly they imagined the stimulus and described whether what they saw was real or imagined.
The results showed that the imagined and perceived stimuli became intermixed in the participants’ minds. For example, when a real stimulus was faded in, participants believed that their imagination had simply become more vivid.
Meanwhile, when imagining more vividly, the participants were more likely to believe that they had seen a real stimulus – even when nothing had been presented to them.
Lead author, Dr Nadine Dijkstra (Wellcome Centre for Human Neuroimaging at UCL) said: “In daily life, we often imagine things that are not there. For example, if we are asked whether a cat’s ears are round or pointy, we might inspect a mental image in our mind’s eye to answer the question.
“Neuroscience has discovered that imagination and perception rely on overlapping brain circuits. We were interested in whether this overlap leads to confusion between the two: given that the same circuits are involved – how can we be sure what is real and what is not?”
The researchers used a computer model to establish whether the pattern of results was consistent with the theory that people judge whether something is real or imagined, based on how vividly they experience it.
The team validated this model using neuroimaging, showing that the brain encodes the strength or vividness of real and imagined stimuli in a similar manner – confusing reality and imagination.
Dr Dijkstra, said: “Our results suggest that, counterintuitively, there is no categorical difference between imagination and reality; instead, it is a difference in degree, not in kind.”
Senior author, Professor Stephen Fleming (UCL Psychology & Language Sciences, Wellcome Centre for Human Neuroimaging at UCL, and Max Planck UCL Centre for Computational Psychiatry & Ageing Research) added: “Normally imagination is relatively weak, and so we don’t confuse it with reality. But if imagination becomes strong or vivid enough, it may get treated as real.
“In near-future scenarios, in which brain stimulation or virtual reality technology become novel sources of strong sensory signals, our findings imply it may be more difficult than we think to tell apart reality and unreality.”
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Key excerpts from Dijkstra, N., Fleming, S.M. (2023). Subjective signal strength distinguishes reality from imagination. Nature Communications, 14, 1627. https://doi.org/10.1038/s41467-023-37322-1:
“In a behavioural study, participants were instructed to vividly imagine a stimulus while looking at dynamic noise and then report the vividness of their imagery. Then, unbeknownst to the participant, on a final, critical trial, a stimulus that was either congruent or incongruent with participants’ imagery gradually appeared in the noise until it was around detection threshold. After again reporting their imagery vividness on this critical trial, participants were asked whether they thought a real stimulus had been presented on the last trial, or whether what they had experienced was only imagined. Participants’ answers to this last question provided a direct, unbiased test of perceptual reality monitoring, in the absence of expectations or prior instructions that external stimuli might be presented.”
“Taken together, our results reveal a subjective intermixing of imagery and perception, leading to widespread perceptual reality monitoring failure in large general population samples. The success of a signal detection model in capturing these data patterns indicates that reality monitoring may be implemented simply by comparing sensory signals against a reality threshold. Such a model is parsimonious and powerful, but also has profound implications. In particular, a consequence of this account is that it predicts when virtual or imagined sensory signals are strong or detailed enough, they become indistinguishable from reality. While currently the most common driver of top-down signals is imagination, in near-future scenarios in which brain stimulation and/or virtual reality technology is used to drive sensory signals we might be less able to tell apart reality from unreality than we would like to believe. Our model provides a framework within which to investigate these issues, and offers a route towards ensuring our reality thresholds remain well-calibrated in the face of technological advances.”