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Subjective signal strength distinguishes reality from imagination

DOI: 10.1038/s41467-023-37322-1
Dijkstra, N., & Fleming, S. M. (2023). Subjective signal strength distinguishes reality from imagination. Nature Communications, 14(1). doi:10.1038/s41467-023-37322-1

Abstract

Humans are voracious imaginers, with internal simulations supporting memory, planning and decision-making. Because the neural mechanisms supporting imagery overlap with those supporting perception, a foundational question is how reality and imagination are kept apart. One possibility is that the intention to imagine is used to identify and discount self-generated signals during imagery. Alternatively, because internally generated signals are generally weaker, sensory strength is used to index reality. Traditional psychology experiments struggle to investigate this issue as subjects can rapidly learn that real stimuli are in play. Here, we combined one-trial-per-participant psychophysics with computational modelling and neuroimaging to show that imagined and perceived signals are in fact intermixed, with judgments of reality being determined by whether this intermixed signal is strong enough to cross a reality threshold. A consequence of this account is that when virtual or imagined signals are strong enough, they become subjectively indistinguishable from reality.

Authors

  • Nadine Dijkstra2
  • Stephen M. Fleming1

What This Study Is About

Researchers wanted to know how our brains tell the difference between the real world and our imagination. They tested a theory that the brain doesn’t have a "real" or "imagined" label for what we see; instead, it simply measures how strong a visual signal is to decide if it’s actually there.

How They Studied It

The researchers conducted large online experiments with over 600 participants. People were asked to imagine a faint pattern (like tilted lines) while looking at a screen of "static" (like a TV with no signal).
Sometimes, the researchers secretly showed a real, faint pattern on the screen; other times, they showed nothing at all. Participants had to rate how vivid their mental imagery was—their ability to "see" the object in their mind—and then decide if what they saw was real or just imagined. They also re-analyzed brain scans (fMRI) to see which parts of the brain track these signals.

What They Found

The study found that imagination and reality are "intermixed" in the brain. It works like a volume knob:
  • If your imagination is "loud" (vivid) enough, it crosses a "reality threshold," and your brain thinks it’s a real object.
  • If a real object is "quiet" (faint) enough, your brain might dismiss it as just your imagination.
People with very vivid mental imagery were much more likely to mistake their imagination for reality. The brain scans showed that the same "strength meter" in the front of the brain is used to judge both real sight and imagination.

What This Might Mean

This suggests that aphantasia—the inability to create mental images—might actually make someone a "pro" at reality monitoring. If you have aphantasia, your "internal volume" for imagery is essentially at zero, meaning you are much less likely to mistake a thought for a real-world object.
While this study is a huge step in understanding how we perceive the world, it was mostly done through online tests. We need more studies specifically comparing people with aphantasia to those with "hyper-vivid" imagery to see if this "volume knob" theory holds up for everyone.

One Interesting Detail

The researchers found that if you are already imagining something and a real version of that object appears, your brain combines them into one "super-signal," making the object feel even more real and vivid than it actually is!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.