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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

Understanding the Boundary Between Reality and Imagination

Overview/Introduction

Humans possess a remarkable ability to imagine, which aids in memory, planning, and decision-making. However, the brain's mechanisms for distinguishing between real and imagined experiences are complex, as the neural processes for both overlap. This study explores how we differentiate reality from imagination, proposing that the strength of sensory signals plays a crucial role. When imagined signals are strong enough, they may become indistinguishable from reality.

Methodology

To investigate this, researchers used a combination of psychophysics, computational modeling, and neuroimaging. They designed experiments where participants imagined visual stimuli while viewing dynamic noise. On a critical trial, a real stimulus was subtly introduced, and participants were asked to judge whether what they saw was real or imagined. This approach ensured participants remained unaware of the real stimuli, allowing for genuine assessments of reality perception.

Key Findings

  • Intermixed Signals: The study found that imagined and perceived signals are intermixed. Reality judgments depend on whether the combined signal strength crosses a certain threshold.
  • Reality Threshold: If imagined signals are vivid enough, they can be perceived as real. This suggests that our brain uses sensory strength to determine reality.
  • Neural Correlates: Neuroimaging revealed that the same brain areas track both the vividness of imagined images and the visibility of real stimuli, supporting the idea of shared neural pathways.

Implications

  • Perceptual Reality Monitoring: The findings suggest that reality monitoring is not about separating imagination from perception but about evaluating the strength of sensory experiences.
  • Clinical Relevance: This model could explain hallucinations, where strong internal signals are mistaken for reality. It highlights the importance of maintaining a well-calibrated reality threshold, especially with advancing technologies like virtual reality.

Limitations

  • Task Engagement: The online nature of the experiments might have affected participant engagement, although simulations showed that qualitative differences between conditions remained consistent.
  • Individual Differences: Variations in imagery vividness and perceptual sensitivity among participants could influence results, suggesting a need for further research to explore these individual factors.
This study provides a new perspective on how we perceive reality, emphasizing the role of sensory strength in distinguishing real from imagined experiences. As technology evolves, understanding these mechanisms becomes increasingly important to ensure our perceptions remain accurate.