Fundamental constraints on distinguishing reality from imagination

Abstract

Humans are voracious imaginers, with internal simulations supporting memory, planning and decision-making. Because the neural mechanisms supporting imagination overlap with those supporting perception, a foundational question is how reality and imagination are kept apart. Traditional psychology experiments struggle to investigate this issue as subjects can rapidly learn that real stimuli are in play. Here we capitalised on the ability to conduct large-scale, one-trial-per-participant psychophysics via online platforms combined with computational modelling and neuroimaging to investigate perceptual reality monitoring failures in the general population. We find striking evidence for a subjective intermixing of imagination and reality – both behaviourally and neurally. Our data are best explained by a model that evaluates the total strength of intermixed imagined and perceived signals against a “reality threshold” to determine whether it reflects reality. These findings suggest that imagined and perceived signals are not kept separate, nor is the intention to imagine used to identity and discount self-generated signals. Instead, a judgment of reality is based on the intensity of the intermixture between imagination and reality. A striking consequence of this account is that it predicts when virtual or imagined signals are strong enough, they become indistinguishable from reality.

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