Summary: A new study finds that the brain represents the vividness of imagined and perceived experiences in similar ways, which can cause people to confuse imagination with reality when their mental images become strong.
Source: UCL
Researchers at University College London report that the more vividly someone imagines something, the more likely they are to judge it as real.
Published in Nature Communications, the study tested over 600 participants in an online experiment. Participants repeatedly imagined a visual pattern—alternating black and white lines—while viewing a blank computer screen. After each trial they rated how vividly they could see the imagined pattern.
At the very end of the session, without warning, a real stimulus with the same visual characteristics was gradually faded into view on the screen for a subset of trials. Participants again rated the vividness of their mental image and indicated whether what they experienced was real or imagined.
Results showed that imagined and perceived images became mixed in participants’ minds. When a real stimulus was slowly revealed, participants often reported that their imagination had simply grown more vivid rather than recognizing a new sensory input. Conversely, when participants produced especially vivid mental images, they were more likely to report having seen an actual stimulus even when none was presented.
Lead author Dr. Nadine Dijkstra (Wellcome Centre for Human Neuroimaging at UCL) explains that everyday tasks often rely on inspecting mental images—such as deciding whether a cat’s ears are pointy or round. Neuroscience has long shown that imagination and perception use overlapping brain circuits. The team’s question was whether that overlap leaves room for confusion between what is imagined and what is genuinely perceived.
To test the idea that perception and imagination are distinguished by subjective signal strength, the researchers built a computational model. The model predicts that the brain judges reality by whether the combined internal and external signal crosses a threshold for “realness.” In other words, if the internally generated signal from imagery is strong enough, it can be mistaken for a real sensory event.
The team validated the model using neuroimaging. Brain activity patterns indicated that the neural code for the strength or vividness of a stimulus looked similar whether the stimulus was externally presented or internally generated. In other words, vividness itself appears to be encoded in a comparable way across perception and imagery, which can blur the boundary between reality and imagination.
Dr. Dijkstra summarizes the implication: “Our results suggest that, counterintuitively, imagination and reality are not categorically different; they differ in degree rather than kind.”
Senior author Professor Stephen Fleming (UCL Psychology & Language Sciences, Wellcome Centre for Human Neuroimaging, and Max Planck UCL Center for Computational Psychiatry & Aging Research) adds that in normal circumstances mental images are relatively weak, so they rarely get mistaken for real perception. However, when imagination becomes intense or when future technologies produce strong internal-like signals—for example through advanced brain stimulation or immersive virtual reality—people may find it harder to distinguish real sensory input from internally generated experience.
About this perception research news
Author: Press Office (UCL)
Source: UCL
Contact: Press Office – UCL
Image: The image is in the public domain
Original Research: Open access.
“Subjective signal strength distinguishes reality from imagination” by Nadine Dijkstra et al., Nature Communications
Abstract
Subjective signal strength distinguishes reality from imagination
Humans frequently rely on internal simulations to support memory, planning and decision-making. Because the neural mechanisms that support imagery overlap with those that support perception, an important question is how the brain distinguishes reality from imagination.
One possibility is that the intention to imagine allows the mind to tag and discount self-generated signals. An alternative is that internally generated signals are typically weaker than sensory input, so sensory strength is used to infer reality. Traditional experiments face challenges because participants can quickly learn when real stimuli are present.
This study combined one-trial-per-participant psychophysics with computational modeling and neuroimaging to show that imagined and perceived signals intermingle. Judgments of reality depended on whether the overall signal surpassed a threshold for reality. A direct consequence of this framework is that when imagined or virtual signals become sufficiently strong, they can be subjectively indistinguishable from real perception.