Shared and Diverging Neural Dynamics Underlying False and Veridical Perception.

We often mistake visual noise for meaningful images, which sometimes appear as convincing as veridical percepts. This suggests considerable overlap between the mechanisms that underlie false and veridical perception. Yet, false percepts must arise at least in part from internally generated signals. Here, we apply multivariate analyses to human MEG data to study the overlap between veridical and false perception across two aspects of perceptual inference: discrimination of content (what did I see?) and detection (did I see something?). Male and female participants performed a visual discrimination task requiring them to indicate the orientation of a noisy grating, as well as their confidence in having seen a grating. Importantly, on 50% of trials, only a noise patch was presented. To exclude external signals driving false percepts, noise patches were carefully designed not to contain orientation signal. Still, participants occasionally confidently reported seeing a grating on noise only trials, i.e., false percepts. Decoding analyses revealed a sensory signal reflecting the content of these false percepts, despite no such grating being physically presented. Uniquely, high confidence false, but not veridical, percepts were associated with increased prestimulus high alpha/low beta [11-14 Hz] power, potentially reflecting enhanced reliance on top-down signaling on false percept trials. Later on, a shared neural code reflecting confidence in stimulus presence emerged for both false and veridical percepts. These findings suggest that false percepts arise through neural signals reflecting both sensory content and detection, similar to veridical percepts, with an increase in prestimulus alpha/beta power uniquely contributing to false percepts.