Unreal? A Behavioral, Physiological, and Computational Model of the Sense of Reality

An intriguing aspect of the human mind is our knowledge that our perceptions may be false. Our frequent exposure to non-veridical perceptions such as those found in dreams, illusions and hallucinations cause us to examine the actuality of our sensory experiences. As such humans continuously monitor the veridicality of their perceptions in a process termed the Sense of Reality (SoR). Moreover, the Sense of Reality is a central criterion in the assessment of neurological and psychiatric health. The scientific study of hallucinatory experiences has been hindered by their transitory, subjective, ineffable nature and by the fact that they typically co-occur with psychiatric, medical or psychedelic states. Despite the critical role of SoR in daily life and in pathologies little is known regarding its cognitive, physiological and computational underpinnings. Here we employed a novel immersive virtual reality paradigm to induce Virtual Hallucinations (VH) simulating the phenomenology of visual hallucinations found in psychiatric, neurological, and pharmacological conditions. Combining psychophysics, physiological recordings and computational modeling in one exploratory (n = 31) and one preregistered experiment (n = 32) we examined responses to VH of varying magnitudes and domains. Judgments of SoR varied depending on the magnitude and domain of VH. These were accompanied by distinct motor, pupillometric and cardiac responses. Finally, sense of reality can be well explained by a computational model in which decisions of reality are based on comparison of current sensory experience to an internal model of the world. Our results shed some light on the age-old question ‘how do we know what is real’?