UnReal? Investigating the Sense of Reality and Psychotic Symptoms with Virtual Reality

Abstract

Distortions of reality, such as hallucinations, are common symptoms of many psychiatric conditions. Accordingly, sense of reality (SoR), the ability to discriminate between true and false perceptions, is a central criterion in the assessment of neurological and psychiatric health. Despite the critical role of the SoR in daily life, little is known about how this is formed in the mind. Here, we propose a novel theoretical and methodological framework to study the SoR and its relation to psychotic symptoms. In two experiments, we employed a specialized immersive virtual reality (VR) environment allowing for well-controlled manipulations of visual reality. We first tested the impact of manipulating visual reality on objective perceptual thresholds (just noticeable differences). In a second experiment, we tested how these manipulations affected subjective judgments of reality. The results revealed that the objective perceptual thresholds were robust and replicable, demonstrating that SoR is a stable psychometric property that can be measured experimentally. Furthermore, reality alterations reduced subjective reality judgments across all manipulated visual aspects. Finally, reduced sensitivity to changes in visual reality was related to self-reported prodromal psychotic symptoms. These results provide evidence for the relevance of SoR in the assessment of psychosis and other mental disorders in which reality is distorted.

Keywords: derealization; hallucinations; psychosis; sense of reality; virtual reality.

Figure 1

Experimental setup and design. (A) Center, illustrative image of the experimental setup and visual scenario. Participants donned a head-mounted display (HMD) and viewed the immersive virtual environment in 360° around them. The images on the sides and bottom represent the six types of alterations of the visual aspects employed, at the highest magnitude of alteration shown, for comparison, on a similar section of the virtual room. (B) Trial flow for the experiments. (Top) In Experiment 1, a virtual reality (VR) environment appeared for 2 s, followed by a black screen and then a second VR environment. Subsequently, participants were presented a question screen asking them to report if the two VR environments were identical or not. (Bottom). In Experiment 2, participants viewed a VR environment, which could be altered or unaltered. In each trial, they were required to judge on a continuous scale how ‘real’ the environment felt to them.

Figure 2

Perceptual thresholds for reality alterations. (A,B). Convergence rates of the staircase procedure in aspects grow and grain, respectively. Y-axis shows the magnitude of the reality alteration and the x-axis denotes the number of iterations. Note individual participants (colored lines) converged towards a stable perceptual threshold. (C) A comparison between JNDs of grow and shrink aspects that shared a common scale. (D) Pearson correlation matrix between JNDs across all aspects. Note high, positive, and significant correlations were found between all aspects’ JNDs, with the exception of grain. (E) Example of correlation between participants’ grow and shrink JNDs. (F). Averaged correlations of The Cardiff Anomalous Perceptions Scale (CAPS) and the Prodromal Questionnaire Brief Version (PQ-B) scores with JNDs shown by aspect domains (i.e., self, nature, perception).

Figure 3

Subjective judgments of reality. (A–F) Changes in subjective reality affected the ratings of Sense of Reality (SoR) in a relatively consistent manner. Reality ratings for unaltered environments were highest while ratings for altered environments were reduced, suggesting a consistent tuning curve for SoR. (G) Subjective ratings for all aspects showed high, positive, and significant correlations. (H) Example of the correlation between participants’ subjective rating of grow and shrink. (I) Significant difference between the drop in subjective ratings for grow and shrink, indicating an asymmetrical response for inducing changes in the first person perspective (1PP).