TABLE 1.

Overview of elements and concepts common to psychedelic experiences and examples of their implementation in Psyrreal.

Elements of psychedelic experiences	Implementation in Psyrreal
Visual acuity and color enhancement. One of the first alterations often noticed in psychedelic experiences is an enhancement of visual acuity where the visual field appears clearer and sharper and objects become more well-defined (58, 59, 69, 147). This effect is usually accompanied by an intensification and enhanced saturation of colors (58, 67, 69, 92, 148).	The experience starts in a serene, realistic environment overlooking some mountains, with birds singing and calm water flowing around the user (Figure 1 “Main”). After a brief period various open eye visual effects start to appear. Colors become brighter and more saturated; elements of drifting and morphing affect different objects as well as the whole perspective; after-images appear behind falling leaves, and flying butterflies. Certain effects on objects, such as increased contrast, edge aura, texture change and drifting, are gaze-activated (Supplementary Figure 7). Moving the gaze away from the object decreases the effect strength. As the experience progresses, the affected area can change from object edges to whole objects and to the entire scene (e.g., Figure 1 “Jewel Waterfall”).
After-images. Another visual distortion that is often noticed during the early phases of psychedelic experiences is illusory palinopsia, also called after-images, visual tracers, trails or “ghosting” where moving objects leave behind visual trails (67, 149–151).
Drifting. Objects, parts or the whole visual field often move and distort in many irregular ways, such as drifting, morphing, melting and breathing (69, 92, 147, 152). These effects can start from a slight oscillation of the outlines of specific objects to seamless drifting of textures and objects changing color or morphing from one to another (153).
Closed eye visuals (CEVs). While it is common to experience geometric patterns on real stimuli with eyes open, intricate patterns are also often reported with eyes closed. CEVs usually start out with simple geometric forms like lattices, cobwebs, honeycombs and spirals (65). Frequently, CEVs include experiences of infinite, kaleidoscopic tunnels formed of geometric patterns and texture repetition (65, 66, 69, 154).	After about 7 min of gradually increasing distortion of the environment, the experience transitions into scenes of CEVs. These start by rather dim 2D patterns which slowly become more vivid and develop into 3D spaces formed of elaborate geometric patterns akin to reports of “DMT hyperspaces” (e.g., Figure 1 “Torus”). Many of these environments also stretch infinitely in all directions (e.g., Figure 1 “Infinity”). The 2D patterns occur recurrently during the rest of the experience, increasing in complexity and acquiring rotating sculptures that generate different mandala-like visuals (Figure 1 “CEV”). One specific example of such patterned scenes are kaleidoscopic rotating tunnels (Figure 1 “Tunnel”), which tend to cause feelings of illusory self-motion and can lead to mild nausea or cyber-sickness (which might, unintuitively, benefit the therapeutic process, see Discussion).
DMT hyperspace. A special kind of visionary experience is the so-called “DMT hyperspace” where people are transported into another world (92, 154). These are often high dimensional spaces (59, 148, 154) which contain massive or even infinitely large cathedrals, machines capes or abstract spaces made of geometric patterns (154). The passage into this space, a “DMT breakthrough,” is often accompanied by sensations of overwhelming intensity, fast or accelerating movement along geometric tunnels and an ascending or intensifying sound (74, 92, 154–156).
Visions. With higher doses and during more acute phases of psychedelic experiences, CEVs can become increasingly lucid, hyperdimensional with more complex patterns, and acquire profound meaning (69, 92). Often dreamlike (70, 73) visions arise which can include whole scenes or landscapes, autobiographical memories or imagined realistic situations, as well as mythical or archetypal imagery (57, 58). Such visions are sometimes experienced in a synesthetic fashion, i.e., not just seen or imagined visually, but also “felt” (57, 58, 91).	While many levels consist of abstract shapes and patterns (e.g., Figure 1 “Organic life”), we also included levels that simulate elements of more coherent visions. “Visions” induce the feeling of being in a completely different environment from the main level. We included views of landscapes and grandiose and vast scenes (e.g., Figure 1 “Ocean”), involving large cathedrals and a mountain ridge with a floating monastery (Figure 1 “Mountains”). We also implemented the “Overview” (157–159) and “Ultraview” effects (160) where, respectively, the subject experiences an overview of the Earth (Figure 1 “Planet”) and thereafter the whole Universe.
Mystical experiences. Moderate and higher doses of psychedelics often result in participants having mystical experiences (29, 72, 77, 79). These indescribable and paradoxical experiences are often described to contain a felt union with God, Nature or the Universe, receiving transformative insights and feelings of profound peace and bliss (72, 80, 81). At the core of mystical experiences is losing a sense of individual self (see also ego-dissolution) and “becoming one” with objects of attention or with “everything” (72, 80). Another common mention is that of a bright white or golden light that could be seen or “felt” in a synesthetic nature (72, 82, 161). Mystical experiences also often contain alterations and transcendence of time and space, and feelings of vastness, awe and sacredness (58, 62, 72, 80, 92).	The synesthetic and phenomenologically barren nature of mystical experiences creates a significant hurdle in representing them in the audiovisual medium of VR. Nevertheless, we implemented a recurrently appearing level with a bright white light and calm and sacred music (Figure 1 “Mystical Light”). We also included a level with spherical particles that circle around the player, giving the impression that the environment is “alive” and interacting with the player. Psyrreal also has a soundtrack with varying tempo and intensity to induce a sense of temporal alteration (see also “Overview of Psyrreal VR”).
Ego-dissolution. Psychedelic experiences also bring about alterations of the sense of self which are often discussed under the term ego-dissolution (or “ego-death”) (57, 162–166). This is often reported as a dissolution of the embodied self, disintegration of self-related thoughts and felt ownership of thoughts (60, 164, 167), and/or cessation of implicit subject-object distinction as the subject feels as “one” with their surroundings (57, 72).	To emulate ego-dissolution, we included a virtual body representation of the user in certain levels which consists of a sphere that mimics the environment, thus creating a sense of connectedness to the virtual “world.” At the culmination of the experience the particles of the universe converge at the position of the subject to then explode outward and fade, disintegrating the virtual self.