Fabian Unruh, M.Sc.

Abstract: This paper presents a novel approach to altering how time is perceived in Virtual Reality (VR). It involves manipulating the speed and pattern of motion in objects associated with timekeeping, both directly (such as clocks) and indirectly (like pendulums). Objects influencing our perception of time are called ‘zeitgebers‘; for instance, observing a clock or pendulum tends to affect how we perceive the passage of time. The speed of motion of their internal parts (clock hands or pendulum rings) is explicitly or implicitly related to the perception of time. However, the perceptual effects of accelerating or decelerating the speed of a virtual clock or pendulum in VR is still an open question. We hypothesize that the acceleration of their internal motion will accelerate the passage of time and that the irregularity of the orbit pendulum’s motion will amplify this effect. We anticipate that the irregular movements of the pendulum will lower boredom and heighten attention, thereby making time seem to pass more quickly. Therefore, we conducted an experiment with 32 participants, exposing them to two types of virtual zeitgebers exhibiting both regular and irregular motions. These were a virtual clock and an orbit pendulum, each operating at slow, normal, and fast speeds. Our results revealed that time passed by faster when participants observed virtual zeitgebers in the fast speed condition than in the slow speed condition. The orbit pendulum significantly accelerated the perceived passage of time compared to the clock. We believe that the irregular motion requires a higher degree of attention, which is confirmed by the significantly longer gaze fixations of the participants. These findings are crucial for time perception manipulation in VR, offering potential for innovative treatments for conditions like depression and improving wellbeing. Yet, further clinical research is needed to confirm these applications.

Abstract: This paper presents a novel experiment investigating the relationship between virtual disembodiment and time perception in Virtual Reality (VR). Recent work demonstrated that the absence of a virtual body in a VR application changes the perception of time. However, the effects of simulating an out-of-body experience (OBE) in VR on time perception are still unclear. We designed an experiment with two types of virtual disembodiment techniques based on viewpoint gradual transition: a virtual body’s behind view and facing view transitions. We investigated their effects on forty-four participants in an interactive scenario where a lamp was repeatedly activated and time intervals were estimated. Our results show that, while both techniques elicited a significant virtual disembodiment perception, time duration estimations in the minute range were only shorter in the facing view compared to the eye view condition. We believe that reducing agency in the facing view is a key factor in the time perception alteration. This provides first steps towards a novel approach to manipulating time perception in VR, with potential applications for mental health treatments such as schizophrenia or depression and for improving our understanding of the relation between body, virtual body, and time.

Abstract: This article explores the effect of one’s body representation on time perception. Time Perception is modulated by a variety of factors including, e.g., the current situation or activity, it can display significant disturbances caused by psychological disorders, and it is influenced by emotional and interoceptive states, i.e., ”the sense of the physiological condition of the body”. We investigated this relation between one’s own body and the perception of time in a novel Virtual Reality (VR) experiment explicitly fostering user activity. 36 participants randomly experienced different degrees of embodiment: i) without an avatar (low), ii) with hands (medium), and iii) with a high quality avatar (high). Participants had to repeatedly activate a virtual lamp and estimate the duration of time intervals as well as judge the passage of time. Our results show a significant effect of embodiment on time perception: time passes slower in the low embodiment condition compared to the medium and high conditions. In contrast to prior work, the study provides missing evidence that this effect is independent of the level of activity of participants: In our task users were prompted to repeatedly perform body actions, thereby ruling-out a potential influence of the level of activity. Importantly, duration judgements in both the millisecond and minute ranges seemed unaffected by variations in embodiment. Taken together, these results lead to a better understanding of the relationship between the body and time.

Abstract: This paper investigates the relationship between perceived object motion and the experience of time in virtual environments. We developed an application to measure how the motion properties of virtual objects and the degree of immersion and embodiment may affect the time experience. A first study (n = 145) was conducted remotely using an online video survey, while a second study (n = 60) was conducted under laboratory conditions in virtual reality (VR). Participants in both studies experienced seven different virtual objects in a randomized order and then answered questions about time experience. The VR study added an "embodiment" condition in which participants were either represented by a virtual full body or lacked any form of virtual body representation. In both studies, time was judged to pass faster when viewing oscillating motion in immersive and non-immersive settings and independently of the presence or absence of a virtual body. This trend was strongest when virtual pendulums were displayed. Both studies also found a significant inverse correlation between the passage of time and boredom. Our results support the development of applications that manipulate the perception of time in virtual environments for therapeutic use, for instance, for disorders such as depression, autism, and schizophrenia. Disturbances in the perception of time are known to be associated with these disorders.

Abstract: In this article, we present a selection of recent studies from our research group that investigated the relationship between time perception and virtual reality (VR). We focus on the influence of avatar embodiment, visual fidelity, motion perception, and body representation. We summarize findings on the impact of these factors on time perception, discuss lessons learned, and implications for future applications. In a waiting room experiment, the passage of time in VR with an avatar was perceived significantly faster than without an avatar. The passage of time in the real waiting room was not perceived as significantly different from the waiting room in VR with or without an avatar. In an interactive scenario, the absence of a virtual avatar resulted in a significantly slower perceived passage of time compared to the partial and full-body avatar conditions. High and medium embodiment conditions are assumed to be more plausible and to less different from a real experience. A virtual tunnel that induced the illusion of self-motion (vection) appeared to contribute to the perceived passage of time and experience of time. This effect was shown to increase with tunnel speed and the number of tunnel segments. A framework was proposed for the use of virtual zeitgebers along three dimensions (speed, density, synchronicity) to systematically control the experience of time. The body itself, as well as external objects, seem to be addressed by this theory of virtual zeitgebers. Finally, the standardization of the methodology and future research considerations are discussed.

Abstract: Joint applications of virtual reality (VR) systems and electroencephalography (EEG) offer numerous new possibilities ranging from behavioral science to therapy. VR systems allow for highly controlled experimental environments, while EEG offers a non-invasive window to brain activity with a millisecond-ranged temporal resolution. However, EEG measurements are highly susceptible to electromagnetic (EM) noise and the influence of EM noise of head-mounted-displays (HMDs) on EEG signal quality has not been conclusively investigated. In this paper, we propose a structured approach to test HMDs for EM noise potentially harmful to EEG measures. The approach verifies the impact of HMDs on the frequency- and time-domain of the EEG signal recorded in healthy subjects. The verification task includes a comparison of conditions with and without an HMD during (i) an eyes-open vs. eyes-closed task, and (ii) with respect to the sensory- evoked brain activity. The approach is developed and tested to derive potential effects of two commercial HMDs, the Oculus Rift and the HTC Vive Pro, on the quality of 64-channel EEG measurements. The results show that the HMDs consistently introduce artifacts, especially at the line hum of 50 Hz and the HMD refresh rate of 90 Hz, respectively, and their harmonics. The frequency range that is typically most important in non-invasive EEG research and applications (<50 Hz) however, remained largely unaffected. Hence, our findings demonstrate that high-quality EEG recordings, at least in the frequency range up to 50 Hz, can be obtained with the two tested HMDs. However, the number of commercially available HMDs is constantly rising. We strongly suggest to thoroughly test such devices upfront since each HMD will most likely have its own EM footprint and this article provides a structured approach to implement such tests with arbitrary devices.

Abstract: Psycho-pathological conditions, such as depression or schizophrenia, are often accompanied by a distorted perception of time. People suffering from this conditions often report that the passage of time slows down considerably and that they are ``stuck in time.'' Virtual Reality (VR) could potentially help to diagnose and maybe treat such mental conditions. However, the conditions in which a VR simulation could correctly diagnose a time perception deviation are still unknown. In this paper, we present an experiment investigating the difference in time experience with and without a virtual body in VR, also known as avatar. The process of substituting a person's body with a virtual body is called avatar embodiment. Numerous studies demonstrated interesting perceptual, emotional, behavioral, and psychological effects caused by avatar embodiment. However, the relations between time perception and avatar embodiment are still unclear. Whether or not the presence or absence of an avatar is already influencing time perception is still open to question. Therefore, we conducted a between-subjects design with and without avatar embodiment as well as a real condition (avatar vs. no-avatar vs. real). A group of 105 healthy subjects had to wait for seven and a half minutes in a room without any distractors (e.g., no window, magazine, people, decoration) or time indicators (e.g., clocks, sunlight). The virtual environment replicates the real physical environment. Participants were unaware that they will be asked to estimate their waiting time duration as well as describing their experience of the passage of time at a later stage. Our main finding shows that the presence of an avatar is leading to a significantly faster perceived passage of time. It seems to be promising to integrate avatar embodiment in future VR time-based therapy applications as they potentially could modulate a user's perception of the passage of time. We also found no significant difference in time perception between the real and the VR conditions (avatar, no-avatar), but further research is needed to better understand this outcome.

Abstract: Biometric measures such as the electroencephalogram (EEG) promise to become viable alternatives to subjective questionnaire ratings for the evaluation of psychophysical effects associated with Virtual Reality (VR) systems, as they provide objective and continuous measurements without breaking the exposure. The extent to which the EEG signal can be disturbed by the presence of VR sys- tems, however, has been barely investigated. This study outlines how to evaluate the compatibility of a given EEG-VR setup on the example of two commercial head-mounted displays (HMDs), the Oculus Rift and the HTC Vive Pro. We use a novel experimental protocol to compare the spectral composition between conditions with and without an HMD present during an eyes-open vs. eyes-closed task. We found general artifacts at the line hum of 50 Hz, and additional HMD refresh rate artifacts (90 Hz) for the Oculus rift exclusively. Frequency components typically most interesting to non-invasive EEG research and applications (<50 Hz), however, remained largely unaffected. We observed similar topographies of visually-induced modulation of alpha band power for both HMD conditions in all subjects. Hence, the study introduces a necessary validation test for HMDs in combination with EEG and further promotes EEG as a potential biometric measurement method for psychophysical effects in VR systems.