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I've ridden a virtual roller coaster on an Oculus Rift. I felt tension as I went up to the top, but more interestingly I actually felt my stomach drop when I went down the steep drop on the other side. Why can I feel this, when no forces are actually being applied to my stomach?

A bonus question: If you took someone that had never ridden a roller coaster, or even been exposed to rapid acceleration, and had them try a virtual one - would they feel the same stomach lurch as I did?

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Why can I feel this, when no forces are actually being applied to my stomach?

Acceleration sensors are in the ears and are part of the vestibular system. The vestibular nuclei in the brain uses acceleration- and visual signals to decide what happens to your body. It can be fooled by visual signals without the presence of acceleration signals. The role of the vestibulo-autonomic reflex - you feel in your stomach - is probably to protect your inner organs from the damage they can possibly suffer by acceleration.

The same can happen by watching films with fast camera movements on a monoscopic display (e.g. normal films in the cinema or video games on an average LCD monitor, etc...), however not so often than by stereoscopic displays (e.g. 3d films in the cinema, stereoscopic video games on a head-mounted display like Oculus Rift, etc...). This is because stereoscopic displays create the perfect illusion of depth (e.g. they can even be used by a therapy to overcome acrophobia), while monoscopic displays don't. So your vestibular nuclei is fooled much easier by stereoscopic displays.

References:

These data show that a subset of PBN/KF neurons, whose activity is altered by a nauseogenic stimulus also respond to body motion and that irritation of the stomach lining can either cause an amplification or reduction in the sensitivity of the units to vestibular inputs. The findings imply that nausea and affective responses to vestibular stimuli may be modified by the presence of emetic signals from the GI system.

This study describes the relation between the vection produced by optical flow and that created by galvanic vestibular stimulation. Vection is the illusion of self motion and is most often experienced when an observer views a large screen display containing a translating pattern. This illusion has only limited fidelity and duration unless it is reinforced by confirming vestibular information. Galvanic vestibular stimulation (GVS) can directly produce the sensation of vection.

Neurons in the vestibular nuclei are not only activated by vestibular signals, but also by visual information. Consequently, the sensations of body motion derived from visual and vestibular signals are indistinguishable.

Sensations of body movement can also be generated by visual signals arriving at the vestibular nuclei. During unnatural movements of the body, conflict between visual and vestibular information leads to disorientation and nausea, as in the oculogyral illusion, the Coriolis effect, and vection.

Three-dimensional movies presented via stereoscopic displays have become more popular in recent years aiming at a more engaging viewing experience. However, neurocognitive processes associated with the perception of stereoscopic depth in complex and dynamic visual stimuli remain understudied. Here, we investigate the influence of stereoscopic depth on both neurophysiology and subjective experience. Using multivariate statistical learning methods, we compare the brain activity of subjects when freely watching the same movies in 2D and in 3D. Subjective reports indicate that 3D movies are more strongly experienced than 2D movies. On the neural level, we observe significantly higher intersubject correlations of cortical networks when subjects are watching 3D movies relative to the same movies in 2D. We demonstrate that increases in intersubject correlations of brain networks can serve as neurophysiological marker for stereoscopic depth and for the strength of the viewing experience.

Statistical differences in theta activity showed that the real and 3D environments caused similar cognitive processes, while the 2D caused an increase of anxiety indicating that perhaps participants were looking for the third dimension. Beta and gamma activity showed that participants perceived the third dimension of the stereoscopic environment as in the real one, something that did not happen in the 2D environment. Our findings indicate that stereoscopic 3D virtual environments seem to approximate the real ones as far as it regards the cognitive processes they cause. Three dimensional stereoscopic environments increase users’ attention over the 2D and cause less mental effort.

In this study the effects of virtual reality exposure therapy (VRET) were investigated in patients with acrophobia. Feelings of presence in VRET were systematically varied by using either a head-mounted display (HMD) (low presence) or a computer automatic virtual environment (CAVE) (high presence). VRET in general was found to be more effective than no treatment. No differences were found in effectiveness between VRET using an HMD or CAVE. Results were maintained at 6 months follow-up. Results of VRET were comparable with those of exposure in vivo (Cyberpsychology and Behavior 4 (2001) 335). In treatment completers no relationship was found between presence and anxiety. Early drop-outs experienced less acrophobic complaints and psychopathology in general at pre-test. They also experienced less presence and anxiety in the virtual environment used in session one as compared to patients that completed VRET.

Despite the increasing use of virtual reality, the impact on cerebral representation of topographical knowledge of learning by virtual reality rather than by actual locomotion has never been investigated. To tackle this challenging issue, we conducted an experiment wherein participants learned an immersive virtual environment using a joystick. The following day, participants' brain activity was monitored by functional magnetic resonance imaging while they mentally estimated distances in this environment. Results were compared with that of participants performing the same task but having learned the real version of the environment by actual walking. We detected a large set of areas shared by both groups including the parieto-frontal areas and the parahippocampal gyrus. More importantly, although participants of both groups performed the same mental task and exhibited similar behavioral performances, they differed at the brain activity level. Unlike real learners, virtual learners activated a left-lateralized network associated with tool manipulation and action semantics. This demonstrated that a neural fingerprint distinguishing virtual from real learning persists when subjects use a mental representation of the learnt environment with equivalent performances.

Our main results are (1) stereoscopy in games increased experienced immersion, spatial presence, and simulator sickness; (2) the eff ects strongly differed across the three games and for both ge nders, indicating more affect on male users and with games involving depth animations; (3) results related to attention and cognitive involvement indicate more direct and less thoughtful interactions with stereoscopic games, pointing towards a more natural experience through stereoscopy.

The results indicate that in a 2D movie viewers tended to look at the actors, as most of the eye movements were clustered there. The significance of the actors started at the beginning of a shot, as the eyes of the viewer focused almost immediately to them. In S3D movie the eye movement patterns were more widely distributed to other targets. For example, complex stereoscopic structures and objects nearer than the actor captured the interest and eye movements of the participants. Also, the tendency to first look at the actors was diminished in the S3D shots.

For the correlation between anxiety and presence, the results show very low correlation between anxiety and presence.

Stereoscopic visualization in cinematography and VR creates an illusion of depth by means of two bidimensional images corresponding to different views of a scene. This perceptual “trick” is used to enhance the emotional response and the sense of presence and immersivity of the observers. An interesting question is if and how is possible to measure and analyze the level of emotional involvment of the observers during a stereoscopic visualization of a movie or of a virtual environment. The final goal of this research is a challenge, due to the large number of sensorial, physiological and cognitive stimuli involved. In this paper we begin this research by analyzing eventual differences in the brain activity of subjects during the observation of monoscopic or stereoscopic contents. To this aim, we have performed some experiments collecting EEG data using a Brain-Computer Interface device from two groups of users, during the observation of stereoscopic and monoscopic short movies inside the Virtual Theater of the University of Milan. From the analysis of the collected data, it seems that interesting differences are present in the average brain activity among the observers in the two groups, with a significative effect of stereoscopic visualization.

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If you took someone that had never ridden a roller coaster, or even been exposed to rapid acceleration, and had them try a virtual one - would they feel the same stomach lurch as I did?

Probably not. A congenitally blind person, who can distinguish between a globe and a cube by her touch, is not able to tell which one is which (without touching) when given sight. For details see the article "The newly sighted fail to match seen with felt" from Nature: http://www.nature.com/neuro/journal/v14/n5/abs/nn.2795.html.

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