Self-motion perception is explored in several different ways at the Max Planck Institute for Biological Cybernetics. First, the perception of self-motion while moving through a space is investigated from a multi-sensory integration perspective looking at the contributions of visual, vestibular, and proprioceptive information. A second focus is on investigations of the illusion of self-motion - that is, how can we fool the user into believing that they are moving without having expensive technology to actually move them. Finally, self-motion perception during walking is studied with the specific aim of better simulating walking within an infinite plane through the development and testing of an omni-directional treadmill.

◘ Human locomotion and gait parameters
◘ Perception of self-motion in Virtual Reality
◘ Spatial updating during movement in two and three dimensions
◘ Perception and production of speed during self-motion
◘ Bayesian integration of visual and vestibular information
◘ Vection in a Large Screen Immersive Virtual Environment
◘ Vestibular Direction Detection Thresholds in the Horizontal Plane

Vection in a Large Screen Immersive Virtual Environment

The illusion of self motion perception, generally known as vection has been investigated from a psychological perspective since 1875. Vection can occur naturally when in a stationary vehicle and observing a moving, adjacent object such as when sitting in a train and observing an adjacent train begin to move. Studying vection can provide insights into how sensory information is integrated in the brain as well as a means to improve the design of existing applications such as driving simulations and entertainment park rides.

Our aim is to examine the visual factors that affect the perception of illusory self motion in a large screen immersive virtual environment. Among the factors investigated are, the direction of movement, the vertical field of view and the attention of the observer.

In an initial study we investigated how the direction of motion specified by optic flow affects the perception of self motion. We also studied the effect the floor projection (which significantly increases the field of view in our current setup: See Figure 1) has on the effectiveness of the illusion. Twelve trajectories of motion, varying by motion direction, were presented to seated, stationary users and consisted of a random dot limited lifetime particle system. An additional condition evaluated a limited subset of these motion trajectories in a photorealistic environment (Virtual Tübingen ? see Figure 2) [1, 2].

Figure 1: Large screen virtual environment setup with a field of view of 220
degrees horizontal by 165 degrees vertical. Four JVC D-ILA DLA-SX21S video
projectors with a resolution of 1400 X 1050 pixels were used to display visual
stimuli on the front, sides and floor.

In a second study we evaluated the effect of two visual attention tasks on the perception of linear vection. All participants experienced three conditions: baseline (no attention task), visual attention (react to viewing one particular target), and working memory (count a subset of specific targets) [3]. In all conditions the virtual environment consisted of a tunnel-like scene and participants fixated on the center of the screen while targets appeared moving on the ground floor (see Figure 1).

Figure 2: Visual stimuli used to induce vection consisting of a
photorealistic virtual environment model of the town of Tübingen

In the first set of experiments, lower vection onset times were reported for backward, downward, circular, and curvilinear motions than for forward, sideways, and upward motions. Also, in the photorealistic environment we found that linear vection was improved (lower onset time) with a floor projection while circular vection was not affected.

The attention task was found to have a significant effect on vection onset time with a decrease from a mean of 10.23 seconds (baseline condition) to a mean of 7.81seconds (working memory condition).

Future research will further investigate the effect of an individual?s attention on the illusory sensation of self-motion. We will do this by altering the cognitive load of an individual in systematic ways and determining the impact of this cognitive load on subjective ratings of vection.

REFERENCE

◘ Trutoiu, L. C., B. Mohler, J. Schulte-Pelkum and H.H. Bülthoff: Circular, Linear, and Curvilinear Vection in a Large-screen Virtual Environment with Floor Projection. IEEE Virtual Reality 2008, 115-120 (03/08/ 2008)

◘ Trutoiu, L. C., Streuber, S., Mohler, B. J., Schulte-Pelkum, J., and Bülthoff, H.H.: Tricking people into feeling like they are moving when they are not paying attention. , In Proceedings of the 5th Symposium on Applied Perception in Graphics and Visualization (Los Angeles, California, August 09 - 10, 2008)