The Role of Rest Frames in Vection, Presence and Motion Sickness.

by Jerrold Prothero

Chapter to be published in forthcoming book:
L. Hettinger and M. Hass (Eds). Psychological Issues in the Design and the Use of Adaptive, Virtual Interfaces

Abstract

Two fundamental issues facing the virtual interface community are avoiding motion sickness and developing robust measures for the goodness of virtual interfaces (in terms of their intuitiveness and their ability to convey meaning). Both of these issues go to the core of human psychology; hence it is unlikely that they can be addressed effectively except through a fundamental psychological theory. Synthesizing prior work in many areas of perception, such a theory is put forward.

Literature is reviewed indicating that presence, the sense of "being in" a virtual interface, is related to the intuitiveness and meaningfulness of the interface. Therefore, Class A ("objective") presence measures are potentially useful to evaluate these aspects of virtual interfaces.

The following two hypotheses are advanced, which suggest that presence plays a deep role in perception, and is closely related to specific visual illusions, as well as to motion sickness.

• Rest Frame Hypothesis. The nervous system has access to many rest frames. Under normal conditions, one of these is selected by the nervous system as the comparator for spatial judgments. We call this the "selected rest frame" (SRF). Under some conditions, the nervous system is not able to select a single rest frame.
• Presence Hypothesis. The sense of presence in an environment reflects the degree to which that environment influences the SRF.

These hypotheses suggest three areas of research. Prior and future work in each of these areas is described.

Area I. Presence reflects SRF decisions.

This suggests "Class A" measures for presence based on creating a conflict between virtual and real rest frame cues and measuring their relative influence on perception.

Area II. Which stimuli influence SRF choices?

The nervous system uses particular cues from the environment to select a rest frame. By manipulating these cues, it is possible to affect the sense of presence in a virtual environment. (There are also potential applications to facilitating task performance by communicating particular rest frames, for instance in the context of collaborative work in weightlessness.)

Area III. What happens when the SRF is inconsistent with some motion cues?

A. The SRF is dominated by visual cues.

B. No SRF is formed.

A. Suggests links between presence and various illusion such as vection, induced motion, perceived tilt and distance illusions, all of which can be categorized in terms of how they might arise from rest frame disturbances. The common themes between them are summarized (for a brief discussion, see Appendix).

B. Suggests links between presence, motion sickness, and the illusions mentioned in "A". Hence, techniques can be borrowed from the literature on these illusions to address motion sickness, and in particular the form which occurs in simulators.

Appendix

SRF's are hypothesized to determine one's sense of position, angular orientation and motion: both for oneself and for objects in the environment. This implies that SRF failures should result in illusions of position, orientation, and motion.

We would expect the visual background to play an important role in determining the SRF, since the visual background in general provides the largest set of self-consistent motion cues in the environment.

If we consider the crossing of ``self'' or ``external objects'' with ``position'', ``orientation'' or ``motion'', we would predict that six types of illusions should be possible by altering the SRF through visual background manipulations. The six possiblities are itemized below.

• Self and Motion. The visually-induced perception of self-motion is called ``vection''. Recent work implies that vection is heavily influenced by one's relative motion with respect to the perceived visual background (Brandt et al., 1975; Ohmi et al., 1987; Ohmi & Howard, 1988).
• External Objects and Motion. If one moves the background behind an object, one often has the impression that the object is moving in the opposite direction to the background. This is called ``induced motion'' (Wallach, 1959).
• Self and Orientation. If one is placed in a room in which the walls are tilted, one tends to perceive that one is tilted in the opposite direction. (Howard, 1986).
• External Objects and Orientation. A tilted background can alter one's perception of the orientation of an object in the foreground with respect to gravity (Howard, 1986).
• Self and Position. We suggest that presence, the sense of ``being somewhere'', encompasses this kind of illusion.
• External Objects and Position. Visual background manipulations may alter the perceived distance to objects, which is a form of position illusion. An example of this is the corridor illusion (Levine & Shefner, 1991).

References

Brandt, T., Dichgans, J. & Koenig, E. (1975). Foreground and background in dynamic spatial orientation. Perception & Psychophysics 17, 497-503.

Howard, I. (1986). The perception of posture, self motion, and the visual vertical. In Handbook of Perception and Human Performance. New York, NY: John Wiley & Sons.

Levine, M. & Shefner, J. (1991). Fundamentals of Sensation and Perception. Pacific Grove, CA:Brooks/Cole Publishing Company.

Ohmi, M., Howard, I.P. & Landolt, J.P. (1987). Circular vection as a function of foreground-bakcground relationships. Perception, 16, 17-22.

Ohmi, M. & Howard, I.P. (1988). Effect of stationary objects on illusory forward self-motion induced by a looming display. Perception, 17, 5-12.

Wallach, H. (1959). The perception of motion. Scientific American, July.