What’s the Relationship between Self-Motion Perception and Motion Sickness?

1. 1 What’s the Relationship between Self-Motion Perception and Motion Sickness? L. Scott Urmey Mary E. English Andre McCrimmon *Stephen A. Palmisano Frederick Bonato Andrea Bubka Saint Peter’s College *University of Wollongong Under optokinetic drum conditions, a stationary participant views the patterned interior of a rotating drum and perceives illusory self-motion and sometimes motion sickness. But how exactly are vection and MS related? Experiments using tilted drums and results obtained by others suggest that vection per se does not cause motion sickness. Only Changes in vection velocity and/or heading lead to motion sickness because the sensory conflict is increased only when velocity and/or heading changes occur. EPA, 2005Boston, MA

2. 2 Optokinetic Drum A large drum (cylinder) that rotates around a stationary observer Phenomena Associated with Optokinetic Drums Vection (illusory self-motion)- Usually within 30 seconds observers experience vection (Fischer & Kornmüller, 1930; Tschermak, 1931) in the direction that is opposite to the drum’s true physical rotation. Vection is the self-motion perception that often occurs when a large portion of an observer’s visual field moves. Vection is a useful tool for studying visual field characteristics that affect self-motion perception. Motion Sickness- When optokinetic drum viewing is extended (several minutes) many observers experience motion sickness symptoms. Although motion sickness is commonly associated with passive travel (e.g., carsickness, seasickness, airsickness), stimulus conditions that evoke illusory self motion (e.g., virtual environments, optokinetic drums, large screen cinemas) can also result in motion sickness (e.g., simulator sickness, cybersickness). Motion symptoms can include but are not limited to: dizziness, headache, spinning (vertigo), bodily warmth, increased salivation, stomach awareness, nausea, and dry mouth.

3. lever 0% lever pressure no vection 100% lever pressure saturated vection computer transducer amplifier 3 Measuring Vection Degree of experienced vection, which was recorded for both halves of each trial, was indicated by pressing a lever. As the magnitude of perceived vection increased, the lever was pushed forward. Pressure on the lever was directly recorded by computer for later analysis. % lever pressure 1 0 0 7 5 saturation 5 0 vection onset 2 5 0 0 5 1 0 1 5 3 0 3 5 4 0 4 5 5 0 5 5 6 0 2 0 2 5 seconds Sample output from lever device for measuring vection Measuring Motion Sickness (MS) The symptoms included spinning, dizziness, headache, increased salivation, bodily warmth, stomach awareness, nausea, and dry mouth. Each symptom was rated on a 0-3 scale (0=none, 1=slight, 2=moderate, 3=severe) every two minutes throughout a 16 minute trial. A SSMS (subjective symptoms of motion sickness) composite score was obtained by adding up the ratings for all eight symptoms.

4. 4 Tilted Drum Experiment Hypothesis:Changes in vection due to tilt will lead to a faster onset of MS compared to a drum that rotates on an earth vertical axis. Twelve observers, within-subjects design, drum velocity = 10 rpm, 24 pairs of black and white vertical stripes, independent variable: 0 degree, 5 degree, 10 degree tilt, dependent variable: SSMS (0-3) on 8 symptoms 10o 5o 0o Mean composite SSMS score Minutes of drum exposure Results and Discussion Increasing drum tilt did not affect vection (spinning) ratings. However, the fastest onset of symptoms occurred in the tilt conditions (p<.01). Sensory conflict was the most extreme in the 10 degrees tilt condition. In other words, the 10 degree condition should have resulted in the most disparity between vestibular and visual sensory inputs.These results suggest that an increase in sensory conflict, not vection, are what cause cybersickness to occur in optokinetic drums.These results can be explained in terms of a mismatch between sensed vertical and expected vertical (Bles, Bos, de Graaf, et al., 1998) they can also be explained in terms of a mismatch between sensed inertia and expected inertia. However, the results of the changing rotation direction experiment can only be explained in terms of a mismatch between sensed and expected inertia. The next experiment was designed to test if a mismatch between sensed and expected inertia alone would lead MS.

5. 5 Changing Rotation Direction Experiment Hypothesis:Changes in vection due to rotation direction change will lead to a faster onset of MS compared to a drum that rotates in the same direction. The rationale for this hypothesis is based on the idea that a mismatch between sensed and expected inertia alone can lead to MS. Twelve observers, within-subjects design, drum velocity = 5 rpm, 6 pairs of black and white vertical stripes, independent variable: rotation direction, dependent variable: SSMS (0-3) on 8 symptoms changing dir. Mean composite SSMS score steady rotation 0% vection Minutes of drum viewing Results and Discussion Symptoms occur significantly faster in the changing direction condition (p<.01). Sensory conflict was the most extreme in the changing direction condition. If actual (physical) self-rotation changes took place the vestibular system would respond because of inertia. Results support sensory conflict theory but not subjective vertical mismatch theory. What is happening in terms of vection?

6. 6 General Discussion and Conclusions % lever pressure steady rotation saturated vection saturated less changing vection and less sickness seconds % lever pressure changing direction change continues more changing vection and more sickness seconds • Although vection is often correlated with MS, such as in vehicle simulators and optokinetic drums, vection itself does not cause MS symptoms. • Experiments using drums that are tilted or change direction suggest that changing vection can lead to MS symptoms. Vection that does not change in terms of velocity or heading (steady vection) should theoretically be no different than actual self-motion (as long as the head is immobilized). • Changing vection results in visual/vestibular sensory conflict. Steady vection should not result in sensory conflict. It is sensory conflict that leads to MS and not vection per se. • Although the results of our tilted drum experiments can be explained in terms of a mismatch between sensed vertical and expected vertical (Bles, Bos, de Graaf, et al., 1998) they can also be explained in terms of a mismatch between sensed inertia and expected inertia. However, the results of the changing rotation direction experiment can only be explained in terms of the a mismatch between sensed and expected inertia. Supported by National Science Foundation Grant BCS-0002620