There were 21 adult volunteers (15 male, 6 female). Four reported more than 10 minutes prior experience with virtual environments. The participants are summarized in Table 6.5.
None had participated in Experiment AIIIE1. Participant screening was done more rigorously than in Experiment AIIIE1. Participants were asked whether they were over 18, had had alcohol or drugs in the last 24 hours, had any color-blindness, were checked for flat-soled shoes, asked about current sickness or sickness in the last week, whether they had a history of epilepsy or any uncorrected visual/vestibular problems, and were checked for 20/25 or better visual acuity.
Id is the participant number. Gn gives the gender, Age the age in years, and Prev is ``1'' if the participant had more than 10 minutes of prior experience in virtual environments, ``0'' otherwise.
The methods for Experiment AIIIE2 were similar to Experiment AIIIE1, with the refinements described below.
For Experiment AIIIE2, a second videotape was made, similar in all respects to the first except that a performance task was added to force attention into the CI. Two colleagues, who were separated by 180, each held up a large sheet of posterboard. Each posterboard was white on one side and either bright green or bright red on the other. When the camera swept by, each colleague displayed the white side approximately 75% of the time, and the colored side the other 25% of the time, with a random pattern. Participants were asked to call out the color when a colored sign appeared in the videotape. Responses were recorded on audiotape to check task performance.
Instructions to participants included the following:
You will wear a Virtual i-O HMD for this experiment. The HMD will show a rotating scene. Red and green signs will be displayed periodically; your task will be to call out ``red'' or ``green'' when you see a ``red'' or ``green'' sign. You will be asked to stand in the Sharpened Romberg stance for one minute while viewing the image. (It's okay if you need to break the Sharpened Romberg stance; just get back into it.) You will then have one minute to relax while viewing the rotating image, followed by 1 minute more in the Sharped Romberg stance, then a minute and a half to relax while viewing the rotating image.
In addition to the three dependent measures used in Experiment AIIIE1 (stance breaks, SSQ and reported vection), pre- and post-exposure ataxia were recorded. The pre- and post-exposure ataxia measures were made with a Chattecx Balance System (see Section 3.7.5). Postural measurements were taken with subjects in the Sharpened Romberg stance with eyes open.
The average of three trials on the Balance System prior to each condition was used as the baseline ataxia measure. The average of two trials on the Balance System after each condition was used as the post-exposure ataxia measure. (As the intent was to test for rapidly-decaying after-effects, it was not thought that more than two post-exposure readings would be useful.) Measurements were taken with participants in the Sharpened Romberg stance with eyes open. Prior to each measure, participants mounted the apparatus and were given a few seconds to attain their balance. Participants stepped off the apparatus and stood at ease for approximately 30 seconds between trails while the results were calculated. Post-exposure measures were recorded immediately after exposure. Participants were asked to close their eyes while the HMD was removed, then open their eyes and walk directly to the Balance System, located a couple of steps away.
Exposure in each condition was for 4.5 minutes, with the first and third minutes in Sharpened Romberg. The extra 1.5 minutes at the end compared to Experiment AIIIE1 was intended to increase the chance of finding an ataxia after-effect. There was a 15 minute break between conditions, during which subjects relaxed and walked around the building to mitigate any carryover effects between conditions.
Head rolls were removed, both to reduce individual variations in how the rolls were performed and for fear that with attention forced into the spinning CI, motion sickness and ataxia might otherwise be too large.
The design of the HMD masking was improved to remove a slight breathing restriction, which might have elevated SSQ ratings over both conditions in Experiment AIIIE1.
The visibility-of-the-background rating was changed to a 1-7 scale in Experiment AIIIE2, for consistency with the vection scale and prior work.
The Balance System was also used to check that participants were back to their baseline level of postural stability before leaving the experiment.