Color/Contrast Effects on Motion Sickness in an Optokinetic Drum
The goal of the current experiment was to test the effect of chromaticity on MS. It was hypothesized that chromaticity would hasten the onset of MS in an optokinetic drum. No previously published studies have systematically focused on the role of color on MS symptoms. A more detailed description of this experiment can be found in the following article: Bonato, F., Bubka, A., & Alfieri, L. (2004). Display color affects motion sickness onset in an optokinetic drum. Aviation, Space, and Environmental Medicine, 75, 306-311.
Participants- Twelve individuals voluntarily participated in the experiment (4 males, 8 females). Potential participants who reported no history of motion sickness susceptibility were not allowed to participate in the experiment. Persons reporting any visual, vestibular, neurological, or gastrointestinal abnormality, or any other general health problem, were not allowed to participate. Participants fasted for at least 2 hours before each experimental trial. The study protocol was approved in advance by the Saint Peter’s College Institutional Review Board. Each subject provided written informed consent before participating.
Apparatus- The optokinetic drum consisted of a synthetic composite cylinder 122 cm in height and 107 cm in diameter. The drum was suspended from a motor attached to a beam directly above the drum with two steel cables. Head position was maintained throughout the experiment by means of an optical chin rest. Viewing took place from the drum’s center resulting in a viewing distance of 53.5 cm when the participant’s line of sight was perpendicular to the drum’s surface. Horizontally positioned baffles attached to the top and bottom of the chin rest restricted the participant’s view so that the only surface seen through the baffles was the interior of the drum. Illumination was provided by two 32-W florescent bulbs positioned directly behind a translucent plastic diffuser panel and 102 cm directly above the top of the drum.
Stimulus Displays- The three stimulus displays are shown above. Each display consisted of 12 vertical stripes that lined the optokinetic drum. The width of each stripe subtended 30° wide of visual angle. One condition consisted of alternating black and white stripes having luminance values of 1.6 and 36.0 cd/m2 respectively. In addition to black and white stripes (two each) the gray shade condition consisted of four different shades of gray stripes—two for each shade. The four gray shades had luminance values of 6.6, 10.5, 11.9, and 24.6 cd/m2. In addition to black and white stripes (two each), the chromatic condition consisted of four different color stripes, two each of the following: red, blue, green, yellow, black, and white. The luminance value of each stripe in the gray shade condition was matched as closely as possible with the luminance value of one of the stripes in the chromatic condition.
Subjective Symptoms of Motion Sickness Scale- A SSMS scale was used to assess eight subjective symptoms of motion sickness (SSMS). Each symptom was rated by the participant using a 0-3 scale (0=none, 1=mild, 2=moderate, 3=severe). The symptoms rated were spinning, dizziness, bodily warmth, headache, increased salivation, stomach awareness, nausea, and dry mouth. Unlike a study that involves assessing participants’ symptoms pre and post treatment1, in the present study we wanted to track the development of symptoms throughout the course of each trial. In order to do so, ratings were obtained from each participant every two minutes. Therefore a simplified scale was needed so that participants could provide ratings quickly.
Procedure and Design- The participant sat inside the stationary drum and was familiarized with the SMSS scale. Baseline SSMS ratings were obtained at the beginning of each trial. The participant was instructed to close their eyes until the drum steadily rotated at a speed of 30°/sec (5 RPM). The participant was then instructed to open their eyes and SSMS ratings were obtained every two minutes throughout the trial (up to 16 minutes).Each participant served in all three conditions: 1) black and white stripes, 2) gray stripes, and 3) chromatic stripes. Participation was completely counterbalanced. At the conclusion of each trial, the participant rested until the severity of their symptoms subsided. The participant was scheduled for a subsequent condition in 48-72 hours.
Results- A composite SSMS score was calculated for each participant by adding the subjective ratings (0-3) for each of the eight symptoms probed (spinning, dizziness, bodily warmth, headache, increased salivation, stomach awareness, nausea, and dry mouth). The mean number of minutes to reach the approximate midpoint of the SSMS scale (11) in the black and white, gray shade, and chromatic conditions were 8.7, 7.8, and 5.2 minutes. A one-way repeated measures ANOVA revealed a significant difference among conditions, [F(2, 22)=5.5, p<.011]. Out of the eight symptoms probed in the present study, three can be considered major: dizziness, headache, and nausea. The mean SSMS ratings (0=none, 1=slight, 2=moderate, 3=severe) for dizziness, headache, and nausea attained at the four-minute mark were calculated for the black and white, gray shade, and chromatic conditions. Four minutes was chosen because the data from all the participants except for one was available.
The means obtained for dizziness were 0.91, 1.36, and 1.73 respectively for the black and white, gray shade, and chromatic conditions. A one-way repeated measures ANOVA revealed a significant difference among conditions for dizziness [F(2, 20)=4.8, p<.019]. The means obtained for headache were 0.27, 0.64, and 1.1 respectively for the black and white, gray shade, and chromatic conditions. A one-way repeated measures ANOVA revealed a significant difference among conditions for headache [F(2, 20)=5.3, p<.014]. The means obtained for nausea were 0.27, 0.36, and 0.91 respectively for the black and white, gray shade, and chromatic conditions. A one-way repeated measures ANOVA did not reveal a significant difference among conditions for nausea.
Discussion- The results of the current experiment clearly indicate that the addition of chromaticity to an optokinetic drum lining significantly affects MS onset and severity. In the chromatic condition MS onset was faster and symptoms more severe compared to the other two conditions. Two major MS symptoms, dizziness and headache, were found to both be significantly worse in the chromatic condition. Comparing these subjective ratings at four minutes into each trial, it was found that the mean dizziness rating in the chromatic condition was nearly twice as high as the rating in the black and white condition. Likewise, the mean headache rating found in the chromatic condition was approximately four times as high as that found in the black and white condition.
The results of our color vection experiment and the color MS experiment agree with results obtained by other investigators that suggest vection and MS symptoms are correlated under some conditions. It would however be wrong to assume that vection causes MS. For some individuals, vection is experienced but MS symptoms never develop. This is true for labyrinthine-defectives, individuals who have nonfunctioning vestibular systems. It is not vection per se that causes MS, but more likely the sensory conflict that often accompanies some types of vection. Such a situation typically occurs under optokinetic drum conditions. In a rotating drum, visual input indicates that self-rotation is occurring but the vestibular system provides information that the participant is stationary. It stands to reason that increases in the vection magnitude would be accompanied by increases in the magnitude of disparity between visual and vestibular inputs. In terms of the current results the following analysis seems to apply: 1) the addition of chromaticity to the stimulus increased the vection magnitude, 2) the disparity between vestibular and visual inputs increased, and 3) the onset of MS symptoms for susceptible individuals was hastened.
The question of why the addition of chromaticity should increase vection magnitude is more difficult to answer. Adding chromatic changes in the stimulus displays may lead to greater field stability, the percept that the visual field is stationary even if it is in fact moving. The result of increased field stability is an increase in the magnitude of vection. We suggest here that any increases in the complexity of the visual field will tend to lead to an increase in field stability. Any Increase in scene complexity will tend to make the stimulus pattern more like the real world in which our visual system evolved, a world that is generally perceived to be “unmoving.”
Bonato, F., Bubka, A., & Alfieri, L. (2004). Display color affects motion sickness onset in an optokinetic drum. Aviation, Space, and Environmental Medicine, 75, 306-311.
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