Numerous studies have been conducted to illuminate the effect of image factors to reduce unexpected influence of stereoscopic images on healthy visual experience. In this paper, we introduce changes in the psychological and physiological indexes of observers of a stereo- scopic image disturbed by vibration stimuli. Forty-four healthy university students participated in the experiment. A programmable vibration table generated two types of vibrations (5 Hz and 20 Hz) and provided intermittent vibration stimuli to a stereoscopic projector installed on a vibration table. Our results showed that the frequency of vibration stimuli has a strong impact in evaluating the local comfort of subjects. Our results also showed that the indexes of visual fatigue increased after observation independent of the frequency. The activity status of the autonomic nervous system as a physiological index significantly increased after observing 3D images with vibration stimuli although the vibrational frequency did not have a significant effect on the activity status.
The development of display technologies has made the observation of stereoscopic images more accessible. In recent years, we have been able to enjoy stereoscopic images not only at home but also outdoors using portable video equipment (mobile phones, smartphones, game equipment, etc.). Here, the issue in observing stereoscopic images in such a dynamic environment is unexpected vibration given to the images. Stereoscopic imaging devices input the different images to both eyes according to the horizontal disparity. The visual information processing system in the brain fuses those images to enable the observer to perceive a stereoscopic effect. Thus it is preferable that both the projection system and the observer are in stationary condition. Even under this stationary condition, it is known that comfortable observation of stereoscopic images is inhibited by various factors including unexpected rotation, geometric distortion, vertical shift, horizontal shift, color shift, difference in brightness and so on between left and right eyes [1-11]. It is considered necessary to examine the kind of discomfort that occurs under the condition where both the display and the observer move. Some previous studies examined the comfort or discomfort that vibration stimuli themselves give to the human body [
Only a few studies discussed that the biomedical effect of common 3D movies (dynamic) on observers; Speranza et al. [
In this experiment we presented the observation disturbing factor, which does not exist during typical stereoscopic image observation, by placing a stereoscopic image projector on a vibration table. Two types of vibration stimuli, relatively high (20 Hz) and low (5 Hz) frequencies, were provided to the stereoscopic images. All subjects observed the images provided with two types of vibration stimuli in random order, taking approximately a one-hour break between the two observations. Two types of psychological reactions and one physiological reaction were measured while the subjects observed an approximately twenty-minute stereoscopic movie. The psychological reaction was measured using a questionnaire (SSQ, [
Forty-four male and female university students (average age: 22.36 ± 1.78 years old) participated in the experiment. All subjects received payment for their participation. The subjects did not know the purpose of the experiment. Written consent was obtained from each subject for participation in the experiment before starting the study. The details of experiment were approved by the Human Engineering Ethics Committee.
The experiment used commercially available Blu-ray disc software for a marine documentary movie (Deep Sea, Warner Home Video). The movie was reproduced using a Blu-ray disc player (BDP-S470, SONY) and projected shown onto a hundred-inch screen using a 3D projector (VPL-VW90ES, SONY) based on a liquid crystal shutter glasses method. Sound was provided to subjects through headphones from the Blu-ray disc player. A 3D projector was set on a vibration table (BF-50UT, IDEX,
The experiment was conducted in a darkened room. After attaching the electrodes for the electrocardiogram, subjects sat at a distance of 3.74 m from the screen. This distance complies with a guideline for maintaining comfort when observing stereoscopic movies [
The subjects were asked to complete a simulator sickness questionnaire (SSQ) before and after viewing the twenty-minute movie as one of the psychological evaluations on a stereoscopic movie. The SSQ questionnaire consisted of 18 questions and four choices of answers (none, slight, moderate, severe) on movie sickness. The internal status of the observer can be outlined in three categories (nausea, eye fatigue and disorientation) and total scores by placing a specified weight on the raw score.
A direct evaluation of comfort while observing the stereoscopic movie on a five-level scale (very uncomfortable, rather uncomfortable, neither, rather comfortable, very comfortable) was conducted as the other psychological evaluation. The subjects indicated their subjective evaluation in response to a beep sound every 2 minutes and 30 seconds from 10 seconds after the start of movie using a switchbox with five channels placed on their knees.