Hiroyasu Ujike

Effects of visually simulated roll motion on vection and postural stabilization

BackgroundVisual motion often provokes vection (the induced perception of self-motion) and postural movement. Postural movement is known to increase during vection, suggesting the same visual motion signal underlies vection and postural control. However, self-motion does not need to be consciously perceived to influence postural control. Therefore, visual motion itself may affect postural control mechanisms. The purpose of the present study was to investigate the effects of visual motion and vection on postural movements during and after exposure to a visual stimulus motion.MethodsEighteen observers completed four experimental conditions, the order of which was counterbalanced across observers. Conditions corresponded to the four possible combinations of rotation direction of the visually simulated roll motion stimulus and the two different visual stimulus patterns. The velocity of the roll motion was held constant in all conditions at 60 deg/s. Observers assumed the standard Romberg stance, and postural movements were measured using a force platform and a head position sensor affixed to a helmet they wore. Observers pressed a button when they perceived vection. Postural responses and psychophysical parameters related to vection were analyzed.ResultsDuring exposure to the moving stimulus, body sway and head position of all observers moved in the same direction as the stimulus. Moreover, they deviated more during vection perception than no-vection-perception, and during no-vection-perception than no-visual-stimulus-motion. The postural movements also fluctuated more during vection-perception than no-vection-perception, and during no-vection-perception than no-visual-stimulus-motion, both in the left/right and anterior/posterior directions. There was no clear habituation for vection and posture, and no effect of stimulus type.ConclusionOur results suggested that visual stimulus motion itself affects postural control, and supported the idea that the same visual motion signal is used for vection and postural control. We speculated that the mechanisms underlying the processing of visual motion signals for postural control and vection perception operate using different thresholds, and that a frame of reference for body orientation perception changed along with vection perception induced further increment of postural sway.

Survey on motion sickness-like symptoms provoked by viewing a video movie during junior high school class

Abstract The incident of visually induced motion sickness (VIMS) occurred with a 20-min video movie during class in a local junior high school in Japan in 2003. To investigate possibly contributing factors of VIMS, we collected the incident data in three ways: interviewing school officials, measuring the visual environment on site, and surveying by questionnaires to the students. Analyzing the collected data showed that the students’ severities of the sickness related with their viewing distance to the video image, their concentrations on the video movie, their getting a cold, and their daily playing hours of video games. The results indicated that individual differences are determined not only by one factor, like autonomic nervous activity often focused in the literature, but also by combinations of other personal factors, such as health conditions, watching attitudes, and daily play activities.

Motion parallax driven by head movements: conditions for visual stability, perceived depth, and perceived concomitant motion.

Yoking the movement of the stimulus on the screen to the movement of the head, we examined visual stability and depth perception as a function of head-movement velocity and parallax. In experiment 1, for different head velocities, observers adjusted the parallax to find (a) the depth threshold and (b) the concomitant-motion threshold. Between these thresholds, depth was seen with no perceived motion. In experiment 2, for different head velocities, observers adjusted the parallax to produce the same perceived depth. A slower head movement required a greater parallax to produce the same perceived depth as faster head movements. In experiment 3, observers reported the perceived depth for different parallax magnitudes. Perceived depth covaried with smaller parallax without motion perception, but began to decrease with larger parallax and concomitant motion was seen. Only motion was seen with the larger parallax.

Estimation of Visually Induced Motion Sickness from Velocity Component of Moving Image

The purpose of the study is to examine whether the effects of global motion, (GM), on visually induced motion sickness, (VIMS), found with visual stimulus consisting of simple global motion will be applied to the effects of moving images including combination of global motion on VIMS. We, previously, found that velocity, but not temporal frequency component, of GM dominates subjective scores related to VIMS in the experiments presenting simple GM. To achieve the purpose, I made a model to estimate discomfort level of a standard observer during watching a moving image. The model, at the beginning, analyses GM included in the movie; and then, the time-series of velocity data in each element of analyzed GM is compared with the characteristics of simple GM on VIMS for estimating discomfort level. The validity of the model was examined by comparing the estimated discomfort level and actually measured average discomfort level using identical video movie which rather easily inducing VIMS. As a result, the model well estimates the values of subjective score actually measured during observers watching video movies.

Influence of 3‐D cross‐talk on qualified viewing spaces in two‐ and multi‐view autostereoscopic displays

— To estimate the qualified viewing spaces for two- and multi-view autostereoscopic displays, the relationship between image quality (image comfort, annoying ghost image, depth perception) and various pairings between 3-D cross-talk in the left and right views are studied subjectively using a two-view autostereoscopic display and test charts for the left and right views with ghost images due to artificial 3-D cross-talk. The artificial 3-D cross-talk was tuned to simulate the view in the intermediate zone of the viewing spaces. It was shown that the stereoscopic images on a two-view autostereoscopic display cause discomfort when they are observed by the eye in the intermediate zone between the viewing spaces. This is because the ghost image due to large 3-D cross-talk in the intermediate zone elicits different depth perception from the depth induced by the original images for the left and right views, so the observers depth perception is confused. Image comfort is also shown to be better for multi-views, especially the width of the viewing space, which is narrower than the interpupillary distance, where the parallax of the cross-talking image is small.

Subjective staircase: A multiple wallpaper illusion

When observers binocularly fixate on an inclined sheet of paper with equally spaced dots, an apparent “staircase” is seen. We varied the inclination of the sheet, the spacing among the dots, and the viewing distance. The results indicate that (1) as the space and the inclination decreased, the number of apparent steps increased and the height of apparent steps decreased, and (2) as the distance and the inclination increased, the number of apparent steps decreased, and eventually the illusion disappeared. The nearest-neighbor rule and the extent of the vertical horopter inclination explain the characteristics of the illusion.

Visual rotation axis and body position relative to the gravitational direction: Effects on circular vection

The visual–vestibular conflict theory asserts that visual–vestibular conflicts reduce vection and that vection strength is reduced with an increasing discrepancy between actual and expected vestibular activity. Most studies support this theory, although researchers have not always accepted them. To ascertain the conditions under which the theory of the visual–vestibular conflict can be applied, we measured circular vection strength accompanied by manipulation of the visual–otolith conflict by setting the axes of visual global motion (pitch, roll, and yaw) as either earth-horizontal or earth-vertical, using three different body positions (supine, left-lateral recumbent, and sitting upright). When the smaller stimulus was used, roll vection strength was greater with the visual–otolith conflict than without it, which contradicts the visual–vestibular conflict theory. We confirmed this result, as observers were able to distinguish circular vection from an illusory body tilt. Moreover, with observers in an upright position, the strength of yaw vection, which does not involve the visual–otolith conflict, increased and was almost equal to that of roll vection, which involves the visual–otolith conflict. This suggests that if the visual stimulus covers the entire visual field, the strength of circular vection around the earth-vertical axis exceeds that around the earth-horizontal axis, which is a finding consistent with the visual–vestibular conflict theory.

The Activity of ISO/Study Group on Image Safety and Three Biological Effect

International guidelines to reduce biomedical effects caused by moving images are being developed. Activities related to the standardization of image safety are presented. Measurement methods and scientific knowledge concerning three major biomedical effects of moving images and the authors¿ data on visually induced motion sickness data were introduced.

Relative distance cues contribute to scaling depth from motion parallax

The visual system scales motion parallax signals with information about absolute distance (M. E. Ono, Rivest, & H. Ono, 1986). The present study was designed to determine whether relative distance cues, which intrinsically provide information about relative distance, contribute to this scaling. In two experiments, two test stimuli, containing an equal extent of motion parallax, were presented simultaneously at a fixed viewing distance. The relative distance cues of dynamic occlusion and motion parallax in the areas surrounding the test stimuli (background motion parallax) and/or relative size were manipulated. The observers reported which of the two parallactic test stimuli appeared to have greater depth, and which appeared to be more distant. The results showed that the test stimulus specified, by the relative distance cues, as being more distant was perceived as having more depth and as being more distant. This indicates that relative distance cues contribute to scaling depth from motion parallax by modifying the information about the absolute distance of objects.

Transformation of the visual-line value in binocular vision: stimuli on corresponding points can be seen in two different directions.

We examined Wheatstones (1838 Philosophical Transactions of the Royal Society of London 128 371–394) claim that images falling on retinally corresponding points can be seen in two different directions, in violation of Herings law of identical visual direction. Our analyses showed that random-dot stereograms contain stimulus elements that are conceptually equivalent to the line stimuli in the stereogram from which Wheatstone made his claim. Our experiment demonstrated that two lines embedded in a random-dot stereogram appeared in two different directions when they stimulated retinally corresponding points, if the disparity gradient value of the lines was infinity relative to adjacent elements. To ensure that the two lines stimulated corresponding points, observers made vergence eye movements while maintaining the perception of the two lines in two different directions.