Kazuki Yoshikawa

Effect of Accommodation Training on Visual Function of Visual Inspection Workers and Middle-Aged People

By relaxing the contracted focus-adjustment muscles around the eyeball, such as the ciliary and extraocular muscles, improvement of the pseudo-myopia is expected. This understanding has led to the accommodation training in which the visual target is given by stereoscopic video clips. In this study, we verify short-term effects of the apparatus on eyesight of visual inspection workers (22 females) suffering from eye fatigue and 12 middle-aged persons. In the Measurement 1, the workers were trained in 3 days. Moreover, the middle-aged were investigated on several trials of the eyesight recovering apparatus in the Measurement 2. As a result, the visual acuity was statistically improved by continuous accommodation training which will promote a ciliary muscle-stretching effect.

Effect of display size on body sway in seated posture while viewing an hour-long stereoscopic film

Viewing stereoscopic films may have adverse effects, such as asthenopia and visually induced motion sickness (VIMS). The phenomenon of VIMS is not fully understood, so the aim of this study is to evaluate the effect of viewing a long stereoscopic film on the human body. We conducted stabilometric analysis on subjects in the Romberg posture, carried out flicker tests, and provided subjective questionnaires to detect fatigue and eye strain every 20 min. Symptoms of VIMS were detected during exposure to an hour-long stereoscopic film. The display size and the engagement were analyzed for their affect on the total locus length and the sway area, respectively. The severity of the motion sickness induced by viewing the 3D film was measured by stabilometry, and the analogous sway was not observed in participants after viewing the 2D film in this study. Based on these results, guidelines can be developed to ensure safety while viewing stereoscopic movies.

Effects of Two-Minute Stereoscopic Viewing on Human Balance Function

Recently, with the rapid progress in image processing and three-dimensional (3D) technologies, stereoscopic images are not only available on television but also in theaters, on game machines, and elsewhere. In contrast to two-dimensional (2D) films that project flat images, stereoscopic films elicit the feeling of being at a live performance. However, asthenopia and visually-induced motion sickness (VIMS) can result from the exposure to these films. Even though various hypotheses exist, the pathogenesis of VIMS is still unclear. There is not enough knowledge on the effects of stereoscopic images on the living body, and the accumulation of basic research is thus important. The aim of this paper is to accumulate information relevant to VIMS and to examine whether the exposure to 3D video clips affects the human equilibrium functions. We evaluated body sway by conducting stabilometry studies. As a result, we verified that 3D viewing effects on our equilibrium function depends on exposure time.

A Study on Within-Subject Factors for Visually Induced Motion Sickness by Using 8K Display

Visually induced self-motion perception (vection) is one of the phenomena related to human vision. It often emerges as a precursory symptom of motion sickness while viewing moving images. Employing a large number of subjects in a wide range of age groups and using a large-scale 8 K display, we investigated within-subject factors which can influence a sense of vection. We report some results of statistical analyses of vection-induced body sway which occurred when the subjects viewed rotating images on the display. Then we find that our fundamental study may provide useful information in order to set safety guidelines for large-scale ultra-high-definition displays such as 4K and 8K which are becoming popular in public use.

Limits of Cognition with Visual Parallax of Stereoscopic Images

OBJECTIVES Recent advances in three-dimensional (3D) display technology have contributed significantly to society, particularly in the increasing use of stereoscopic characters. For example, 3D text information is utilized in digital signage. However, research on 3D characters is limited and discussion on the safety and comfort of 3D technology is lacking. According to the 3D Consortium Safety Guidelines in Japan, a comfortable visual parallax with 3D images is less than ±1.0°. However, 3D text must be shown in front of its associated content in order for it to be displayed simultaneously with that content. METHODS We carried out an experiments to verify the permissive limits of cognition in subjects regarding the parallax of 3D images. In the experiment, 94 subjects aged 18 to 81 viewed a 3D flat Maltess cross image having no depth and projected outward from a screen at a large parallax of 1.0° to 6.0°. RESULTS Eighty-six percent of the subjects recognized the 3D flat image even when it protruded at a 2.0° parallax. These subjects viewed the image comfortably and without visual problems. CONCLUSIONS This study concludes that people can cognitively recognize a 3D telop at a 2.0° parallax without feeling fatigued.

Association between the Level of Blurring and Depth of Field in Watching Stereoscopic Images

Objective: The general explanation for visual fatigue with stereoscopic technology is that a mismatch of accommodation and convergence occurs during stereoscopic vision. Our previous studies measured lens accommodation and convergence simultaneously while subjects viewed stereoscopic video clips, and we found no discrepancy in young subjects. Since lens accommodation adjusts to the position of the virtual stereoscopic image, then the focus is not adjusted to the display surface, but to the virtual position. The question is whether or not a stereoscopic image might be blurred. We know that blurring is related to the changes in the depth of field which in turn is related to pupil diameter. We manipulated the luminance of displays and the environmental illuminance to affect the subjects’ pupil diameter to evaluate the level of blurring as subjects looked a visual acuity chart. The subjects were then asked to look at the same chart with various convex lenses to check if they could see a blurred image. We repeated this with a dimmed cover over the convex lens to measure the effects of darker conditions.

Evaluation of Body Sway in a Seated Posture after Alcohol Ingestion with an Aim to Evaluate Motion Sickness Caused by Three-Dimensional Images

A few studies have evaluated swaying motion of the body in the seated posture; however, these studies did not evaluate motion sickness caused by watching movies, traveling, etc. This study aimed to analyze stabilograms recorded while the individuals were seated. Stabilometry was performed on 7 healthy male subjects (age, 21–22 years) in the seated position 5 min before, and at 5-min intervals from 5 to 60 min after alcohol load. Alcohol caused a decrease in the cerebellar equilibrium function that controls the vestibulospinal reflex. We adjusted the degree of simulative effect on the human equilibrium function. The stabilograms of the test subjects were analyzed according to the area of sway, total locus length, and total locus length per unit area. We found that significant alcohol-induced changes in the sway values in the seated posture were similar to those in the upright posture.