The relationship between CA/C ratio and individual differences in dynamic accommodative responses while viewing stereoscopic images

The oculomotor synergy as expressed by the CA/C and AC/A ratios was investigated to examine its influence on our previous observation that whereas convergence responses to stereoscopic images are generally stable, some individuals exhibit significant accommodative overshoot. Using a modified video refraction unit while viewing a stereoscopic LCD, accommodative and convergence responses to balanced and unbalanced vergence and focal stimuli (BVFS and UBVFS) were measured. Accommodative overshoot of at least 0.3 D was found in 3 out of 8 subjects for UBVFS. The accommodative response differential (RD) was taken to be the difference between the initial response and the subsequent mean static steady-state response. Without overshoot, RD was quantified by finding the initial response component. A mean RD of 0.11 +/- 0.27 D was found for the 1.0 D step UBVFS condition. The mean RD for the BVFS was 0.00 +/- 0.17 D. There was a significant positive correlation between CA/C ratio and RD (r = +0.75, n = 8, p <0.05) for only UBVFS. We propose that inter-subject variation in RD is influenced by the CA/C ratio as follows: an initial convergence response, induced by disparity of the image, generates convergence-driven accommodation commensurate with the CA/C ratio; the associated transient defocus subsequently decays to a balanced position between defocus-induced and convergence-induced accommodations

Dynamic measurement of accommodative responses while viewing stereoscopic images

Using video refraction accommodative and convergence dynamic responses were measured to stepped changes in convergence stimuli with unchanged accommodative stimuli (conflicting stereoscopic image) and compared with responses to non-conflicting target stimuli. Three targets were used that varied in their spatial frequency components. An accommodative transient overshoot was evident in four out of seven subjects for only conflicting stimuli. One showed accommodative and convergence oscillation probably due to difficulty in fusing the stereoscopic target when it had a higher spatial component, however, this oscillation diminished when the target was spatial low-pass filtered. We hypothesise that transient responses to step stimuli is initiated by convergence-driven accommodation and subsequently followed by slower fine-control of accommodation modulated by the amount of blur. Inter-subject differences in convergence-driven accommodation may also be a factor to consider. For stereoscopic stimuli, it is proposed that the increase in blur immediately after the onset of the accommodative response inhibits cessation of the response

視覚系の調節機構に関する研究-静的および準静的特性の解析-

制度:新 ; 文部省報告番号:甲683号 ; 学位の種類:工学博士 ; 授与年月日;1988-10-13 ; 早大学位記番号 : 新1453 ; 理工学図書館請求番号 : 1248早稲田大

Human Factors for Stereoscopic Images

Human factors related to stereoscopic motion images, such as visual stress, are introduced. Following a survey of studies on accommodation and convergence, difficulties in fusing two images, fatigue possibly due to a discrepancy between accommodative and convergence stimuli are introduced. Changes in oculomotor function after viewing stereoscopic images, and irreversible changes in oculomotor functions are also discussed. 1

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

Visual fatigue caused by viewing stereoscopic motion images: Background, theories, and observations

The background, theories, and observations on visual stress possibly caused by viewing stereoscopic motion images are reviewed. Visual fatigue caused by stereoscopic images is a safety issue. Fatigue is possible caused by the discrepancy between accommodative and convergence stimuli that are included in the image. Studies on accommodation and convergence are surveyed and an explanation regarding the characteristics of these functions is offered. Studies in the literature on changes in oculomotor function after viewing stereoscopic images, including changes in pupillary responses, are discussed. Evaluation of visual fatigue, particularly in relation to different methods of viewing stereoscopic displays is described

The Effect of S and Mn on the High-temperature Oxidation and Scale Spallation Behavior of Low-carbon Steels

Early-stage oxidation behavior in air of low-carbon steels with and without S and Mn additions was investigated in terms of oxidation kinetics and scale spallation in a temperature range of 900 to 1150°C. S and Mn did not appear to affect the growth rate of oxide scales within the given oxidation time, ~30 min, however it was found that S significantly enhanced oxide scale spallation. Scale spallation occurred only on the S doped steels oxidized at temperatures more than 1000°C when the thickness of oxide scale exceeded about 120 μm. This scale spallation was confirmed to occur during cooling after the given oxidation time. GD-OES analysis revealed that a significant amount of S enrichment occurred at the oxide/steel interface, which was around 1 mass% on 100 ppm S steel after 120 s of oxidation at 1150°C. Such sulfur enrichment was speculated to be due to accumulation of rejected S from surface recession during the high-temperature oxidation. Observation of the steel surface after complete removal of the oxide scale by quenching the steels into liquid nitrogen clearly indicates the formation of eutectic Fe–FeS structure at scale/steel interface, resulting from a liquid phase formation above 1000°C. Formation of sulfide, and therefore a liquid phase at higher temperature, greatly affected oxide scale spallation