Peter A. Howarth

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.

Potential hazards of viewing 3-D stereoscopic television, cinema and computer games: a review

Citation information: Howarth PA. Potential hazards of viewing 3‐D stereoscopic television and cinema: a review. Ophthalmic Physiol Opt 2011, 31, 111–122. doi: 10.1111/j.1475‐1313.2011.00822.x

The occurrence of virtual simulation sickness symptoms when an HMD was used as a personal viewing system

Abstract The effects of using a lightweight HMD as a personal viewing system were examined. When used in this manner, with head-tracking disabled, a sensory conflict which is novel for simulations arises: head movements are detected by the vestibular system but not by the visual system. To investigate the effects of this conflict, ratings of a number of symptoms were reported by 20 subjects before and after they used an HMD for one hour. The results were compared with ratings the same subjects made when viewing a VDU, where the task was the same but the conflict was absent. Of the two conditions, the former produced a significantly greater frequency of increase in the following symptoms: general discomfort, fatigue, headache, nausea, dizziness, stomach awareness, hot or burning eyes, double vision and general visual discomfort. The HMD results were also compared with those from a previous study in which the same headset was used, but configured for VR applications with head-tracking enabled. Surprisingly, given that update lag, cues for vection-induced motion, and accommodation/convergence conflict were all absent, an increase in some symptoms was more frequently reported for the personal viewing configuration.

The nauseogenicity of two methods of navigating within a virtual environment

This study compared the nauseogenicity of two different strategies for exploring virtual environments whilst wearing an immersive head-mounted display. In the first, the head was kept still and movement was achieved solely by manipulating a hand-control. In the second, the subject was free (and encouraged) to move his or her head when exploring the virtual world. Fourteen subjects completed both of the 20 min trials, three further subjects withdrew from the study after one trial. Subjects reported increases in adverse symptoms when using each strategy and, for the group as a whole, nausea increased steadily during each immersion period. However, significantly larger changes were reported when the head moved than when it was still, as predicted from sensory conflict theory.

Does the chromatic aberration of the eye vary with age

The longitudinal chromatic aberration of the eye has been reported to decline with age. Using three different methods, we have measured the aberration in a group of young subjects (27-33 years old) and a group of older subjects (48-72 years old). In two of the methods we used a Badal optometer, either with or without an achromatizing lens incorporated, to examine the effect of wavelength on refractive error. In the third method we used a vernier-alignment apparatus to assess chromatic dispersion directly. None of the results of the experiments performed revealed any difference in aberration between the groups. Furthermore, a linear regression of aberration against age showed no relationship between these variables. We conclude that, for human adults, the magnitude of chromatic aberration is independent of age.

Oculomotor changes within virtual environments

This paper discusses the oculomotor changes which might be expected to occur during immersion in a virtual environment whilst wearing a Head mounted display (HMD). To do so, it first examines the stimulus presented to the eyes, and then considers how this stimulus could affect the visual system. Theoretical analysis and empirical results from the use of three different HMDs point towards the same conclusion, that in this context a mismatch between the instrument inter-ocular distance (IOD) and the users inter-pupillary distance is of little concern, unlike the mismatch between the instrument IOD and the inter-screen distance.

Characteristics of habituation to motion in a virtual environment

Immersion in a virtual environment is known to produce symptoms similar to those of motion sickness. With repeated immersions, these symptoms are generally reduced in prevalence and severity. We aimed to quantify this habituation by immersing 70 people on ten occasions each. Ten participants were exposed every day, ten every 2 days, and so on up to every 7 days. The participants played a PC racing game, viewed through a head mounted display, for 20 min. They rated various motion sickness symptoms both before and after exposure, and rated their level of malaise at 1-min intervals during immersion. After completion of the ten trials, all sets of participants reported a marked reduction in the prevalence and severity of the symptoms. The habituation which occurred was of a similar nature in all of the participant groups regardless of exposure interval, indicating that the number of exposures is a more important factor than the time interval between them.

The association between visual discomfort and the use of visual display units

Abstract This paper reports the results of a two-year survey of the visual problems associated with the use of visual display units (VDUs). The survey examined both discomfort levels and visual function, and asked whether there were differences in these measures between subjects who used a VDU in the completion of their tasks and controls who did not. In total, 202 subjects were examined. The main study examined four groups of which two, Data Preparation and Word Processing (WP) used a VDU in the completion of their tasks, while the other two, General Clerical and Typing (TY), did not. Subjective measures of visual discomfort and objective measures of visual function were taken at both the beginning and end of the day. Two analyses were performed on the data; the first considered all four groups together, and the second directly compared the WP and TY groups—these two groups being considered well matched. The first analysis showed that statistically significant differences existed between the groups at th...

Frequency Characteristics of Visually Induced Motion Sickness

Objective: The aim of this study was to explore the frequency response of visually induced motion sickness (VIMS) for oscillating linear motion in the fore-and-aft axis. Background: Simulators, virtual environments, and commercially available video games that create an illusion of self-motion are often reported to induce the symptoms seen in response to true motion. Often this human response can be the limiting factor in the acceptability and usability of such systems. Whereas motion sickness in physically moving environments is known to peak at an oscillation frequency around 0.2 Hz, it has recently been suggested that VIMS peaks at around 0.06 Hz following the proposal that the summed response of the visual and vestibular self-motion systems is maximized at this frequency. Methods: We exposed 24 participants to random dot optical flow patterns simulating oscillating fore-and-aft motion within the frequency range of 0.025 to 1.6 Hz. Before and after each 20-min exposure, VIMS was assessed with the Simulator Sickness Questionnaire. Also, a standard motion sickness scale was used to rate symptoms at 1-min intervals during each trial. Results: VIMS peaked between 0.2 and 0.4 Hz with a reducing effect at lower and higher frequencies. Conclusion: The numerical prediction of the “crossover frequency” hypothesis, and the design guidance curve previously proposed, cannot be accepted when the symptoms are purely visually induced. Application: In conditions in which stationary observers are exposed to optical flow that simulates oscillating fore-and-aft motion, frequencies around 0.2 to 0.4 Hz should be avoided.

Repeated measures of horizontal heterophoria.

Purpose To assess repeatability, horizontal heterophoria measurements were taken from 31 subjects on five occasions, each between 1 and 4 weeks apart. Method Distance heterophoria was measured using a Maddox Rod, and near heterophoria was measured using a Maddox Wing. In addition, near measurements were repeated with a +3.00 D lens in front of each eye to place the targets at optical infinity. In each case, the standard deviation of the five values was taken as a metric of the test variability. Results On average, the variability of the Maddox Rod was half of the Maddox Wing, both with and without the lenses. Conclusion This consistency suggests that the difference reflects the test conditions rather than optical differences in the target position.