Vertical gaze direction and the resting posture of the eyes

Projection Screen with Wide-FOV and Motion Parallax Display for Teleoperation of Construction Machinery

The teleoperation of construction machinery has been introduced to mines and disaster sites. However, the work efficiency of teleoperations is lower than that of onboard operations owing to limitations in the viewing angle and insufficient depth information. To solve these problems and realize effective teleoperations, the Komatsu MIRAI Construction Equipment Cooperative Research Center is developing the next-generation teleoperation cockpit. In this study, we develop a display for teleoperations with a wide field-of-view, a portable projection screen, and a system that reproduces motion parallax, which is suitable for depth perception in the operating range of construction machinery.

A Geometric Theory Integrating Human Binocular Vision With Eye Movement

A theory of the binocular system with asymmetric eyes (AEs) is developed in the framework of bicentric perspective projections. The AE accounts for the eyeball's global asymmetry produced by the foveal displacement from the posterior pole, the main source of the eye's optical aberrations, and the crystalline lens' tilt countering some of these aberrations. In this theory, the horopter curves, which specify retinal correspondence of binocular single vision, are conic sections resembling empirical horopters. This advances the classic model of empirical horopters as conic sections introduced in an ad hoc way by Ogle in 1932. In contrast to Ogle's theory, here, anatomically supported horopteric conics vary with the AEs' position in the visual plane of bifoveal fixations and their transformations are visualized in a computer simulation. Integrating horopteric conics with eye movements can help design algorithms for maintaining a stable perceptual world from visual information captured by a mobile robot's camera head. Further, this paper proposes a neurophysiologically meaningful definition for the eyes' primary position, a concept which has remained elusive despite its theoretical importance to oculomotor research. Finally, because the horopteric conic's shape is dependent on the AE's parameters, this theory allows for changes in retinal correspondence, which is usually considered preformed and stable.

Training Performance of Laparoscopic Surgery in Two- and Three-Dimensional Displays

INTRODUCTION

This research investigated differences in the effects of a state-of-art stereoscopic 3-dimensional (3D) display and a traditional 2-dimensional (2D) display in simulated laparoscopic surgery over a longer duration than in previous publications and studied the learning effects of the 2 display systems on novices.

METHODS

A randomized experiment with 2 factors, image dimensions and image sequence, was conducted to investigate differences in the mean movement time, the mean error frequency, NASA-TLX cognitive workload, and visual fatigue in pegboard and circle-tracing tasks.

RESULTS

The stereoscopic 3D display had advantages in mean movement time ( P < .001 and P = .002) and mean error frequency ( P = .010 and P = .008) in both the tasks. There were no significant differences in the objective visual fatigue ( P = .729 and P = .422) and in the NASA-TLX ( P = .605 and P = .937) cognitive workload between the 3D and the 2D displays on both the tasks. For the learning effect, participants who used the stereoscopic 3D display first had shorter mean movement time in the 2D display environment on both the pegboard ( P = .011) and the circle-tracing ( P = .017) tasks.

CONCLUSIONS

The results of this research suggest that a stereoscopic system would not result in higher objective visual fatigue and cognitive workload than a 2D system, and it might reduce the performance time and increase the precision of surgical operations. In addition, learning efficiency of the stereoscopic system on the novices in this study demonstrated its value for training and education in laparoscopic surgery.

Effects of VDT Viewing Angle on User Biomechanics, Comfort, and Preference

A study was conducted to characterize effects of computer monitor viewing angle on operators. The study was conducted in two phases: controlled laboratory experiment followed by field verification. Lab results are discussed here. Three viewing angles were studied: 0, -17.5, and -35 deg to center of screen. Effects of monitor size and keyboard familiarity were also investigated. Muscle activity, body posture, visual acuity, performance, discomfort, and preference data were collected. In general, muscle activity was greater at -35 deg than at 0 deg; and greater for a smaller monitor than a larger one. Only head postures were affected by viewing angle. The eye-ear line was angled higher for touch typists. Mousing performance slowed slightly at 0 deg. Subjects preferred the -17.5 deg angle most and the -35 deg angle least. Results suggest there could be benefits to using a larger monitor with viewing angle between -17.5 to 0 deg for screen-intensive work.

Hitting the Target: Relatively Easy, Yet Absolutely Difficult

It is generally agreed that absolute-direction judgments require information about eye position, whereas relative-direction judgments do not. The source of this eye-position information, particularly during monocular viewing, is a matter of debate. It may be either binocular eye position, or the position of the viewing-eye only, that is crucial. Using more ecologically valid stimulus situations than the traditional LED in the dark, we performed two experiments. In experiment 1, observers threw darts at targets that were fixated either monocularly or binocularly. In experiment 2, observers aimed a laser gun at targets while fixating either the rear or the front gunsight monocularly, or the target either monocularly or binocularly. We measured the accuracy and precision of the observers' absolute- and relative-direction judgments. We found that (a) relative-direction judgments were precise and independent of phoria, and (b) monocular absolute-direction judgments were inaccurate, and the magnitude of the inaccuracy was predictable from the magnitude of phoria. These results confirm that relative-direction judgments do not require information about eye position. Moreover, they show that binocular eye-position information is crucial when judging the absolute direction of both monocular and binocular targets.

Functional specialization in the lower and upper visual fields in humans: Its ecological origins and neurophysiological implications

Functional specialization in the lower and upper visual fields in humans is analyzed in relation to the origins of the primate visual system. Processing differences between the vertical hemifields are related to the distinction between near (peripersonal) and far (extrapersonal) space, which are biased toward the lower and upper visual fields, respectively. Nonlinear/global processing is required in the lower visual field in order to pergeive the optically degraded and diplopic images in near vision, whereas objects in far vision are searched for and recognized primarily using linear/local perceptual mechanisms. The functional differences between near and far visual space are correlated with their disproportionate representations in the dorsal and ventral divisions of visual association cortex, respectively, and in the magnocellular and parvocellular pathways that project to them. Advances in far visual capabilities and forelimb manipulatory skills may have led to a significant enhancement of these functional specializations.

The role of the extrapersonal brain systems in religious activity

The neuropsychology of religious activity in normal and selected clinical populations is reviewed. Religious activity includes beliefs, experiences, and practice. Neuropsychological and functional imaging findings, many of which have derived from studies of experienced meditators, point to a ventral cortical axis for religious behavior, involving primarily the ventromedial temporal and frontal regions. Neuropharmacological studies generally point to dopaminergic activation as the leading neurochemical feature associated with religious activity. The ventral dopaminergic pathways involved in religious behavior most closely align with the action-extrapersonal system in the model of 3-D perceptual-motor interactions proposed by . These pathways are biased toward distant (especially upper) space and also mediate related extrapersonally dominated brain functions such as dreaming and hallucinations. Hyperreligiosity is a major feature of mania, obsessive-compulsive disorder, schizophrenia, temporal-lobe epilepsy and related disorders, in which the ventromedial dopaminergic systems are highly activated and exaggerated attentional or goal-directed behavior toward extrapersonal space occurs. The evolution of religion is linked to an expansion of dopaminergic systems in humans, brought about by changes in diet and other physiological influences.

Gaze Affects Pointing Toward Remembered Visual Targets After a Self-Initiated Step

We have investigated pointing movements toward remembered targets after an intervening self-generated body movement. We tested to what extent visual information about the environment or finger position is used in updating target position relative to the body after a step and whether gaze plays a role in the accuracy of the pointing movement. Subjects were tested in three visual conditions: complete darkness (DARK), complete darkness with visual feedback of the finger (FINGER), and with vision of a well-defined environment and with feedback of the finger (FRAME). Pointing accuracy was rather poor in the FINGER and DARK conditions, which did not provide vision of the environment. Constant pointing errors were mainly in the direction of the step and ranged from about 10 to 20 cm. Differences between binocular fixation and target position were often related to the step size and direction. At the beginning of the trial, when the target was visible, fixation was on target. After target extinction, fixation moved away from the target relative to the subject. The variability in the pointing positions appeared to be related to the variable errors in fixation, and the co-variance increases during the delay period after the step, reaching a highly significant value at the time of pointing. The significant co-variance between fixation position and pointing is not the result of a mutual dependence on the step, since we corrected for any direct contributions of the step in both signals. We conclude that the co-variance between fixation and pointing position reflects 1) a common command signal for gaze and arm movements and 2) an effect of fixation on pointing accuracy at the time of pointing.

Interaction between gaze and pointing toward remembered visual targets

We examined the role of gaze in a task where subjects had to reproduce the position of a remembered visual target with the tip of the index finger, referred to as pointing. Subjects were tested in 3 visual feedback conditions: complete darkness (dark), complete darkness with visual feedback of the finger position (finger), and with vision of a well-defined environment and feedback of the finger position (frame). Pointing accuracy increases with feedback about the finger or visual environment. In the finger and frame conditions, the 95% confidence regions of the variable errors have an ellipsoidal distribution with the main axis oriented toward the subjects' head. During the 1-s period when the target is visible, gaze is almost on target. However, gaze drifts away from the target relative to the subject in the delay period after target disappearance. In the finger and frame conditions, gaze returns toward the remembered target during pointing. In all 3 feedback conditions, the correlations between the variable errors of gaze and pointing position increase during the delay period, reaching highly significant values at the time of pointing. Our results demonstrate that gaze affects the accuracy of pointing. We conclude that the covariance between gaze and pointing position reflects a common drive for gaze and arm movements and an effect of gaze on pointing accuracy at the time of pointing. Previous studies interpreted the orientation of variable errors as indicative for a frame of reference used for pointing. Our results suggest that the orientation of the error ellipses toward the head is at least partly the result of gaze drift in the delay period.

The proximity-fixation-disparity curve and the preferred viewing distance at a visual display as an indicator of near vision fatigue

PURPOSE

This laboratory study investigates the relation between measures of fixation disparity (FD) (and other optometric measures) and near vision fatigue at a computer workstation.

METHODS

Young adult subjects with normal binocular vision performed three blocks of a visual task of 30 min each. In Block A, the viewing distance was 100 cm, as a reference without near vision. In Block B, the viewing distance of 50 cm induced a defined near vision load. In Block C, subjects were free to choose a comfortable viewing distance. This preferred viewing distance was used as an indicator of near vision fatigue because subjects adopting longer viewing distances in Block C had more near vision fatigue at 50 cm in Block B.

RESULTS

Subjects with preferred viewing distances longer than average (63 cm) had steeper slopes of FD as a function of viewing distance (100-30 cm), as shown by discriminant analyses.

CONCLUSIONS

Thus, this steep proximity-FD curve indicates a weak disparity vergence system that may cause near vision fatigue. This may explain why some young adults prefer longer viewing distances at the computer workstation.

Fixation disparity: binocular vergence accuracy for a visual display at different positions relative to the eyes

Some observers do not fixate accurately at the point of regard: Their vergence angle (between the visual axes of the two eyes) may correspond to points slightly nearer or farther away. This vergence error, or fixation disparity, was measured with nonius (vernier) lines at six positions of a visual display relative to the eyes. At viewing distances of 40, 60, and 100 cm, the display was located either at eye level or at a downward inclination of gaze direction of -25 degrees relative to horizontal. Viewing conditions resembled typical office work. Lowering the screen induced a near shift in mean vergence response of 0.6 min arc, irrespective of viewing distance; the closer the screen, the more distant was the vergence response relative to the target (by 2.5 min arc on average). The slope of this proximity-fixation-disparity curve is an individual parameter of the vergence system. Actual or potential applications of this research include recommendations for the comfortable viewing distance of visual displays.

Effects of computer monitor viewing angle and related factors on strain, performance, and preference outcomes

A model of visual and musculoskeletal strain associated with computer monitor placement was developed. The main premise of which is that monitor placement decisions must take into consideration development of both visual and musculoskeletal strains. Certain factors in the model that were thought to affect one or both types of strain. or that were considered important to rule out for effect, were tested in a lab setting. These factors were viewing angle (eye level, midlevel, low level), monitor size (14 in., 19 in.), keyboard familiarity (touch typist, nontouch typist), and task (reading, mousing, typing). Outcomes included indicators of visual and musculoskeletal strain, preference, and performance. Muscle activity was generally greater for the low viewing angle, for the standard monitor (14 in.), and for non-touch typists. Participants preferred the midlevel placement. Task performance was slightly diminished with eye-level placement. Results are interpreted in relation to the model and to several hypotheses that were formed to focus the inquiry. Actual or potential applications of this research include monitor placement decisions in the design or modification of computer workstations.

A procedure to determine the individually comfortable position of visual displays relative to the eyes

In an intervention phase, 38 operators used four different imposed screen positions (near versus distant, high versus low) for a full working day to experience the advantages and disadvantages. Screens at about 66 cm induced more reported strain than screens at about 98 cm. When operators later freely selected their individually most comfortable screen position, individually different changes due to the intervention were observed: some subjects changed to shorter, others to longer viewing distances, some operators adjusted the screen lower, others higher. These effects were confirmed in repeated tests. Thus, trying out different screen positions appears useful for arranging the VDU workstation to the individually most comfortable screen location relative to the eyes.

Preferred position of visual displays relative to the eyes: a field study of visual strain and individual differences

At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and -16 degrees downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.

Gaze angle: a possible mechanism of visual stress in virtual reality headsets

It is known that some Virtual Reality (VR) head-mounted displays (HMDs) can cause temporary deficits in binocular vision. On the other hand, the precise mechanism by which visual stress occurs is unclear. This paper is concerned with a potential source of visual stress that has not been previously considered with regard to VR systems: inappropriate vertical gaze angle. As vertical gaze angle is raised or lowered the 'effort' required of the binocular system also changes. The extent to which changes in vertical gaze angle alter the demands placed upon the vergence eye movement system was explored. The results suggested that visual stress may depend, in part, on vertical gaze angle. The proximity of the display screens within an HMD means that a VR headset should be in the correct vertical location for any individual user. This factor may explain some previous empirical results and has important implications for headset design. Fortuitously, a reasonably simple solution exists.

Postural load during VDU work: a comparison between various work postures

The aim of this study was to compare the postural load during VDU work in the following work postures: (1) Supporting and not supporting the forearms on the table top, (2) Sitting and standing positions, and (3) Sightline to the centre of the screen at an angle of 15 degrees and 30 degrees below the horizontal. The muscle load from the upper part of musculus trapezius and from the lumbar part of musculus erector spinae (L3 level) was measured by electromyography (EMG). Postural angles of head, upper arm and back were measured by inclinometers. The load on m. trapezius when using the keyboard was significantly less in sitting with supported forearms compared to sitting and standing without forearm support. Further, the time and number of periods when the trapezius load was below 1% MVC was significantly greater with support versus no support. The load on the right erector spinae lumbalis was also significantly less and the time when the load was below 1% MVC was significantly longer in a sitting work position with support versus standing without support. In addition, when using a mouse supporting the forearms reduced the static trapezius load in sitting. The results from this study document clearly the importance of giving the operator the possibility of supporting the forearms on the table top.

Preferred viewing distances for handheld and structurally fixed displays

This research was conducted to define viewing distance characteristics of individuals engaged in ordinary reading tasks. Specific attention was directed to assessing the potential relationship between observed distance and individual resting point accommodation. Consistent, statistically significant differences were observed across variable handheld and structurally-fixed hardcopy display configuration conditions. Relationships between observed viewing distance and resting point accommodation were not apparent. These findings suggest that simple eye-to-display viewing distance is fundamentally different for handheld text presentations and for the same text presented in a configuration similar to that of a video display terminal.

Convergence responses to monocularly viewed objects: implications for distance perception

In four experiments the role of dark vergence and the implied distance from the familiar-size and suggested-size cues to distance on the convergence response was investigated. A nonius-alignment technique was used to measure the convergence response in total darkness (dark vergence) and the fusion-free convergence response to monocularly viewed objects presented at a distance of 75 cm under otherwise reduced stimulus conditions. Observers also estimated the size and distance of the objects. The results indicated a significant association between individuals' dark-vergence distances and the convergence distances to the objects. Furthermore, the convergence response was influenced by the implied distance from the familiar-size cue but not by the implied distance from size suggestions. Both the familiar-size and the suggested-size cues influenced reports of distance. The implications of these findings for distance perception are discussed with particular reference to the familiar-size cue to distance.

Vergence can be controlled by audio feedback, and induces downward ocular deviation

We measured horizontal and vertical eye positions, using binocular search coils, in three humans. Subjects could maintain vergence by means of audio biofeedback. Feedback consisted of a pair of audio tones, one variable and one fixed at a reference frequency. The variable tone was controlled by instantaneous vergence and provided immediate feedback on the vergence state. The reference frequency, which they attempted to match, was set to correspond to a target distance of either 0.34 m or 0.14 m. Subjects could maintain vergence consistently, even while undergoing lateral motions at 0.5 Hz and 0.2 g peak acceleration in darkness. There was also a consistent tendency for the eyes to deviate downward during near vergence. The results may be useful in experiments in which one wishes to control vergence without providing a visual reference which might inhibit conjugate eye movements.

Moon illusion simulated in complete darkness: planetarium experiment reexamined

In 1962, Kaufman and Rock reported that the moon illusion did not occur in the darkness of a planetarium or in a completely dark room. The present study reexamined their findings. Two pairs of light points, separated by 3.5 degrees, were presented on the dome screen of a planetarium. Subjects compared the distance between the two light points presented in the horizontal direction with the distance between the two light points at the zenith. Three illumination conditions were used: The inside of the planetarium was completely dark, was lighted, or was projected with the silhouette of a city under a starry sky. The effect of eye elevation on the illusion was also examined. Contrary to Kaufman and Rock's results, a size discrepancy comparable to the moon illusion was obtained in the horizon-and-stars condition and even in the complete-darkness condition. Little or no illusion was obtained in the lighted-room condition. The results also showed that eye elevation affected the magnitude of the illusion.