Effects on visual functions during tasks of object handling in virtual environment with a head mounted display

Effects of Immersive Virtual Reality Headset Viewing on Young Children: Visuomotor Function, Postural Stability, and Motion Sickness

PURPOSE

To assess the safety of VR 3D headset (virtual reality 3-dimensional binocular-stereoscopic near-eye display) use in young children. Product safety warnings that accompany VR headsets ban their use in children under age 13 years.

DESIGN

Prospective, interventional, before-and-after study.

METHODS

Recordings were obtained in 50 children (29 boys) aged 4-10 years (mean 7.2 ± 1.8 years). Minimum binocular corrected distance visual acuity (CDVA) was 20/50 (logarithm of the minimum angle of resolution [logMAR] 0.4) and stereoacuity 800 seconds of an arc or better. A Sony PlayStation VR headset was worn for 2 sequential play sessions (of 30 minutes each) of a first-person 3D flying game (Eagle Flight) requiring head movement to control flight direction (pitch, yaw, and roll axes). Baseline testing preceded VR exposure, and each VR session was followed by post-VR testing of binocular CDVA, refractive error, binocular eye alignment (strabismus), stereoacuity, and postural stability (imbalance). Visually induced motion sickness was probed using the Simulator Sickness Questionnaire modified for pediatric use (Peds SSQ). Visual-vestibulo-ocular reflex (V-VOR) adaptation was also tested pre- vs post-trial in 5 of the children. Safety was gauged as a decline or change from baseline in any visuomotor measure.

RESULTS

Forty-six of 50 children (94%) completed both VR play sessions with no significant change from baseline in measures of binocular CDVA (P = .89), refractive error (P = .36), binocular eye alignment (P = .90), or stereoacuity (P = .45). Postural stability degraded an average 9% from baseline after 60 minutes of VR exposure (P = .06). Peds SSQ scores increased a mean 4.7%-comparing pretrial to post-trial-for each of 4 symptom categories: eye discomfort (P = .02), head/neck discomfort (P = .03), fatigue (P = .03), and motion sickness (P = .01). None of the children who finished both trial sessions (94%) asked to end the play, and the majority were disappointed when play was halted. V-VOR gain remained unaltered in the 5 children tested. Three children (6% of participants) discontinued the trial during the first 10 minutes of the first session of VR play, 2 girls (aged 5 and 6 years) and 1 boy (aged 7 years). The girls reported discomfort consistent with mild motion sickness; the boy said he was bored and the headset was uncomfortable. No child manifested aftereffects ("flashbacks") in the days following the VR exposure.

CONCLUSION

Young children tolerate fully immersive 3D virtual reality game play without noteworthy effects on visuomotor functions. VR play did not induce significant post-VR postural instability or maladaption of the vestibulo-ocular reflex. The prevalence of discomfort and aftereffects may be less than that reported for adults.

Head-Mounted Displays: Are They Practical for School-Age Children?

Head-mounted displays (HMDs) for people with low vision are video devices with user-controlled variable magnification and some degree of contrast enhancement. In this preliminary study of visually impaired students in a residential school, HMDs improved acuity and contrast sensitivity, prevented glare, and enhanced performance of near, intermediate, and distance tasks, including mobility. The study also showed that students enjoyed using the devices.

Differential effects of head-mounted displays on visual performance

Head-mounted displays (HMDs) virtually augment the visual world to aid visual task completion. Three types of HMDs were compared [look around (LA); optical see-through with organic light emitting diodes and virtual retinal display] to determine whether LA, leaving the observer functionally monocular, is inferior. Response times and error rates were determined for a combined visual search and Go-NoGo task. The costs of switching between displays were assessed separately. Finally, HMD effects on basic visual functions were quantified. Effects of HMDs on visual search and Go-NoGo task were small, but for LA display-switching costs for the Go-NoGo-task the effects were pronounced. Basic visual functions were most affected for LA (reduced visual acuity and visual field sensitivity, inaccurate vergence movements and absent stereo-vision). LA involved comparatively high switching costs for the Go-NoGo task, which might indicate reduced processing of external control cues. Reduced basic visual functions are a likely cause of this effect.

Target spatial frequency determines the response to conflicting defocus- and convergence-driven accommodative stimuli

Asthenopia, or visual fatigue, is a frequent complaint from observers of stereoscopic three-dimensional displays. It has been proposed that asthenopia is a consequence of anomalous oculomotor responses generated by conflict between accommodative and convergence stimuli. The hypothesis was examined by measuring accommodation and convergence continuously with a Shin-Nippon SRW5000 infrared autorefractor and a limbus tracking device. Subjects viewed a high contrast Maltese Cross target at three levels of Gaussian filter target blur under conditions of relatively low- and high-conflict between accommodation and convergence stimuli, the latter inducing the sensation of stereopsis. Under the low-conflict conditions accommodation was stable, but convergence-driven accommodation was dominant when the target was extremely blurred. Under the high-conflict conditions the role of convergence-driven accommodation increased systematically with the degree of target blur. It is proposed that defocus-driven accommodation becomes weak when the target comprises low spatial frequency components. Large accommodative overshoots to step stimuli that are not blurred or only mildly blurred were consistently observed and are attributed to the initial accommodative response being convergence-driven. Whereas the possibility that high-conflict conditions are a cause of asthenopia has been previously reported, this is the first evidence that they specifically affect accommodative responses while viewing stereoscopic displays.

The effects of direction and movement of attractors on users' behavior in virtual environments

Despite fast technological developments in virtual reality (VR), methodologies and guidelines for evaluating the design of virtual environments (VEs) are lacking. The theory of perceptual opportunities (POs) has previously been proposed as a basis of such a design methodology. This paper presents an empirical study investigating the effect of representation of POs on users' behavior in VEs. The effects of both direction and movement of attractor on choice of objects in a simple VE were studied. Results showed that vertical static attractors were chosen least frequently. Furthermore, there was an effect of direction for static attractors in favor of the take-off direction. Implications for VE design in the framework of POs are discussed.

Combined and interacting effects of hand and head movement delays on discrete manual performance in a virtual environment

Transmission delays occur when a virtual environment responds to the hand and head movements of an operator. The effects of hand and head-related delays on discrete manual performance was investigated experimentally and compared. Imposed hand and head-related pure delays equal to or greater than 110 ms and 220 ms, respectively, significantly increased hand Movement Time (MT). The effect of hand-related delays was greater than that of head-related delays of the same magnitude. A regression model describing the combined effects of both delays on MT is reported (R(2) = 0.95). Analyses of the interactions among delays, target width, and distances have shown the need to adopt the traditional classification of delays into (1) control delay, and (2) display delay. The use of this taxonomy and the regression analyses to describe and explain the effects of individual and combined effects of delays on discrete target-reaching task performance in virtual environments are discussed.

Effects of a target movement direction cue on head-tracking performance

A review of the literature has shown that most investigations of head-tracking performance have used symmetrically shaped targets. This paper identifies a problem in using circular targets to represent the movement of complex targets (i.e. targets giving directional cues). Two experiments investigated the effects of a target direction cue on head-tracking performance. In the first experiment, practice did not improve performance when tracking either with or without a 'look-ahead trace' showing all target positions 160 ms into the future. A second experiment utilized a 'look-ahead trace' showing target positions with eight different lead-times (0-560 ms). With lead-times of 160 ms or more, significant improvements in tracking performance and subjective difficulty ratings were obtained. Tracking responses were also significantly affected. The results suggest caution when performance data obtained with a symmetrical target are generalized to predict tracking performance with a real target giving cues to the direction of movement. The look-ahead trace offers a systematic means of bridging the gap between a symmetrical target and a real target having direction of movement cues.