Binocular Head-mounted Display Research Articles

Controlling readability of head-fixed large field-of-view displays

Background. The information displayed on a Head Mounted Display (HMD) can only be read by making eye movements, since head movements have no effect on the ocular image position. Aniseikonia (a common visual deficit) is expected to cause eye strain and limit the readability of large FoV binocular HMDs. As the FoV increases, the screen layout needs to optimize overall display readability by preventing clutter while taking common optometric conditions into account. Methods. We measured the ability to quickly determine the orientation of a target ⊤ (⊤ vs ⊥) surrounded by 4 randomly oriented (up, down, left, right) flanker T’s as a function of target-flanker spacing and eccentricity, in conditions where the target had either the same or opposite opposite luminance polarity as the flankers. All 12 subjects scored normal on relevant optometric tests (stereopsis, visual acuity, Awaya aniseikonia test, phoria). An aniseikonic lens placed in front of one eye optically enlarged the image by 2½%, simulating a common optometric condition. The additional delay caused by the presence of the four flankers is adopted as the ‘Crowding component’ of the reaction time. Results. Compared to the Same polarity condition, Opposite polarity reduced the Crowding time by a factor of 2.3 (p< 0.001). The Crowding times can be described as an extension of Fitts’ law. Unexpectedly, the mild aniseikonia condition doubled the Crowding time (p< 0.001) and caused the highest level of eye strain (p< 0.001). Conclusion. For all eccentricities and target-flanker spacings, the Crowding time more than halved in the opposite polarity condition, while it doubled due to the addition of just 2½% aniseikonia. Practical implications. Even users with mild aniseikonia are likely to experience problems while reading a large FOV HMD. ‘Polarity decluttering’ can significantly enhance symbology legibility.

Benefits of matching accommodative demands to vergence demands in a binocular head-mounted display

Current head-mounted displays HMDs provide only a fixed lens focus. Viewers have to decouple their accommodation and vergence responses when viewing stereoscopic images presented on an HMD. This st...

Benefits of Matching Accommodative Demands to Vergence Demands in a Binocular Head-Mounted Display: A Study on Stereo Fusion Times

Current head-mounted displays (HMDs) provide only a fixed lens focus. Viewers have to decouple their accommodation and vergence responses when viewing stereoscopic images presented on an HMD. This study investigates the time taken to fuse a pair of stereoscopic images displayed on an HMD when the accommodative demand is matched to the vergence demand. Four testing conditions exhausting the factorial combinations of accommodative demands (2.5 D and 0.5 D) and vergence demands (2.5 MA and 0.5 MA) were investigated. The results indicate that viewers take a significantly shorter amount of time to fuse a pair of stereoscopic images (i.e., fusion time) when the accommodative demand and the stereoscopic depth cues match. Further analysis suggests that an unnatural demand for the eyes to verge toward stereoscopic images whose stereo depth is farther than the accommodative demand is associated with significantly longer fusion time. This study evaluates the potential benefits of using a dynamically adjustable lens focus in future designs of HMDs.

Gait Deviations Induced by Visual Motion Stimulation in Roll Depend on Head Orientation

Locomotion control uses proprioceptive, visual, and vestibular signals. Previously, we analyzed the visual contribution with visual motion stimulation in roll while participants kept their heads in a normal upright orientation. In this study we applied the same visual disturbance in a head-upright and a nose-down condition. Random dot patterns were constantly rotated in roll at +/-15 degrees/sec on a computer-driven binocular head-mounted display, while the participants walked a distance of 6 m. The stimulation effect was more pronounced in the nose-down condition. These results are similar to the results of previous galvanic vestibular stimulation (GVS) studies, suggesting that in terms of the direction of action visual motion stimulation in the roll plane is similar to GVS.

Gait deviations induced by visual stimulation in roll

Locomotion control uses proprioceptive, visual, and vestibular signals. The vestibular contribution has been analyzed previously with galvanic vestibular stimulation (GVS), which constitutes mainly a virtual head-fixed rotation in the roll plane that causes polarity-specific deviations of gait. In this study we examined whether a visual disturbance has similar effects on gait when it acts in the same direction as GVS, i.e., when roll vection is induced by head-fixed visual roll motion stimulation. Random dot patterns were constantly rotated in roll at +/-15 degrees /s on a computer-driven binocular head-mounted display that was worn by eight healthy participants. Their gait trajectories were tracked while they walked a distance of 6 m. A stimulation effect was observed only for the first three to four steps, but not for the whole walking distance. These results are similar to the results of previous GVS studies, suggesting that in terms of the direction of action visual motion stimulations in the roll plane are similar to GVS. Both kinds of stimulation cause only initial balance responses in the roll plane but do not contribute to the steering of gait in the yaw plane.

Binocular vision in a bi-ocular world: new-generation head-mounted displays avoid causing visual deficit

Our previous research highlighted adverse visual effects after wearing a binocular head-mounted display (HMD) for a 10 min stereoscopic visualization task. We have since proposed a theoretical, explanation based on the conflict between the depth. Such cues presented by image disparity and image focal depth. Such conflict, however, is not evident in all HMD configurations, and we replicated our early trials using a new-generation bi-ocular HMD produced by Virtuality Entertainment Ltd. Using similar, conventional optometric procedures with 50 participants, we observed no problems in the use of this display for immersion periods of to 30 min. This study demonstrates that effective HMDs can be produced through careful design and precision engineering. It also suggests a difference between the presentation of binocular and bi-ocular images and the requirements that they place on the visual system. Factors to consider in the future development of binocular displays are discussed.