Allison, Robert S

Tong, Jonathan

Wilcox, Laurie M

English

Purdue E-Pubs

                                                                                                                                                                                                                                                                                                                                                                                          		                                                                                     Modeling the impacts of inter-display and inter-lens separationon perceived slant in Virtual Reality Head-mounted displaysJonathan Tong Robert S Allison Laurie M WilcoxYork University York University York UniversityProjective geometry predicts that a mismatch between user interpupillary-distance (IPD) and the inter-axial separation of stereo cameras used to render imagery in VR will result indistortions of perceived scale. A potentially important, but often overlooked, consequence of amismatch between user IPD and VR lens separation is the impact on binocular convergence.Here we describe a geometric model that incorporates shifts in binocular convergence due tothe prismatic effect of decentered lenses, as well as the offset of dual displays relative to theeyes, and predicts biases in perceived slant. The model predicts that when the inter-lens andinter-display separation is less than an observer’s IPD, perceived slant will be biased towardsfrontoparallel. Conversely when the inter-lens and inter-display separation is greater than anobserver’s IPD, perceived slant will be increased. These predictions were tested andconfirmed in a VR headset with adjustable inter-lens and display separation (both coupled). Inthe experiment, observers completed a fold adjustment task in which they adjusted the anglebetween two intersecting, textured surfaces until they appeared to be perpendicular to oneanother. The task was performed at three randomly interleaved viewing distances,monocularly and binocularly. In separate blocks, the inter-lens and display separation waseither matched to the observer’s IPD (baseline condition) or set to the minimum or maximumallowed by the headset (IPD-mismatch conditions).  When the inter-lens and displayseparation was less than the observers’ IPD they underestimated surface slant relative tobaseline, and the reverse pattern was seen when the inter-lens and display separation wasgreater than their IPD. Overall, the geometric model tended to overestimate the effect of IPD-mismatch on perceived slant, especially at the farther viewing distances. We extended themodel to incorporate the relative weighting of monocular and binocular cues, resulting in anoverall improvement in the model fits. Our model provides researchers and VR-systems-designers a means of predicting depth perception when the optics of head-mounted displaysmay not be aligned with users’ eyes.Lens misaligned with eye o f-o IPDobs - IPDlens 2 focal point f (f-o)/f = / (IPDobs - IPDlens)/2 lens display Fig. 1: When the lens and display are misaligned with the Fig. 2: The adjusted angle in IPD-mismatch conditions relative to baseline (baselineeye, the vergence angle of each eye changes to – mismatch), plotted as a function of the difference between observer and headsetcompensate for the lateral shift, Δ, between the display IPD, for three tested viewing distancnce. Solid points are individual observer datacenter (equivalent to optical axis) and where the refracted points; the blue line is the linear regression best-fit, the original (binocular only)line of sight, due to the prismatic effect, intersects the model predictions are shown in red and the cue-combination extended modeldisplay. The principle of similar triangles can be used to predictions are shown in magenta. solve for Δ, given the expression on the right.

Modeling the impacts of inter-display and inter-lens separation on perceived slant in Virtual Reality Head-mounted displays

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1187&context=modvis

Modeling the impacts of inter-display and inter-lens separation on perceived slant in Virtual Reality Head-mounted displays

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