Virtual scale changes perception of distance and of one's own size

What it is

Drop virtual eye height to a child’s line of sight and the same corridor looks longer; the self feels shorter. Virtual scale — through eye height, rendered IPD, uniform scaling — rewrites distance and own size together. This is not a missing ruler in the scene, and not a ruler that will stick to the next cup. It is the current projection geometry recalibrating space and the body at once.

Compressed or stretched distance, and “I have become a child / a giant,” are two faces of one geometry.

Why it happens

Eye height is a primary ground-scale cue: by habit, the density of ground texture ahead and the height of the visual horizon say how tall I am and how far that wall is. Lower virtual eye height and the same ground is read as farther, the self as shorter; raise it and space flattens, the self like someone on stilts. A rendered IPD that disagrees with real IPD is parsed as “the world grew or shrank,” and distance goes with it. Uniformly scaling camera and world also changes the rate of motion parallax, so the visual result of a stride no longer matches the legs.

These are concurrent perceptual effects; they do not need minutes of adaptation. Before anyone walks over to check with their feet, verbal distance and “how tall I feel” already bias. A slice of the distance underestimation common in VR is this scale geometry — eye height, IPD, ground texture — not being calibrated to the real body.

Studying it

Use blind walking, verbal distance estimates, and “show with both hands how tall you are now” or an adjustable avatar height, under different virtual eye heights, rendered IPDs, and uniform scales. Baseline is 1:1 calibrated to real stature and IPD. Watch whether distance error and own-height error move in the same direction — same direction means one virtual ruler is moving, not two independent illusions.

Report ground texture, horizon, and whether the feet are visible, or an eye-height manipulation will be contaminated by “no ground.” A seated session still rendered at standing eye height is itself a scale condition.

Where it stops holding

With no visible ground and no horizon — space, void — the eye-height cue is absent and adjusting it will not rewrite distance by this rule. People who are really walking will calibrate distance with step count and the weight of visual scale drops. An accurate self-avatar and hands pin own-size judgments to the avatar, which then follow eye height less; distance may still bias. Under optical see-through, real ground fights virtual eye height and the effect is unstable. A few centimetres of eye-height error and rewriting an adult to a child’s line of sight are not the same magnitude; only the latter reliably shifts both distance and stature sense.

Applying it

• Calibrate virtual eye height and IPD to real stature and interpupillary distance. Seated use seated height; do not put standing eye height on a chair.
• When a change of scale sense is intended, accept that distance and own size will bias together, and give visible feet or a visible height rod so people can re-align.
• Do not run distance-critical tasks (stop on a mark, judge a gap) in a session whose eye height is uncalibrated.
• How to check: the same corridor, calibrated eye height versus a child’s line of sight; blind-walk and “show how tall you are now.” The child condition should walk short or report farther, and show a shorter stature. If only one of the two shifts, that scene is mostly not using this scale geometry.

Related

• Same group: N4.08.1 Without a known-size referent, vision alone cannot judge absolute scale · N4.08.2 A world miniature lets people operate a large environment from a god view · N4.08.3 Extreme deviation from real scale weakens presence · N4.08.4 Scaling the self turns far-field operations into near-field ones · N4.08.5 Once scale is established in a scene, it keeps biasing size judgments of new objects · N4.08.7 Inconsistent scale breaks action expectations
• Nearby: N1.01 Immersion and Presence · N2.04 Direct Grab
• Search terms: virtual scale perception · eye-height scaling · egocentric distance