AbilityBenchDepth perception test built from the cues a flat screen can actually carry
Two shapes appear side by side and you say which is nearer. Four cues take turns being the only difference between them — relative size, occlusion, texture scale and motion parallax — and each is scored on its own. No glasses and no calibration step; what it cannot measure is stereo depth, because a display is one flat surface at one distance and gives your two eyes nothing to disagree about.
Two shapes appear side by side and you say which of them is nearer. Nothing is timed and nothing is hidden after a second: the pair stays on screen until you answer. The first 6 pairs are deliberately ambiguous and are not marked right or wrong — they exist to find out which cue you follow before this page has told you what any of the cues mean.
What a screen can and cannot ask you
Your two eyes sit ≈ 63 mm — Dodgson (2004) apart, and stereoscopic depth comes from the small difference between what each of them sees. A monitor is one flat surface at one distance, so both eyes get the same picture of it and that difference is zero. Every trial here is therefore a pictorial cue — one that works in a painting, a photograph and one open eye. If you want the measurement that needs the two eyes to disagree, it is the stereopsis test, and it cannot start until you have told it your screen size and how far away you are sitting.
Answer with ← and → for the nearer side, or tap the two buttons under the field. One eye is enough for all of it — closing an eye changes nothing here, which is the point.
Depth on a screen, asked plainly
Can a screen test depth perception at all?
It can test the pictorial half and not the binocular half. Depth information splits into cues that survive a photograph — size, overlap, texture, shading, perspective, motion — and cues that need two eyes receiving different images. A monitor is a flat plane at one distance, so both eyes get the same picture of it and there is nothing for the second kind to work with. This page measures four cues of the first kind, one at a time; the stereopsis test has to manufacture two different images before it can measure the second.
I have almost no vision in one eye. Is this test meaningless for me?
It is the one depth measurement on this site built for exactly that case. Every cue here works in a photograph, so closing an eye changes nothing measurable, and people with one working eye read pictorial cues as well as anybody. What a strong result here cannot be is evidence that the eyes work together — the two faculties are separate and this page only sees one of them.
Why does it ask the ambiguous pairs before explaining anything?
Because telling you what a cue means destroys the measurement. Once a page has said that the larger of two shapes is nearer, an answer that follows size might be perception or might be memory of the sentence. The opening pairs put two cues in opposite directions, in silence, to see which one actually drives your judgment; they have no correct answer and the result reports them as a preference, not a score.
What the four cues are, and how small they get
| Relative size | Two discs of different diameter; the larger is read as nearer. Diameter ratios of 1.05, 1.12 and 1.26 |
|---|---|
| Occlusion | One disc covers part of the other, marked only by an interrupted outline. Overlaps of 3%, 8% and 20% of a diameter |
| Texture scale | Two equal silhouettes filled with dots of different size; coarser is read as nearer. Element-size ratios of 1.16, 1.4 and 2.0 |
| Motion parallax | Both discs sweep side to side on one 1.9-second period; the wider sweep is read as nearer. Excursion ratios of 1.16, 1.45 and 2.1 |
Isolating a cue is the hard part of building this. Remove one and you often create another: keep two screen sizes equal to control for size and you have told the observer that the far shape is physically larger. So each pair is identical in every respect but the one being measured — same height, same fill, same stroke — and three of the four quantities are ratios, which survive any screen size, distance or zoom. Overlap is the exception: a fraction of a disc covers fewer pixels on a phone, so compare that row against your own earlier run on the same device. Putting two cues in conflict and reading the weights off the answers is the method of Landy et al. (1995), Measurement and modeling of depth cue combination: in defense of weak fusion, Vision Research.
What leaves with the second eye
No cue is best in general, only best at a distance — the ranking set out in Cutting & Vishton (1995), Perceiving layout and knowing distances, in Perception of Space and Motion. Occlusion is exact at every range and says nothing about how far. Size and texture carry across the whole range but assume the two objects really are alike. Binocular disparity is the one cue a screen cannot keep, and the reason is geometric: your eyes are ≈ 63 mm apart (Dodgson (2004), Variation and extrema of human interpupillary distance, SPIE Stereoscopic Displays and Virtual Reality Systems XI), stereo depth is built from the difference between the two views that separation produces, and a flat panel shows both eyes the same surface. That is what the stereopsis test has to manufacture with glasses or free fusion. For the same reason this page prints ratios and refuses arcseconds: an angle needs a pixel width and a viewing distance that nobody here asked you for.
This is a measurement exercise, not a clinical assessment. It reports what you did on this page against a stated reference and nothing more — it cannot establish reduced depth perception, a squint, amblyopia or anything else about your eyes. Only a qualified professional, working with more than a browser, can make that judgment.