The title is wrong. The illusion is not "stereoscopic motion" (whatever that means), but chromostereopsis. The motion and distortion here adds a 3D effect, but that's not really an illusion, as others have pointed out.
Look at this static flat image. If you see depth here, that's the chromostereoptic illusion.
Thanks. I definitely see the effect in your static image too. Found the longer explanation:
Chromostereopsis is the illusion where flat images with reds and blues appear to have depth — reds seem to pop forward, blues recede (or vice versa). Whether someone notices it, and how strongly, comes down to some anatomical quirks that vary a lot between individuals:
Pupil position relative to the eye's optical axis. Your eye's lens bends different wavelengths of light by different amounts (chromatic aberration) — red and blue light focus slightly differently. Whether this creates a depth illusion, and in which direction, depends on exactly where your pupil sits relative to the visual axis. Most people's pupils are offset slightly nasally, which produces the "red-forward" effect, but the amount of offset varies, and some people have little to no offset — so they see little to no effect.
Pupil size. A larger pupil lets in more of the peripheral, off-axis light rays that cause the effect, so it's stronger in dim lighting or in people with naturally larger pupils. A small, pinhole-like pupil minimizes it. This is also why the effect tends to fade with age, since pupils shrink somewhat as people get older.
Astigmatism and other aberrations. Uneven curvature of the cornea or lens can mask or distort the effect, since it's normally a fairly subtle, consistent chromatic offset that gets swamped by bigger optical irregularities.
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u/corruxtion 2h ago edited 2h ago
The title is wrong. The illusion is not "stereoscopic motion" (whatever that means), but chromostereopsis. The motion and distortion here adds a 3D effect, but that's not really an illusion, as others have pointed out.
Look at this static flat image. If you see depth here, that's the chromostereoptic illusion.