[Pulfrich Effect] Unexpected stereoscopic depth and perceived magnification when viewing repeated UFO patterns

[Nautilius]

I accidentally discovered a strange stereoscopic immersion effect while testing motion clarity on my ASUS 360Hz G-SYNC Pulsar monitor using TestUFO.

I was investigating at what speed stroboscopic stepping stops being noticeable. Starting at around 3000 px/s, I gradually reduced the speed to 480 px/s out of curiosity, alternating my gaze between the stationary synchronization bar and the moving UFO.

At 480 px/s, the UFO was moving slowly enough for me to follow it comfortably. While focusing on it, something completely unexpected happened. After about 3 seconds, the moving image suddenly appeared much farther away but also significantly larger, almost as if my 27-inch monitor had doubled in size. It felt remarkably similar to stereoscopic 3D, despite using an ordinary 2D monitor without 3D glasses.

I'm convinced I would never have discovered this if I hadn't slowed the UFO down enough to maintain such steady visual focus.

What surprised me most was how effortlessly I could examine motion artifacts. Ghosting, strobe crosstalk and subtle differences between individual UFO rows became incredibly easy to distinguish. It felt almost like looking at the same moving image through a magnifying glass. Details that normally require considerable concentration were suddenly obvious.

Initially, entering this state required about 3 seconds of concentrating on a single point. Once I figured out how to reproduce it by slightly adjusting my eye convergence, I could trigger it almost instantly.

Interestingly, once the effect kicks in, I no longer need to stare at a single point. I can freely examine the entire moving pattern while maintaining the illusion of depth and magnification. The moving image feels like a much larger space that I can visually explore.

However, the effect seems to depend heavily on regular, repeating UFO patterns. Switching to a different scene without those patterns immediately breaks the illusion, leaving me with double vision until I relax my eyes. I've tried other motion tests, including SmoothFrog, but couldn't reproduce the same effect there.

The UFOs appear much larger and farther away, while the interface seems closer and sometimes doubled.

I also discovered something particularly interesting when I paused the image. Under normal viewing, I count 11 UFOs, but in this immersive state I see 12. I genuinely cannot tell which one is the additional image. They all look equally real and sharp. Only by counting them do I realize that I'm seeing an extra UFO.

The effect works with Pulsar ON and OFF. Switching between them while maintaining this state makes the difference in motion clarity astonishingly obvious.

I can comfortably maintain this perception while tracking UFOs at speeds up to around 2400 px/s. At 3000 px/s it becomes more demanding, while at 3840 px/s the image can still appear sharp, but the effort required to track it becomes uncomfortable.

My suspicion is that this might be related to binocular free fusion or wallpaper stereopsis, although I have never experienced anything like it before.

Has anyone else experienced something similar?

@Chief Blur Buster, is this a known visual phenomenon? And could this kind of perceived magnification explain why extremely subtle motion artifacts become so much easier to examine?

[Chief Blur Buster]

My suspicion is that this might be related to binocular free fusion or wallpaper stereopsis, although I have never experienced anything like it before.

Has anyone else experienced something similar?

@Chief Blur Buster, is this a known visual phenomenon? And could this kind of perceived magnification explain why extremely subtle motion artifacts become so much easier to examine?

Yes, it's a known phenomenon! Not everyone is affected (Without special glasses to amplify this).

It's called the Pulfrich Effect.

One eye processes slower than the other, creating a stereoscopic difference because of spatial position differences between two eyes, during times when eyes process different times. Every human brain is different, and it's usually imperceptible until you super-focus on synthetic motion tests. Then your personal Pulfrich Effect goes above the noise, and you're witnessing it.

Not everyone witnesses this. Sometimes the Pulfrich Effect is amplified when you wear tinted glasses (darker lens = eye process the image slower). People who have major problems with Pulfrich Effect, can wear compensating glasses (one lens darker than the other) to prevent this stereoscopic effect interference in real life.

Super Bowl XXIII (the USA version of Football) that occured on January 22, 1989 had a halftime special that used the Pulfrich Effect to turn its halftime show into 3D! If you obtained those special light-dark glasses, you could witness the halftime show in 3D! TV cameras panned sideways during the show, to create the 3D effect in anybody wearing these light-dark glasses.

So the halftime show looked normal to everybody, with none of that ugly red/blue that forces you to wear 3D glasses. So in this case, 3D glasses was optional! Was clever.

It was called "Nuoptix".