Seeing is believing

smacl

Or not as the case may be. Slightly off topic, but I saw this video and thought some of you might enjoy it. Look carefully and you'll note the cubes are not actually moving, wonder would it work with statues? 😉

https://www.youtube.com/watch?v=nYGdFQKnKQc

Peregrinus

The cubes aren't moving, but the illusion of movement is not created solely by the arrows. You can establish this by covering up the arrows (e.g. with your thumb); you can still observe the way in which the cubes are apparently moving, and you can see when the direction of apparent movement changes.

I'm pretty sure that this is an artefact of the black/white colour changes. I think these don't happen simultaneously at every point; there is a slight gradient whereby the colour change "washes" very rapidly in a particular direction, and it's that which creates the illusion of movement.

Could you use a similar technique to generate apparent movement in a statue? It would be difficult and of limited effect, I think. Firstly, the cubes are simple two-dimensional line drawings with no features other than colour, displayed against a featureless background. There's nothing in there to counter the illusion of movement created by the colour changes. That wouldn't be the case with a three-dimensional statue in a real-world setting. Secondly, you'd presumably effect the colour changes not by getting the statue to change colour from within, but by directing moving lights it. But inevitably, those lights would also shine on the background and surroundings of the statue, which makes it hard for them to have the effect of making the statue appear to move relative to its background.

Having said all that, a technique of this kind can be used to create illusions for stage shows, magic shows, etc. It requires overall dim lighting, and an object displaying against a dark, featureless background, preferably some distance away. And the effect produced is not so much "Oh my God! It's moving!" as "Did it move? Yes? No? God, y'know, it can't have! And, yet . . ."

smacl

Agree entirely with your synopsis on how the colour washes are fooling the brain into seeing movement that isn't actually there but remain fascinated by it in terms of misconceptions on how we perceive motion. I did a course a couple of years ago on computer vision for AI and would guess you could achieve a similar kind of illusion using shadow play on a human face. What the above optical illusion and others like it show is how much of what we see is actually the brain filling in gaps for what it thinks we should be seeing, based on various visual cues, rather than what is actually there.

volchitsa

Also, hadn't the people seeing the statues move stared directly at the sun beforehand? Or am I confusing that with some other "miraculous" appearance in Ireland in recent years?

If they had been though, that could surely cause some sort of visual disturbance as powerful as the cubes above (and well done for showing us that, BTW - it's excellent.)