Thread: Visual Phenomena & Optical Illusions

Originally Posted by Xei

Never seen the faces one before. It's amazing. And such a great demonstration of how the brain works. Thanks.

Thanks - they are really impressive - and I almost didn´t go away from the screen and tried it out when I first saw it.

smile.gif

Originally Posted by GigaByte777

You can change the direction if you concentrate.

Yepp!

Originally Posted by Dianeva

I've been seeing the dancer one so frequently the last few years it's getting boring. And yes, I can switch its direction over and over if I concentrate. This one remains my favourite. I used to have it as a desktop BG and would RC every time I saw it, leading to my first LD.



Everyone's seen the dancer, but has everyone seen the spinning cat!? You can produce the effect with any silhouette. This one is a bit trickier to turn around because there's no shadow.
EDIT: Wtf... what's weird about this one is, whenever I look away from it but keep it in the corner of my eye, I see it moving clockwise, but I can't look directly at it without seeing it counter-clockwise.

I like these Kitaoka snakes as well - he made lots of anomalous motion and other illusions ..
But how cool is that - you used it as RC and had your first LD with it!!



And yeah - I should have looked for a less overused silhouette illusion - liking the cat!
I can stabilize both directions so that they stay, whether I look directly at it, or more peripheral - also by changing where I have the cat in my field of vision.


Made me laugh:



This one is quite flashy:




I´ve been doing the following as a kid - you people probably did too.
It seems it got a name and a paper has been written on it in 1928 by one Sharp.
Hopefully it´s not boring.
What I find really fascinating is that you can do what you want - fingers 2 cm apart, fingers touching, back and forth - you will always have a sectioned sausage between the finger-tips - no normal merging when the focus is off.

Originally Posted by michaelbach.de

The Notorious Frankfurter Illusion





What to do & see

If you have two roughly equivalent eyes you will see a ‘sausage’ floating in front of you in mid air, by following these steps:

Hold your hands in front of you, at 20–30 cm distance from you, at eye level.

Point your index fingers against each other, leaving about 2 cm distance between them.

Now look “through” your fingers, into the distance behind them.

The sausage should appear now, and you can change its length by varying the distance between the finger tips.

For most observers, the sausage will look blurred, at least initially.

If you try to look at the sausage, it will disappear, it is only present if you look at something more distant than your fingers.

It helps if the background is rather homogenous and has a color very different from your fingers.


Comment

Basically, this ‘sausage’ is caused by two mechanisms, (1) physiological double images and (2) interocular rivalry and suppression.


When you look at your fingers, the gaze direction of your two eyes is angled towards each other, so that their lines of sight meet at the target. When you then look into the distance, your eyes shift slightly outward, making their lines of sight nearly parallel. For close objects the image in the two eyes is consequently no longer at the right position, the images are no longer merged and can appear double for your “inner eye”. This is quite normal and occurs all the time, usually these double images are suppressed. So, if the two images overlap, why then doesn't the compound image look like the figure below?




At the end of the image of each finger, there is a rivalry between the image from the two eyes when the brain tries to combine them. In one eye the finger ends, in the other it continues. So what does your brain do in such rivalry situations? If the two images are rather similar, the percept can oscillate between the alternatives. Here, however, we have a high contrast step in one eye, namely the end of the finger, where it is replaced by the background. In rivalry the eye with the higher contrast wins, at least locally; this is here meant by the term ‘suppression’. In the figure on the left this high contrast step is symbolised by the yellow halo.