Optical Illusions part 3 (⊙▂⊙)

♥ Leaning Tower Illusion 
 What to see After the initial animation you see two towers on the buttom. They do not seem to be parallel, the right one leans to the right. What to do If you press the button ‘move’ then the two towers will slide on top or each other. Obviously, the two towers are identical! So how can they lean? Press ‘move’ again to disengage. You might want to try to adjust the angle of the left button with the circular slider, but when they seem roughly parallel the aren't when moved on top of each other.

This beautifully simple effect was reported by Kingdom et al. in 2007. As they write in their paper “The explanation for this illusion would seem to be straightforward”: If in reality we see two towers next to each other (see the lower figure for the full picture), all elements of the figure must have the same perspective vanishing point. When we simply duplicate one tower and translate it, this also translates the vanishing point for the duplicated tower. So, if in reality we would see two adjacent towers with different vanishing points, then they would acutally be leaning. So one could say this is no illusion after all! The original version, using the leaning tower of Pisa, won first prize in the Illusion-of-the-year contest 2007. My tower example happens to be the Sheraton in Chongqing. While it looks leaning, it isn’t, that’s just a consequence of camera position relative to the center combined with the laws of perspective.

 ♥   Moon Illusion

The “moon illusion” consists of two phenomena:
(1) the moon appears larger than it actually is, and
(2) this enlargement is much stronger on the horizon than at the zenith.

Generally, any celestial objects near the horizon looks larger than when the same object is high on the sky. The moon in the neighbouring picture is of “aesthetically correct” size. By placing the mouse over the picture the actual size is seen (pictures from Rock 1984, based on the painting by Honoré Daumier »O Lune! … Inspire-moi ce soir quelque petite pensée…« 1844). Comment. The moon illusion is usually explained through size constancy, with the necessary additional assumption that the ‘default’ distance for any object is less than the horizon/skyline distance. Amazingly, when you bend over and look through your legs, the moon illusion is greatly diminished (Coren 1992, Higashiyama & Adachi 2006)! This underscores the influence of context on size constancy.

♥  Hering Illusion

The standard Hering illusion (1861). Placing the mouse over the image causes the oblique lines to disappear, revealing the fact that the red bars were completely straight all the time.

The picture on the top is a mess to look at. But if you place the mouse over it, you can see how beautifully it changes the apparent orientation of the red squares. This is a dynamic variation of “Three in One” by Hans Kuiper which, in turn, is based on “Square of Three” by Reginald H. Neal (colour lithograph, 1964).

♥  Müller-Lyer Illusion

I hope you have enjoyed the “Müller-Lyer Illusion” (1889). When one bisects the horizontal line it is quite normal that large errors are made, so don’t be annoyed or disappointed (I err by at least 1 cm). This phenomenon is placed in the category “size constancy” because I find the perspective explanation (see bottom) very convincing. Müller-Lyer's original figure showed two double-ended arrows, here I used the Brentano variant.

picture 1

Picture 2

The German satire-magazine ‘Pardon’ published in ≈1970 an article on this illusion. It was accompanied by the two pictures on the right, demonstrating a Müller-Lyer effect on enclosed objects ;-). [The picture 2 of elephant not only looks larger, but also happier…]

♥  Ramp aftereffect

Warning: this is a subtle effect. Gaze for at least 10 s at the fixation cross in the neighbouring dynamic image. This will adapt your eyes to a brightening patch (above) and a repetitively dimming patch (below). Then move the mouse over the panel to turn it into a steady gray. You should see an aftereffect of apparent dimming (above) and apparent brightening (below). Move the mouse away to re-adapt. This demonstrates the existence of transient visual pathways selective for gradual changes of luminance.

♥  Wertheimer-Koffka Ring

Warning: this is a subtle effect. Compare the two halves of the ring. The left half looks subtly darker than the right one. Now move the mouse over them… You may need to change your observation distance to see a sizable effect. Comment. In the presence of the bar, the brightness difference without luminance difference is a standard case of simultaneous contrast. This is probably due to retinal mechanisms. Without the bar, filling-in (a cortical phenomenon) ‘wins’.

 In the next post, i will give you some video about optical illusions... See you then.. (●*∩_∩*●)

 GBU ^_^