Health - Optical illusion

Never Ending Staircase Illusion

2010-01-24T06:31:00.001-08:00

Neil Rhodes contacted me recently, and suggested we feature some of his realistic photo-shopped optical illusions. As you see, the theme is nothing we haven’t already seen, but the results Neil accomplished speak for themselves. Impossible structures are often posted to this blog, and they usually appear in two separate forms: either as real camera shots (made under proper angle, with no digital manipulation involved) or they are simply painted and don’t exist in real-life. This version is something in between. I can’t recall we had such a realistic digitally manipulated photos in the past. Correct me if I’m wrong. Additionally, Neil included link to one of his tutorials, where he explains in details how you can create a Never Ending Staircase yourself.

More Imposible Stuff by Tabary

2010-01-24T06:29:00.004-08:00

When I wrote my previous post, obviously I forgot about Francis Tabary and his extraordinary sculpture achievements. Luckily (probably motivated by that particular post), Francis contacted me with some fresh works. Most of it we haven’t had the opportunity to publish on our site before. All that you see are real-life sculptures, and can be purchased via Tabary’s website. The secret is that the photo must be taken from exactly the right angle. Perhaps with enough experience, you can visualize how some of these sculptures might look from other angles.

Another thing, I wanted to alert you with: I love all your comments, and regularly go through them to understand how my audience actually breathes. But it feels somehow “lonely” seeing most of you have that anonymous default icon next to your text. I invite all of you, who previously hadn’t already customized their personal avatar, to get one now. Once you set it, all of your comments will have unique and personal photo you choose, placed next to your text. Those of you using Facebook Connect, can ignore this paragraph – you already have your Facebook pic automatically assigned to your account :)

In Which Direction Does It Spin?

2010-01-24T06:29:00.002-08:00

Shown optical illusion just laid there on my hard disk for years. When I opened it today, I couldn’t remember why I placed it in my illusions folder in the first place? After some puzzling, finally I managed to see its visual phenomenon!

Ok, here’s what I want you to do: concentrate on the animated .gif on your right. You’ll quickly realize it represents some sort of see-through sphere, constructed of many dots rotating in one direction. Dots in front make the front face of the sphere, while “background” dots belong to sphere’s back. It’s logical they rotate in opposite directions. Now try and switch those background dots with front-face ones. Notice any change?

If you manage to visualize this, your able to change the direction in which sphere rotates. With some practice, you’ll be able to switch the direction back and forth in very short time fragments. Don’t underestimate yourselves – many individuals have difficulty seeing this type of illusions. It’s not that they’re less worthy, it’s just that their brain operates differently… Which reminded me – did you know that more than 1/3 of all people who went to see Avatar in 3D couldn’t see the image in 3D?

There are many optical illusions of this type available; one of the more popular being Spinning Dancer Optical Illusion. Your best shot of finding more, would be browsing through our Animations category.

Eyes or Eyelids Illusion

2010-01-24T06:29:00.000-08:00

Here’s a funny story: when I first located given optical illusion, I thought it was great, and saved it for one of my future articles (today’s one). There was an interesting article accompanying it, explaining the event when this vintage photo was taken, along with the twist I found fascinating. The problem is, I forgot in which direction did the twist go…

So let me tell you what is happening here, and leave it up to the majority to decide the direction of the twist. I can see the photo realistic in both ways; either as woman with her eyes shut, having her eyelids painted to appear she is staring at us, or the other way round – woman having her eyes opened, but her mascara done in such way, to appear her eyes are shut.

Don’t take me for granted, but I lean more towards the first option. I just know that when I first saw it, the twist was opposite to what I imagined it to be. It’s just that I forgot, and don’t remember what is the proper way of seeing it.

Second Best Optical Illusion EVER?

2010-01-24T06:28:00.001-08:00

Remember the Best Optical Illusion Ever article, posted two months ago? Well, those of you who’ve seen it will have no trouble understanding this one. Rest of you, quickly jump to the prequel post before continuing with this one. Ok, now when you know where this is going, there’s still one additional Easter Egg left. There is a gallery included below, which reveals how this optical illusion came to existence. In my humble opinion, Craig Tracy really deserves being included in some sort of Art Hall of Fame. Did I remind you that what you are seeing is a real life photo? Now for that Easter Egg – count how many individuals were included this time ;)

Body Paint Tiger Optical Illusion - Craig Tracy 1

“Stepping feet” Motion Illusion

2010-01-24T06:27:00.000-08:00

What to do & observe

Fixate off-centre, but observe the blue and yellow patches (‘feet’). Whenever the grid is visible, the feet seem to step out of phase, while in reality their movement is always parallel. Like tiny feet going tip-tap-tip-tap…

Comments

Stuart Anstis first demonstrated this illusion in 2003. Latest pertinent paper: Howe et al., 2006

Level-1-explanation:

Press the “colour off” button. Now it becomes obvious that the edges of the light ‘foot’ merge with the light bars, and are only visible when they traverse the dark bars. So half of the time there really is no motion cue, and perception goes into default, i.e. no motion. For the dark foot the same holds, only at alternate times.

With reduced contrast of the grating (button “contrast –”) isoluminance of edges and grating is no longer present, so the effect disappears.

Level-2-explanation:

Level-1-explanation plus: The edge information is only contained in colour, and the (magnocellular) motion system cannot see it.

Level-3-explanation:

The effect still persists when there is a slight contrast between foot and grating (not shown here). Anstis (2004) attributes this to slowing down of motion under conditions of reduced contrast (Thompson 1982), and goes much deeper into the subject.

The demonstration above was inspired by Stuart’s version. Thanks to Wolfgang Wesemann for first drawing my attention to this phenomenon, and Wolfgang Beyer for bright ideas.

Level-2007-explanation:

Just when I thought this illusion can be rather intuitively understood, there appears this complicated paper Howe et al. (2007), disproving my above thoughts and suggesting a very intricate explanation. Recently, I included this paper in a seminar and we tried to follow its reasoning and evidence. In consequence, my 2008 explanation regresses to level 1 & 2 above.

Sources

Anstis SM (2003) Moving objects appear to slow down at low contrasts. Neural Netw 16:933–938

Anstis SM (2004) Factors affecting footsteps: contrast can change the apparent speed, amplitude and direction of motion. Vision Res 44:2171–2178

Thompson P (1982) Perceived rate of movement depends on contrast. Vision Res 22:377–380

Howe PDL, Thompson PG, Anstis SM, Sagreiya H, Livingstone MJ (2006) Explaining the footsteps, belly dancer, Wenceslas, and kickback illusions. Journal of Vision 6, 1396–1405

Optical illusion By Michael Bach

2010-01-24T06:23:00.001-08:00

These pages demonstrate visual phenomena, and »optical« or »visual illusions«. The latter is more appropriate, because most effects have their basis in the visual pathway, not in the optics of the eye. When I find the time I will expand the explanations, to the degree that these phenomena are really understood; any nice and thoughtful comment welcome.

You may be glad to know: There are no tasteless surprises here; you know, these infantile pranks where you scrutinize a picture and suddenly an ugly face (or the opposite end) screams at you…

Don’t distress yourself if you don’t see the effect described, even if trying carefully. For many illusions, there is a small percentage of people with perfectly normal vision who just don’t see it, for reasons currently unknown.

Most visitors of this site are not vision scientists, so you might find the explanatory attempts too highbrow. That is not on purpose, but, like any science, vision research just is not trivial. So, if the explanation seems gibberish, simply enjoy the phenomenon ;–). Otherwise, there is a short paper: Bach & Poloschek (2006) Optical Illusions primer.

»Optical illusion« sounds pejorative, as if exposing a malfunction of the visual system. Rather, I view these phenomena as bringing out particular good adaptations of our visual system to standard viewing situations. These adaptations are »hard-wired« in our brains, and thus under some artificial manipulations can cause inappropriate interpretations of the visual scene. As Purkinje put it: »Illusions of the senses tell us the truth about perception« (cited by Teuber 1960).

Before we delve in, I’d like to express my thanks to the many visitors who gave overwhelmingly positive @feedback, adding constructive advice on content, style and typography; please do keep it coming! [Or use the new guestbook.] I have also been able to improve explanations when convincing scientific evidence was sent ;-). Yes, it does take sizable resources to set up and maintain this, but it is also very rewarding, bringing me into contact with so many charming people. Should you want to give back, simply link to this page or use the donation link ;-). Any advice iOptical illusions appreciated – and, yes, for a non-native speaker, English does represent sizable challenges.