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Help: Optical Illusion Insight

swifty

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Jul 7, 2006
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Hey guys,

I was wondering if any of you could offer some insight into the world of optical illusions. I love optical illusions and similar such things, but as a skeptic I'm always asking myself "why" I am seeing what I am seeing.

As I have no real knowledge in the area, I can never answer this question sufficiently.

So anyone with some expertise/knowledge in this area could you offer me some help/suggest any reading?

For starters, specifically what is going on in this optical illusion.

image.gif


Why do we see green when focusing on the cross? And why do the purple dots disappear when focusing on the cross?

This is all I figured out, they only disappear if you are stationary whilst looking at the cross. If you move forward or back they re-appear, so I'm thinking it's something to do with the focus of the peripherals.. but yeah, I have no real knowledge haha.

Any help is much appreciated.
 
Image persistence.

Your eye gets used to seeing pink, and fills in the anti colour, in this case green.

Not sure of the exact mechanism, but that's the basic idea.
 
I've seen this before. But it's SOOOO cool. It's neat, then the red spots disappear and it's even cooler.
 
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Hi

Neural fatigue.

If you move your eyes around, you're using different sets of cones to detect the colors, so the fatigue effect doesn't come into play. If you'll notice: When you first start looking at the sample, it takes a moment before you start seeing the green.

After a while, when the purple is extinguished, with purple being a mixture of red and blue, the red and blue cones are fatigued, so you pick up less red and blue, you see? The green cones are still fresh, though, so you get a full signal from them, so the color seems to be greener.
 
Then, eventually, the pseudo-green becomes fatigued, and you are left with the neutral gray of the background, which is why they seem to disappear.
 
Thanks for all the help so far guys! Just one gap I don't quite understand yet.


I still don't quite understand the following.

"After a while, when the purple is extinguished, with purple being a mixture of red and blue, the red and blue cones are fatigued, so you pick up less red and blue, you see?"



How is the purple extinguished and what causes the fatigue? The cones which detect purple [red and blue cones] can only last a while detecting the colour until they get fatigued and need to recover?
 
swifty said:
Thanks for all the help so far guys! Just one gap I don't quite understand yet.


I still don't quite understand the following.

"After a while, when the purple is extinguished, with purple being a mixture of red and blue, the red and blue cones are fatigued, so you pick up less red and blue, you see?"



How is the purple extinguished and what causes the fatigue? The cones which detect purple [red and blue cones] can only last a while detecting the colour until they get fatigued and need to recover?
Click to expand...

I think the purple gradually fading after staring at it for a while is down to adaptation of the neurons that percieve the stimulus, rather than fatigue of the cones:

http://en.wikipedia.org/wiki/Troxler's_fading

(edit: unless you are talking about the dots disappearing one at a time round the circle, in which case it happenes because that is what you are actually being shownon the screen. On googling I was surprised to see so many people that thought this was actually part of the illusion)

Here's another great disappearing dots illusion:

http://www.michaelbach.de/ot/mot_mib/index.html
 
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Professor Yaffle said:
I think the purple gradually fading after staring at it for a while is down to adaptation of the neurons that percieve the stimulus, rather than fatigue of the cones...
Click to expand...
I thought the photopigments (the color opsins) were responsible here.
 
Hi

Photopigments have a pretty high rate of regeneration, but neurons adapt and fatigue very quickly. (Okokok - My memory of a class in Clinical Psychology back in College.)

That's why an incredible and nauseating stink, after just a few seconds, just seems to go away. My brother's feet, fresh out of the sneakers, for instance: I wouldn't smell anything, after a bit, but people coming into the room would wrinkle up their noses and go right back out.

In your eye, you have detectors (cones) for red, blue and green.

cs_RGB.gif

Stare INTENTLY at the white Wankel-rotor in the middle of the above picture for several seconds, then look quickly at the white-space to the right.

SURPRISE!!​

Purple/magenta is a mixture of red and blue. The complimentary color (the one left out) is green. When you look at a purple/magenta object for a bit, the red and blue transmission lines get tired and, since it's not moving, your body goes along with the tiredness, just in case a... say... sabertooth tiger jumps out, you'll be ready for the new motion and color, which will then draw your attention, the purple/magenta bits having been, by that time gotten-used-to.

This lets you see the new color... say... call it, "sabertooth-biting-through-your-parietal-lobe brown," more easily and take suitable activities to reduce damage to said parietal lobe.
 
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Gagglegnash said:
Hi

Photopigments have a pretty high rate of regeneration, but neurons adapt and fatigue very quickly. (Okokok - My memory of a class in Clinical Psychology back in College.)...
Click to expand...
Neurons have an absolute and relative refractory period when they must repolarize through the action of the sodium pump to be able to fire again. The absolute refractory period is about 1 msec for many neurons. They don't really adapt and fatigue.
This is only analogous to the chemical reaction of the photopigments which are transformed into different molecules ("bleach out") when hit by photons of the appropriate wavelength and then reform. The phenomena of dark adaptation, light adaptation and negative aftereffects all occur at the the level of the receptors and involve photopigments.
 
Hi

Jeff Corey said:
Neurons have an absolute and relative refractory period when they must repolarize through the action of the sodium pump to be able to fire again. The absolute refractory period is about 1 msec for many neurons. They don't really adapt and fatigue.
This is only analogous to the chemical reaction of the photopigments which are transformed into different molecules ("bleach out") when hit by photons of the appropriate wavelength and then reform. The phenomena of dark adaptation, light adaptation and negative aftereffects all occur at the the level of the receptors and involve photopigments.
Click to expand...


Thanks. Live and learn.

Now that you mention dark adaptation, I remember, in the Army, being told about, "visual purple." I wish I'd remembered that before spending all that making an incorrect answer!

D'OH! (_8(|)
 
Gagglegnash said:
[qimg]https://home.comcast.net/~alsohlstrom/cs_RGB.gif[/qimg]
Click to expand...
All I can say about that image is anyone who works in the graphic arts/publishing/printing business will recognize it as showing the relationship between the RGB additive colour model and the CMYK subtractive colour model.
 
Hi

Corsair 115 said:
All I can say about that image is anyone who works in the graphic arts/publishing/printing business will recognize it as showing the relationship between the RGB additive colour model and the CMYK subtractive colour model.
Click to expand...


...and, in the eyeball color sensing model, that red and blue make up the purple/magenta, right, and that the green isn't involved with the purple/magenta (complimentary color).
 
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