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Dennis,

I don't know for certain but my guess is that this is the after image
effect.  You fatigue the cones in your retina by staring at a color and then
when you look away from it you see the complimentary color.  The cool part
of this refinement of the illusion is that they give  you the black and
white background to  work  with.  The curious part is that if you look away
you see the black  and white image.  I am wondering if you are only using
some of your cones to produce the after image and that if you go off the
spot you see the image normally.

Very cool indeed.

Thanks,

Mike



On 7/6/08 6:50 PM, "[log in to unmask]" <[log in to unmask]>
wrote:

> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related institutions.
> *****************************************************************************
> 
> Dear all,
> 
>  
> 
> My son sent me an optical illusion unlike any I've seen before.  I
> thought you would enjoy it.  Does anyone know what is happening in the
> eye/brain to make this work?
> 
>  
> 
> http://www.johnsadowski.com/big_spanish_castle.php
> 
>  
> 
> Dennis
> 
> "Work hard to find something that fascinates you. When you find it you
> will know your lifework" -- Richard Feynman
> 
> Dennis Schatz
> 
> Senior Vice President for Strategic Programs
> 
> Pacific Science Center
> 
> 200 Second Ave. No.
> 
> Seattle, WA 98109
> 
> Phone - 206-443-2867
> 
> Fax - 206-443-3631
> 
> www.dennisschatz.org <http://www.dennisschatz.org>
> 
> 
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