ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************

On Sun, Jul 6, 2008 at 7:50 PM, <[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
>
>
I'm thinking it's the same afterimage effect that get's you a cyan parrot in
the cage after you look away from the red parrot. The image before you
mouse-over is a color negative (yellow is minus blue, purple is minus green,
etc)  The explanation I read most often is that the original color
"fatigues" the neurons that sense that color.  When you look to a white
background, the white light yields more excitement in the neurons in the eye
sensing the opposite color than those sensing the fatigued color and your
brain interprets that you are seeing the opposite color.
http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/afterimage.html

When you view the afterimage on a black and white image, the shades of grey
give value to the color and make for a much more realistic color image  If
you look to a white sheet after staring at the negative, you should still
see the colors, but it won't be as realistic

-- 
David L. Smith
Da Vinci Science Center
Allentown, PA
http://www.davinci-center.org

Please consider the environment before printing this email.

***********************************************************************
For information about the Association of Science-Technology Centers and the Informal Science Education Network please visit www.astc.org.

Check out the latest case studies and reviews on ExhibitFiles at www.exhibitfiles.org.

The ISEN-ASTC-L email list is powered by LISTSERVR software from L-Soft. To learn more, visit
http://www.lsoft.com/LISTSERV-powered.html.

To remove your e-mail address from the ISEN-ASTC-L list, send the
message  SIGNOFF ISEN-ASTC-L in the BODY of a message to
[log in to unmask]