ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************
Here is the explaination that has been sent out to my neuroscience
graduate programs listserve by a fellow grad student:
1 There is something called the "negative retinal afterimage".
It becomes visible when one given hue stays on the same retinal position
for several seconds (usually we would move our eyes typically 3 times
per second, so this is not disadvantage in normal viewing). The
afterimage builds up as that retinal location adapts to this special
hue, and when looking at a neutral background the complementary colour
is seen.
2 This is a good thing, normally, because it helps "colour
constancy", that is we see colours somewhat independent of the ambient
illumination (compare the bluish glacier noon sun with a reddish tint in
the evening living room by the fireside).
3 Ok, so the afterimage is "burnt in", that is that retinal
location is adapted. Now the magenta patch is suddenly switched to grey.
Because of the adaptation, the complementary colour is now seen, which
would be green for magenta, or light grey for a dark grey.
4 The retinal afterimage typically fades away rapidly (over a
few seconds under normal conditions). But here this fade-out does not
reduce the perception of the afterimage, because a new one is uncovered
right after at the next location.
5 In addition, a Gestalt effect, here the "phi
phenomenon" comes into play: the afterimage from the successive retinal
locations is integrated and perceived as one single moving object,
namely the green disk.
6 In summary, the following factors make this illusion rather
compelling:
* it is rather easy to steadily fixate on the centre
* most of the time the retinal locations are re-adapted and
the afterimage is uncovered only briefly
* a Gestalt effect leads to the perception of a flying green
disk.
On Fri Nov 4 9:47 , jeff courtman sent:
ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************
Ok, I'll bite...i think I understand the dots disappearing; kind of like
the cheshire cat exhibit - you're brain keys on the movement at the edge
of your peripheral vision....and I assume the green is the complimentary
of the pink, but????
Jeff Courtman
Exhibits & Special Projects Coordinator
251.208.6851
www.exploreum.org
***********************************************************************
More information about the Informal Science Education Network and the
Association of Science-Technology Centers may be found at http://www.astc.org.
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]
***********************************************************************
More information about the Informal Science Education Network and the
Association of Science-Technology Centers may be found at http://www.astc.org.
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]
|