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Re: Color constancy



At 4:37 PM -0500 11/1/00, John Denker wrote:
At 01:17 PM 11/1/00 -0700, Larry Smith wrote:

But you haven't made a case for it varying from person to person (assuming
they have the same chemicals in their retina).

I didn't try to make that case. But since you ask... I will take up that
question below.

But first a reminder: The remark that started this thread referred to
wavelength.

The remark that prompted my question was not the original "Is white a
color?" thread, but Jim Green's comment that "...we all receive the same
wavelengths but likely we do not all perceive the same colors." I wasn't
arguing against the nonlinear nonlocal aspects of perception; I was only
asking why Jim said it was "likely" that color perception varies from
person to person.

The point remains that the perceived color of an object is
_not_ simply determined by wavelength of light received from that
object. The eye+brain system is not a photometer.

I'm not arguing that the eye+brain system is a mechanistic photometer that
merely records intensities of various wavelengths. But however the
eye-brain system works (the physiology), isn't it the same for all of us
(minus the color-blind)?

Never mind two viewers -- consider only one viewer.

But the two viewers was my whole question. The one viewer wasn't.

If you have the _same_
viewer receiving the _same_ wavelength under different circumstances (e.g.
different illumination), the perception may be radically different.

I won't argue this, but it also doesn't address my question.

Why would you perceive a different color than I do under identical
circumstances?

The answer depends on what we mean by "circumstances".
a) If the wetware is identical, and the circumstances are identical, and
all other factors (including history and psychology) are identical, then
the results ought to be identical in some sense. Duh.

Now we're getting somewhere.

First, does everyone agree with the "duh"?

b) OTOH there are various simple ways to modify a person's
perception. The effects persist longer than you might think. The
existence of such effects means that even if _current_ external
circumstances are identical, you and I could perceive things differently
depending on personal history.

Example: the McCollough Effect, as discussed at:
http://cm.bell-labs.com/who/ches/me/index.html

Ahh, you finally address my question. But overnight isn't a really long
time. Would you agree that two people looking at Herb's grass in the
spring and both calling it green have similar physical things going on in
their eyes and brains? (And minds? Are minds merely brains? Or is the
mind a non-matter thing not identical with the brain? I know this is
getting pretty philosophical here.*) Or is it possible that they might
both use the word "green" but one is really sensing a very different color
than the other?

Thanks,
Larry


* Today's AJP (page 1063) had the following about philosophers:

"You speak of the illumination provided by poets, and although poets may
aspire to understanding, their talents are more akin to entertaining
self-deception. They may be able to emphasize delights in the world, but
they are deluded if they and their audience believe that their
identification of the delights and their use of poignant language are
enough for comprehension. Philosophers, too, I am afraid, have contributed
to the understanding of the Universe little more than poets. They have
raised questions, examined the frailties and imprecisions of human
languages, and have worried a great deal about what may be a question, but
they have not contributed much that is novel until after novelty has been
discovered by scientists."

P.W. Atkins, "The Limitless Power of Science" in Nature's Imagination--The
Frontiers of Scientific Vision edited by John Cornwell (Oxford University
Press, New York, 1995).