Re: Color constancy

[John Denker <jsd@MONMOUTH.COM>]

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 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.

Never mind two viewers -- consider only one viewer.  If you have the _same_
viewer receiving the _same_ wavelength under different circumstances (e.g.
different illumination), the perception may be radically different.

This is an important point.  Textbooks commonly get it wrong.


> 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.

  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