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From: daemon@decwrl.UUCP
Newsgroups: net.followup
Subject: Re: Are you seeing pink walls?
Message-ID: <4597@decwrl.UUCP>
Date: Wed, 14-Dec-83 11:56:59 EST
Article-I.D.: decwrl.4597
Posted: Wed Dec 14 11:56:59 1983
Date-Received: Fri, 16-Dec-83 03:41:56 EST
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Organization: DEC Western Research Lab, Los Altos, CA
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From: Joe Falcone HLO2-3/C09 dtn: 225-6059 <erlang::falcone>
CC:	 


I don't claim to be an expert on the matter, but a a year ago I spent
a few months studying color vision (in particular, the perception of
color vs. black-and-white images on computer displays), and the one thing
that amazed me about the field was how little we know for certain about
the mechanisms of color vision.  There are many theories, but very little
evidence (since that would involve possibly destructive experiments).
The following is a capsule of some theories.

The theory proposed by Rick Wise is off the mark to begin with.  The human
eye does not work like a TV camera - and in fact few eyes in nature do.
Instead of red, yellow, blue and intensity receptors, the eye has red
and green receptors for bright light, intensity receptors for dim light,
and there is some debate as to whether we have blue receptors at all
(there are some visual tricks which can be explained by that).

Hence, a workable theory (and one that I believe has been supported by
some laboratory tests) is that under strong influence, a receptor can
be suppressed, so that when the stimulus is removed, the other (or
opponent) receptor begins showing a response that is greater relative
to the other one.  SO the green receptors are suppressed, and when the
stimulus is removed, they shut off MUCH MORE than the red receptors do
(since they are "exhausted" from the stimulus), so that the red receptors
are providing relatively more input than the green receptors.
Voila - Pink Walls!

If anyone out there has a red phosphor terminal, I'd be interested in
knowing whether the walls appear green after extended use.  Notice also
that this explains why users of blue phosphor terminals don't see orange
or red/green walls - blue receptors are not that important to color vision
and blue tends to stimulate/suppress red and green receptors equally.

Joe Falcone
decvax!decwrl!rhea!erlang!falcone
DEC Research, Hudson, MA