I ask students to recall their disappointment when looking at a
photograph taken inside without a flash (i.e., under the "yellowish"
spectrum emitted by incandescent lights) when they "see" that
everything is "yellowish". I inform them that that color is the
"actual" color (i.e., the camera doesn't "experience" constancies; and
that the reason we don't see the differences is exactly because our
perceptual system is affected by constancies.
On Feb 7, 2007, at 7:52 AM, Marc Carter wrote:
Oh, and strictly speaking, what we perceive as, say, "bluish," doesn't
completely result from a relative reflection of short-wavelengths and
absorption of the longer. Do some color-constancy reading, and things
get much more complicated. I can see a pair of jeans as blue when
they are reflecting wavelengths that in other circumstances would make
something appear quite reddish.
Color perception -- even the perception of "black" -- depends on the
illuminant, the reflectance spectrum (or conversely, the absorption
spectrum) of the surface, and the absorption spectra of *other nearby
surfaces*.
m
PS The constancies are *fun* to demo for your classes. You can
change the character of the illuminant in a classroom usually pretty
easily: go from overhead flourescents to the light from a transparency
projector to daylight from the windows. All are different and thus
the light reflected from surfaces in the room will have to change, and
yet the colors of the objects in the room won't -- as long as the
illuminant is relatively broadband. Narrowband lights, like LASERs,
screw up color constancy. You can also mess with it if you can get a
different light to shine on only a small region of a scene that is
illuminated by a different light -- but that's harder to do in a
classroom.
-------
"Mauchly's Test of Sphericity:
Tests the null hypothesis that the error covariance matrix of the
orthonormalized transformed dependent variables is proportional
to an identity matrix."
---
SPSS
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Tuesday, February 06, 2007 7:12 PM
To: Teaching in the Psychological Sciences (TIPS)
Subject: [tips] question about color perception
Sorry for the cross-posting.
After I explained that when we see a color, that color is what is
reflected after the other wavelengths are absorbed by the material,
one of my students asked about the perception of black. She wanted to
know if it is similar to the black pupil in the eye, which is actually
a hole. If it is the absorption of all wavelengths, how is it possible
to have many shades of black? I told her I would seek the expertise
of my colleagues.
Riki Koenigsberg
[EMAIL PROTECTED]
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========================================================
Steven M. Specht, Ph.D.
Associate Professor of Psychology
Utica College
Utica, NY 13502
(315) 792-3171
"Mice may be called large or small, and so may elephants, and it is
quite understandable when someone says it was a large mouse that ran up
the trunk of a small elephant" (S. S. Stevens, 1958)
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