Lightness and Brightness and Other Confusions

The domain of colour psychophysics can extend beyond mixing and matching
to the whole set of behavioural responses to spectral stimuli. So understood,
it could be extended to animals and machines. It is strictly third-person in
perspective and treats the subject as a black box. Its aim is to discover patterns
of reliable response to a controlled set of targets. Computational modellers
can then develop a set of functions that will translate those inputs to their
associated outputs. The set of functions could be realized in either hardware
or wetware, depending on the nature of the system that is being modelled.
Although the data may be artificially structured in earlier stages of development,
the aim of the modellers is to refine their product so as to approximate
ever more closely the conditions of the setting in which the modelled object
either does operate, in the case of a natural system such as a honeybee, or is
intended to operate, as in the case of a robot.
Now suppose that we have a robot capable of operating effectively in a natural
visual setting. It derives shape from shading, recognizes occluded objects,
sorts paint chips, separates luminance from reflectance, and so on. In short, it
deals with the environment of spectral power distributions in much the same
way as we do. Does it see colour?
If your answer to this question is “yes”, you will accept physical and psychophysical
colour and take psychological colour to be a mere appearance. But if
your answer is “no,” you will not only take coloured shadows to be truly coloured,
you will regard physical colour and psychophysical colour (which is
really physical colour that is filtered by a receptor apparatus) as not being
full-blooded colour at all, but merely the normal stimuli for psychological
colour, that is, colour as an experienced quality. Inevitably, this demands a
first-person perspective, the view from within the black box.
Life inside the box can be pretty nice. In contrast to the cold impersonality of
atoms and the void, it is quality rich and, well, colourful. The box provides not
just a sensory rush, but a structured and supplemented array as well. Outside
there is light and darks, but the inside adds whiteness and blackness. Outside
there is a wavelength continuum, but inside there is a configuration of unitary
and binary hues.
This is, of course, just a latter-day version of what the philosophermathematician
Whitehead called “the bifurcation of nature.” It was introduced
into Western culture by Galileo and Descartes, and philosophers have
been trying to bridge the divide ever since. It would be both presumptuous
and vain to undertake here the construction of yet another bridge, but it
might be interesting to consider some aspects of the problem from the standpoint
of colour studies.
First of all, the human body, including the nervous system, is a part of nature;
it is made of the same stuff, and subject to the same laws. It is becoming in-
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