Lightness and Brightness and Other Confusions

limited to what is required for human life and survival. Gibson describes our
senses as perceptual systems: instead of five separate senses he prefers to talk
about five modes of external attention. (Gibson 1966, pp 166-167) MANFRED
ZIMMERMANN 25 estimates the potential capacity of the human visual system at
10 million bit/second (which would mean the ability to discriminate 10 millions
colours). In information theory the concept bit is used as a measure of
quantity of information; it indicates a smallest perceivable unit in the information
flow. It does not describe content of information only perceivable
quantity of information. The total information capacity of all senses together
is supposed to be about 11,2 million bit/second and the information capacity
for our conscious experience of the world around is not more than 40
bit/second. (Zimmermann 1989, p 172). Principles for selection and reduction
of information correspond to human existential needs. Every creature
has its own special access to the world. William James compares the work of
our senses with the work of sculptors:
Other sculptors, other statues from the same stone! Other minds, other
worlds from the same monotonous and inexpressive chaos! My world is
but one in a million alike embedded, alike real to those who may abstract
them. How different must be the worlds in the consciousness of an ant,
cuttlefish or a crab! (James 1890, pp 288–289).
Reducing information and selecting what in a given context has to be attended
to requires some kind of attention structure. An attention structure –
conscious or unconscious – directs attention to certain aspects of a phenomenon.
In science such a perceptual principle is usually called a theoretical
perspective. (Eneroth 1994, p 24). Acquiring knowledge is to develop attention
structures. (Gardner 1994, p 24).
Merleau-Ponty discusses how we experience the surrounding world in different
ways depending on situation. He makes a distinction between two modes
of attention: the reflective attitude and living perception. (Merleau-Ponty
2002, p 355). This distinction is significant to our perception of colour.
Strictly speaking it is not possible to find out how we perceive colour in living
perception, since every question that directs our attention towards a colour
gives, of necessity, rise to a reflective attitude.
When perceiving colours, our vision does not recognize the absolute intensity
or the absolute spectral distribution of radiation that reaches our retina. Instead
distinctions and relations are registered. Our visual system is developed
for a continuous spectrum of light and gradual changes between different
illuminations, and under these circumstances we perceive colours as more or
less constant. Our visual sense adapts to current light conditions: what we
perceive as white in a given illumination functions as a perceptual “anchor”
25
German neurophysiologist, 1933–
23