----- Original Message -----
Sent: Tuesday, November 10, 2009 12:28
AM
Subject: Re: Imaginary colors
Speculation
Alan:
That poses an interesting problem. What kind of
pigments would a
non-human use? I'm think something in UV range made from
fluorescing
minerals or something like that. There are some artist pigments
that
change colors depending on angle of light. Looks way-cool in
gallery.
Move your head a bit and what was one color changes to another.
I'll see
if I can find example from a gallery show we had last
spring.
well here's a little fellow worth looking at - the mantis
shrimp
"Mantis shrimp possess hyperspectral colour vision, allowing
up to 12 colour channels extending in the ultraviolet[10]. Their eyes (both
mounted on mobile stalks and constantly moving about independently of each
other) are similarly variably coloured, and are considered to be the most
complex eyes in the animal kingdom.[11][12] They permit both serial and
parallel analysis of visual stimuli.
Each compound eye is made up of up to 10,000 separate
ommatidia of the apposition type. Each eye consists of two flattened
hemispheres separated by six parallel rows of highly specialised ommatidia,
collectively called the midband, which divides the eye into three regions.
This is a design which makes it possible for mantis shrimp to see objects with
three different parts of the same eye. In other words, each individual eye
possesses trinocular vision and depth perception. The upper and lower
hemispheres are used primarily for recognition of forms and motion, not colour
vision, like the eyes of many other crustaceans.
A colorful
stomatopod the peacock mantis shrimp (Odontodactylus scyllarus) seen in the
Andaman Sea off Thailand.
Rows 1-4 of the midband are specialised for colour vision,
from ultra-violet to infra-red. The optical elements in these rows have eight
different classes of visual pigments and the rhabdom is divided into three
different pigmented layers (tiers), each adapted for different wavelengths.
The three tiers in rows 2 and 3 are separated by colour filters
(intrarhabdomal filters) that can be divided into four distinct classes, two
classes in each row. It is organised like a sandwich; a tier, a colour filter
of one class, a tier again, a colour filter of another class, and then a last
tier. Rows 5-6 are segregated into different tiers too, but have only one
class of visual pigment (a ninth class) and are specialised for polarisation
vision. They can detect different planes of polarised light. A tenth class of
visual pigment is found in the dorsal and ventral hemispheres of the
eye.
The midband only covers a small area of about 5°–10° of the
visual field at any given instant, but like in most crustaceans, the eyes are
mounted on stalks. In mantis shrimps the movement of the stalked eye is
unusually free, and can be driven in all possible axes, up to at least 70°, of
movement by eight individual eyecup muscles divided into six functional
groups. By using these muscles to scan the surroundings with the midband, they
can add information about forms, shapes and landscape which cannot be detected
by the upper and lower hemisphere of the eye. They can also track moving
objects using large, rapid eye movements where the two eyes move
independently. By combining different techniques, including saccadic
movements, the midband can cover a very wide range of the visual
field.
Some species have at least 16 different photoreceptor types,
which are divided into four classes (their spectral sensitivity is further
tuned by colour filters in the retinas), 12 of them for colour analysis in the
different wavelengths (including four which are sensitive to ultraviolet
light) and four of them for analysing polarised light. By comparison, humans
have only four visual pigments, three dedicated to see colour. The visual
information leaving the retina seems to be processed into numerous parallel
data streams leading into the central nervous system, greatly reducing the
analytical requirements at higher levels.
At least two species have been reported to be able to detect
circular polarized light[13][14] and in some cases their biological
quarter-wave plates perform more uniformly over the entire visual spectrum
than any current man-made polarizing optics [15][16]. The species Gonodactylus
smithii is the first - and only - organism known to simultaneously detect the
four linear, and two circular, polarization components required for Stokes
parameters, which yield a full description of polarization. It is thus
believed to have optimal polarization vision
[14][17][18][19]."
