On Feb 4, 9:49 am, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> On Feb 2, 8:50 pm, Logan Kearsley <chronosur...@[EMAIL PROTECTED]
> wrote:
>
> > A white light source will produce different colors in a thin film
> > depending on the angle of the light source.
> > So, by simply sandwiching a flat retina between a thin transparent
> > layer and a reflector, one could get a very simple eye that's
> > incapable of imaging but which can use color to detect the angular
> > position of a light source (or the source of a shadow).
> > It would, however, be subject to confusion when looking at brightly
> > colored objects- especially other iridescent objects, which might
> > appear to jump around the visual field as their apparent color
> > changes.
>
> I don't think this idea can work unless there's only one light
> source, and it's more or less a point light source. Also,
> in order to get any information at all the color sensors need
> to be filtered to only receive narrow bands of frequencies.
> That means severely limited sensitivity.
It just requires an extremely high receptor density. The problem might
be mitigated by using sensors that receive multiple overlapping
frequency bands, so that color can be determined by what combinations
of sensors fire.
> > So, I wonder if there is any function or environment in which that
> > would not be a fatal flaw. Is there some reason that an alien or
> > genetically engineered creature might rely on an iridescence eye?
>
> Even assuming the iridescence eye works just fine, I don't
> see how useful the information is. Knowing a light source
> is along the surface of some cone doesn't seem as useful
> as, say, knowing whether the light sources is vaguely to the
> left or vaguely to the right. The latter information may not
> be precise, but it's enough to crudely hunt down or avoid
> the light source. With the information your sensor provides,
> you can't even do that.
You *can* do that. Any single point of color will give you a cone, but
there will be an arc of constant color concave towards the light
source with the colors varying differently on each side depending on
whether the angle is increasing or decreasing. So, by combining
information from lots of pixels across the whole eye, you can get
directional information with resolution limited by the number of
different colors you can distinguish.
Thinking on it some more, though, I'm not entirely sure how one would
deal with the superposition of multiple light sources muddying the
pattern. I shall have to ponder this, but for now it seems like the
best you could do is to make the eye fairly small, so you don't even
try to get differential color information across a large surface, and
average color information over the whole surface so that you can say,
for example, lots of red means theres a light source somewhere on
*this* cone, and lack of blue means there's an obstruction somewhere
on *that* cone.
Multiple eyes spaced apart and facing in different directions could
still give you multiple cones, though, so that you can deduce that a
light source or obstruction must lie on the intersection of several
cones. Hm. And I don't see why said 'multiple eyes' couldn't just be
different regions of a single larger eye surface.... Aha! And that
gets you to a single (or two, or maybe three- one on each side of the
animal) large eye surface that can use color information to determine
the angular position of light or shadow sources.
-l.
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