Connectionists: Physics and Psychology (and the C-word)

[Barak A. Pearlmutter]

Jim,

As a pure aside...

> ... accept (sic) that the Cepholapod retina is pointed in the “right”
> direction - i.e. towards the light source ...

I think this is a bit of a "myth of science".  It is true that the
mammalian retina has the circuitry and blood vessels between the lens
and the photoreceptors, while the cepholapod retina has them the other
way around.  But the conclusion that this is a design flaw in the
mammalian eye is not quite so clear.  There are four advantages that I
know of to putting the photoreceptors behind the circuitry.

(1) If the back of the eyeball is reflective (as in a cat) light gets
two chances to be caught by a photoreceptor.  Resolution when doing this
is degraded if the photoreceptors are moved away from the reflective
surface.

(2) It is easier to keep the sheet of photoreceptors smooth.

(3) If blood vessels are between the eyeball and the photoreceptors, the
heartbeat can make the photoreceptors wiggle.

(4) The photoreceptors are very metabolically demanding, and can be
easier to maintain (nourish, clear toxic wastes) from the eyeball.

					--Barak.
--
Barak A. Pearlmutter
 Hamilton Institute & Dept Comp Sci, NUI Maynooth, Co. Kildare, Ireland
 http://www.bcl.hamilton.ie/~barak/