resolution

[T3D P3D Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

Dang, I posted this to photo-3d by mistake.  Here it is again...

-Jim C.

Lordy, what a lot of topics!  I'm somewhat embarassed that I can't remember
more figures, as I actually helped write a book chapter on exactly this
topic (limitations imposed by optical factors on infant & adult vision)
about 7 years ago.  I plead low caffeine level.

Let's see, off the top of my head:

Re all the schmutz (sp?) in front of photoreceptors:  this has two effects.
One is to reduce the amount of light reaching the receptors via absorption,
I think by roughly half.  The other is scattering, which would hurt
resolution.  In the peripheral visual field, the limitations on acuity are
largely neural, because a single retinal ganglion cell pools signals from a
number of cone cells (which are also larger & more widely spaced than
foveal ones.  The spaces in between are packed with rods, but under
daylight conditions rods are maxed out & the photons that hit them are
effectively lost).  In the fovea, things appear to be arranged pretty
efficiently; the best resolution of the pupil pretty closely matches the
limitations imposed by scattering & cone spacing, and that information is
kept by the nervous system because signals from individual cones are
maintained (they're combined with signals from other cones, but in such a
way that information isn't lost).

One possible reason for having the schmutz in front of the receptors might
be that it has to be inside the eyeball somewhere; if it were behind the
receptors, they'd have to be closer to the lens, their angular subtense
would be larger, angular resolution would be lower, etc.  Probably not
much, though.

Hyperacuity: if you have a high-contrast, extended contour it's possible to
localize it more precisely than you'd predict based on the spacing between
neighboring cones.  This is a slightly different issue from resolution,
which is the ability to detect the contour against the background...

I probably missed something, I really should go back & read that chapter...
:-)

-Jim C.



----------------------
Jim Crowell
Caltech Division of Biology
216-76
Pasadena, CA 91125
Tel: (818) 395-8337
Fax: (818) 795-2397
jim@xxxxxxxxxxxxxxx



------------------------------

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