Re: TECH-3D digest 203

[T3D Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 7:19 AM -0700 9/2/97, T3D Richard Young wrote:
>
>John - In the human fovea (which means "pit"), which is
>the area for maximum resolution, the retinal neurons other
>than the cones are
>off to the side (hence the term "pit"). Our vision
>must not be degraded very far by intervening retinal material since we
>are at the maximum resolution (about 60 cycles per degree)
>allowed by the lens of  the eye. If the lens is by-passed using laser
>interferometry to image directly on the retina, then a much higher peak
>spatial resolution can be obtained, showing that the limiting factors are not
>due to the retina itself.

That's right as far as detection is concerned.  I was pretty imprecise
about this in my last post, but one thing to keep in mind is that studies
of visual resolution often don't care whether you're seeing a pattern
accurately, just whether or not you can detect it.  Under normal
conditions, your cone mosaic isn't exposed to patterns that it can't
accurately represent; they're filtered out by the optics of the pupil &
eyeball.  These laser-interferometry studies showed that if you bypass
those optics, you can detect much finer patterns than you might expect, but
you don't see the actual pattern that's being presented.  In technical
terms, it's aliased; what you see is something like a coarse moire pattern.

So the retinal spacing per se doesn't place a limit on what you can see,
just on what you can identify/recognize...


> Outside the fovea, some diffusion might
>be expected I suppose, but the cones (and now rods) are now spaced
>out more. In other words, eyerthing is matched along the different
>levels to make most efficient use of the resolution that is available.

No, 'fraid not.  Optical resolution in the periphery is much better than
retinal or neural resolution.

-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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