Re: TECH-3D digest 203

[T3D Richard Young <young@xxxxxxx>]

>From: T3D john bercovitz  <bercov@xxxxxxxxxxx>

>So light has to go through all the neurons and ganglia
>and stuff, about 100 microns of it, before it reaches
>the rods and cones, which I believe are 2 or 3 microns
>on center.  My question is, how badly does this degrade
>our vision, allowing for all the best algorithms being
>in place to sort out the diffusion/turbidity-degraded
>image that reaches the rods & cones?
>
>John B
>

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. 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.
Interestingly, for "hyperacuity", such as vernier acuity tasks, our
capabilities go far beyond retinal or optical "resolution", down to
2-3 seconds of arc. This is accomplished by retinal processing of the
image, comparing information across receptors.


- Dick Young



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