On Mon, 22 Oct 2007, Charles Henry wrote:
Vision doesn't work exactly like a camera.
Right. Somehow I confused two things. A maximum frequency is only called
Nyquist if it involves sampling and aliasing. There are several maximum
frequencies that can be computed for the eye for different circumstances,
which are in the range of 10 Hz up to less than 100 Hz, but those are due
to low-pass effects.
There's no sampling that occurs--the visual signals are more/less
continuous except for momentary "refresh" periods brought about by eye
motion and nystagmus. I thought about it today, and I'm not entirely
sure why it happens (perhaps there is a certain maximum speed which can
be perceived--this is equivalent to saying there is a finite bandwidth
of motion perception).
Imho this is because we are trained to see "continuous" (slow enough)
motion as continuous and sudden motion as sudden. If a change is
sufficiently startling, it makes vision snappier. Sudden motion of the eye
causes sudden motion of the scenery relative to vision, so it has an
effect similar to sudden motion of physical objects themselves.
It would explain why fast-blinking lights are considered to be straining
the eye: the eye (or vision system) makes extra effort as a response to
high activity in eye cells due to blinking, even as one wants to ignore
the blinking.
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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada
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