[PD] Spectrum graphing amplitude problem

[Mathieu Bouchard]

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