Rune wrote:
> A lot of 
> preprocessing is done in the eyes themselves before the visual data is sent 
> to the brain.

You'd be amazed. :-)

> For example, the eyes have an edge detecting layer I think, or something 
> along those lines.

First a change detector layer, then from that a bunch of edge detectors, 
then object detectors, then motion detection, then ...

Before it leaves you're eyes, they already know there's something large 
coming towards you from the left. That info is hooked directly from eyes 
to neck muscles.

> This layer could find all the edges of the bars in your 
> image and send information about these edges on to the brain, so that the 
> brain can tell how many bars there are. 

True.

> The eyes also send the actual "raw" 
> brightness info on to the brain, but this may be in a "low resolution" where 
> no more than 16 different shades can be told apart. 

Well, it's an analog pulse train. Actually, I'm not sure how far up the 
pile before *you* decide it's no longer eyes and has become brain. I'm 
also not sure if the cells that actually sense light are integrated into 
anything at a higher level at all, or whether all their info is 
processed before getting to the "brain" part.

> However, the brain can 
> still count all the bars, becuase of the edges detected in the eyes.

> I'm not saying it's like that; just that your image doesn't prove anything 
> about the amount of gray scales the brain can tell apart. So it really comes 
> down to what you mean by "human visual system" - the eyes or the brain.

I think if you're picking out a monitor, you're worried about your 
brain's perception of it. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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