How the retina works

Scott Seidman namdiesttocs at mindspring.com
Fri Jul 2 15:53:15 EST 2004


"Wil Hadden" <ask at me.com> wrote in news:2klmr3F42gqoU1 at uni-berlin.de:

> 
> "Scott Seidman" <namdiesttocs at mindspring.com> wrote in message >
>> FWIW, I'm not sure you need to go into each layer, so much as the
>> effective output of the ganglion cells and center-surround
>> antagonism. It depends on why you want to model the retina in the
>> first place. 
>>
>>  Even more pertinent to your work might be Marr, "Vision", Freeman,
>>  1982. 
>> In all your searches, add the phrase "lateral inhibition"-- its my
>> favorite network architecture.  It retina, it serves as a spatial
>> differentiator, but in brainstem and spinal cord is serves a temporal
>> integrator.  Lateral inhibition-- is there anything it can't do?
>>
>> Scott
> 
> Lateral inhibition looks promising I must say. It resembles a self
> organising map in neural networks and seems to be very useful!
> I'm presuming that the horizontal and amacrine cells exhibit lateral
> inhibition, so there's no getting away from it!
> 
> Wil
> 
> 
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Lateral inhibition is the mechanism for the whole center-surround 
antagonism operation of the retina.  If you think about it, it not only 
enhances edge detection, it increases the dynamic range of the entire 
retina.  The horizontal cells implement lateral inhibition at the 
photoreceptor level, and the amacrine cells at the ganglion cell level.  
The bipolar cells essentially define whether a ganglion cell is on-
center/off-surround, or off-center/on-surround.

An interesting tidbit-- the light has to pass through the ganglion, 
bipolar, amacrine, and horizontal cells, as well as the cell body of the 
photoreceptors, before hitting the light sensitive parts of the 
photoreceptor.  At the fovea, this isn't as true-- the upper layers are 
sort of pushed aside

Scott



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