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Linearly encoded information in the brain

mark r meiss mmeiss at avocado.ucs.indiana.edu
Wed Jul 12 13:20:04 EST 1995

Greetings.  I am currently working in modeling part of the visual system 
with artificial neural networks.  In the area with which I am working, 
there are neurons that linearly encode eye position--that is, the firing 
rate of the neuron increases linearly with position in degrees.  These 
are input neurons.  When I examine the emergent behavior of the hidden 
neurons in the networks that I train, I find a multiplicative effect of 
this linear input on the hidden neuron activity; this phenomenon has been 
referred to as a "gain field".  The pattern of response of a hidden unit 
might be one value at eye position (-10,-10) and another value at eye 
position (10,10).  The shape of this gain field is planar.

My research suggests that the appearance of this gain field is not due to 
either the learning rule used (I have utilized both propagation and a 
genetic selection algorithm) or the function of the network, but rather 
due to the linearity of the input data.  I would like to determine 
whether this behavior is a trait of just ANN's or information in general 
(and thus of the brain as well).

So, my question is, what other areas of the brain involve linearly 
encoded inputs?  I know that linear inputs in the brain are fairly rare, 
but there must be others.  Furthermore, has anyone familiar with these 
other areas of the brain observed a similar "gain field" effect?

Any advice or pointers to the appropriate literature would be greatly 

Mark Meiss
Indiana University CS Dept.

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