[Neuroscience] What causes the characteristic curve of photoreceptors?

Marc Wossner via neur-sci%40net.bio.net (by marc.wossner from gmx.net)
Tue Jan 8 18:46:56 EST 2008

dear ng,

can someone help me with the following: What is the characteristic
curve of our rod and cone photoreceptors determined by? I found some
plots of in vivo measurings of cone receptor potentials that show a
clear s-form (http://www.handprint.com/HP/WCL/color4.html#lightadapt,
scroll down a bit). That is a kind of toe in the lower part, a linear
section in the middle and a kind of shoulder in the upper part. So
luminance differences are compressed in the toe and in the shoulder
but rendered 1:1 in the middle. Is this caused by a kind of nonlinear
response to light alone or do other neurophysiological mechanisms,
like lateral inhibition, play a role as well?

Many thanks for your input!

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