Alan Saul saul+ at pitt.edu
Tue Sep 20 00:08:44 EST 1994

In article <35l0hc$93p at eldborg.rhi.hi.is>, thoreys at rhi.hi.is (Thor
Eysteinsson) wrote:

> In <35kksg$2sr at portal.gmu.edu> herwin at mason1.gmu.edu (HARRY R. ERWIN) writes:
> >Has anyone studied how the brain does the log transformation involved in 
> >scaling sensory input and adapting to the background level?
> That is a big question, a lot of work there. A great deal of the "scaling"
> takes place at the receptor level, as well as adaptation. 

> This has also been examined at the level of the thalamus, but LGN neurons do
> not respond that much differently than retinal ganglion cells

Not true, but beside the point here.
Cortical neurons all adapt, and do so in quite interesting ways. I doubt
that you could seriously model what happens as a log transform.
Aftereffects are specific to the adapting stimulus, implying that inputs to
the cell being examined are involved in the process. One guess is that
active inhibitory inputs are potentiated by adapting, although there is
little evidence that supports this hypothesis, unfortunately. However, it
works well in principle. The field is quite active on both experimental and
theoretical fronts. If you want references email me (or just do a search!).
Alan Saul
saul+ at pitt.edu

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