From: venk@stein.u.washington.edu (Venkatesh Murthy)
Newsgroups: bionet.info-theory
Subject: Re: Animate Nature and Noise (Optical Tweezers)
Keywords: references on info-theory in neural coding
Date: 28 Jan 93 23:38:18 GMT
Organization: University of Washington, Seattle
NNTP-Posting-Host: stein.u.washington.edu

In article <1k9lsvINNosr@MINERVA.CIS.YALE.EDU> smith-una@yale.edu (Una Smith) writes:
>
>Imagine the particle is a star like our sun.  Each photon wears its own
>"particle" hat, and like a spaceship using a star or planet to change
>course and gain velocity, an individual photon whips around the particle.
>The particle also changes its momentum a little bit (conservation of
>energy).  When there are lots of photons whipping around the particle's
>minute gravity well, the net momentum of the particle goes to 0, relative
>to the light stream.  Have you ever elevated a ping-pong ball by sticking
>the intake hose on a vacuum cleaner on the outtake (?) so air blows out?
>The ping-pong ball acts as though it were stuck on the end of an invisible
>wire in the airstream from the hose.  The physics are similar, except that
>the transfer of force is accomplished through friction, not gravity.  Or
>is it an atomic friction after all?  What is gravity?  What is friction?
>
>
>-- 
>
>      Una Smith      Biology Department       smith-una@yale.edu
>                     Yale University
>                     New Haven, CT  06511


OK.  I'll poke my head out a bit again.  There was a little article
by Steve Block in Nature last month about Optical Tweezers.  It appeared
as (of all things) a Product Review.  It was titled "Making light work
with optical tweezers".  Nature 360:493-495, 3 Dec 1992.  

It has a couple of nice simple figures, as well as many references.  I
gathered that simply thinking of momentum transfer may
not be enough to explain the tweezing effect.  Because a lot of the 
momentum/force due to scattering will tend to point IN the direction of the
light propogation.  Block points out that what really helps to "tweeze"
the object of interest is the GRADIENT in the light intensity.  One
way to do it is to simply focus the beam, because there is automatically
a steep gradient at the edge of the focus.  Block points out that this
"gradient force" must overcome the "traditional scattering force" in
order to hold the object from being "scattered in the direction of the 
beam".  You should really read his review - it's much better and
knowledgable than my ramblings.  One more thing though.  The person
who developed this technique first is A. Ashkin at Bell Labs.

I also wanted to list some references relating to the use of info.
theory in neural coding.  I'm only going to point out some recent
stuff.  The usage if info-theory in this field actually goes back a 
long way :-)  I also apologize for being perhaps one of the last 
hold-outs against the standard bibtex style listing...

1. Atick, J.J. Could information theory provide an ecological theory
of sensory processing? Network 3:213-251. 1992. 
	A nice review.

2. Atick, J.J. and Redlich, A.N. What does the retina know about
natural scenes? Neural Computation 4:196-210. 1992.

3. Bialek, W. et al. Reading a neural code. Science 252:1854-1857.
28 June 1991.

4. Bialek, W. and Rieke, F. Reliability and information transmission
in spiking neurons. Trends in Neurosciences 15(11);428-434.  1992.
	Review article.

5. Bialek, W. in 1989 Lectures in Complex Systems, SFI studies
in the science of complexity. E. Jen, Ed. Addison Wesley, Reading,
MA,1990. vol. 2 pp. 513-595.
	All the math you want and more...

5. Laughlin, S. The reliability of single neurons and circuit
design: a case study. Chapter 17 in "The Computing Neuron", Eds:
R. Durbin, C. Miall and G. Mitchison. (sorry, my copy doesn't 
have the publisher's name!).
	If you can't find this, check out any other paper by
	Simon Laughlin.  He works on fly vision.



Now everyone can go read these for this week's assignment and prepare
a report due next week :-) :-) :-)

-Venki Murthy
Physiology & Biophysics
Univ. of Washington
Seattle, WA 98195.
(venk@u.washington.edu)