Tag Archives: neuroscience

John Doyle on handwaving and universal laws

John Doyle gave this year’s J. Barkley Rosser Lecture at the Wisconsin Institute for Discovery; his talk was dedicated to the proposition that tradeoffs between flexibility and robustness in control systems with significant delays are in the end going to be bound by universal laws, just as the operation of a classical Turing machine is bound by laws coming from information theory and complexity theory.  (A simple such one:  a machine that has the potential to produce N different outputs is going to have a worst-case run time of at least log N steps.)

Doyle believes the robustness-flexibility tradeoff should be fundamental to our way of thinking of both biological and technological devices.  He gave the following very illustrative example, which is so simple that you can play along as you read my blog.

Hold your hand in front of your face and wave your hand vigorously back and forth.  It looks blurry, right?

Now hold your hand still and shake your head equally vigorously.  No blurring!

Which is strange, because the optical problem is in some sense exactly the same.  But the mechanism is different, and so the delay time is different.  When your hand moves, you’re using the same general-function apparatus you use to track moving objects more generally.  It’s a pretty good apparatus!  But because it’s so flexible, working well for all kinds of optical challenges, it is slow, and like any system with a long delay, input that oscillates pretty fast — like your waving hand — can cross it up.

When your head moves, it’s a different story:  we have a vestibulo-ocular reflex which moves our eyes in sync with our head to fix the images on our retina in place.  This doesn’t pass through cognition at all — it’s a direct neural connection from the vestibular sensors in the inner ear to the muscles that control eye movement.  This system isn’t flexible or adaptable at all.  It does just one thing — but it does it fast.

(All this material derived from my notes on Doyle’s talk, which went pretty fast:  all mistakes are mine.)

Here are the slides from Doyle’s talk.  (TooManySlides.pdf is the best filename ever!)

Here’s a paper from Science that Doyle said would be especially useful for mathematicians who want to see how the tradeoffs in question can be precisely formalize.  (Authors:  Chandra, Buzi, Doyle.)

Tagged , , , , ,

MALBEC seminar: David Balduzzi, “Measuring consciousness as integrated information”

The new MALBEC seminar starts tomorrow!  Announcement below.

The Department of Mathematics is pleased to announce a special lecture series for Spring 2009.  The MALBEC lectures (“Mathematics, Algorithms, Learning, Brains, Engineering, Computers”) aims to encourage closer ties between mathematicians and scientists around UW doing mathematical work on the foundations of learning, perception, and behavior of people and machines. Please come, participate, and hang around afterwards with the speakers!

Up-to-date information about the series can always be found at the MALBEC home page.

Our first lecture, “Measuring consciousness as integrated information,” by David Balduzzi, will be held tomorrow, Wednesday, March 4, at 4pm, in Van Vleck B102. David holds a 2006 Ph.D. in mathematics from the University of Chicago and is now a postdoc at the UW Center for Sleep and Consciousness.  The lecture will be followed by a reception in the Van Vleck 9th floor lounge.  Upcoming speakers include Partha Niyogi (U Chicago, CS) on April 17; Michael Coen (UW, biostat and CS) on April 21; and Jerry Zhu (UW, CS) on May 6.

We are very grateful to the Wisconsin Institutes for Discovery and the Morgridge Institute for Research for their support of the MALBEC seminar.

Abstract: The integrated information theory (Tononi 2004) starts from phenomenology and makes use of thought experiments to claim that consciousness is integrated information. First: the quantity of consciousness corresponds to the amount of integrated information generated by a system of elements. Information is quantified by taking the current state as a measurement the system performs on itself, which specifies a repertoire of prior states that cause (lead to) the current state. Integrated information (phi) is quantified by computing the repertoire specified by the system as a whole relative to the repertoires specified independently by its parts. Second: the quality of an experience is completely specified by the set of informational relationships generated within that system. The set of all repertoires generated by subsystems of a system is represented in a geometric object, the quale. Informational relationships between points in the quale characterize how the measurements resulting from interactions in the system give structure to a particular experience.

After describing the theory in some detail, I will discuss how several neurobiological observations fall naturally into place in the framework: the association of consciousness with certain neural systems rather than with others; the fact that neural processes underlying consciousness can influence or be influenced by neural processes that remain unconscious; and the reduction of consciousness during dreamless sleep and generalized seizures. Furthermore, features of the quale can be related to features of conscious experience, such as modalities and submodalities, and can explain the distinct roles of different cortical subsystems in affecting the quality of experience.

Tagged , , , , , , ,
%d bloggers like this: