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Philosophers

Mortimer Adler
Rogers Albritton
Alexander of Aphrodisias
Samuel Alexander
William Alston
Anaximander
G.E.M.Anscombe
Anselm
Louise Antony
Thomas Aquinas
Aristotle
David Armstrong
Harald Atmanspacher
Robert Audi
Augustine
J.L.Austin
A.J.Ayer
Alexander Bain
Mark Balaguer
Jeffrey Barrett
William Belsham
Henri Bergson
George Berkeley
Isaiah Berlin
Richard J. Bernstein
Bernard Berofsky
Robert Bishop
Max Black
Susanne Bobzien
Emil du Bois-Reymond
Hilary Bok
Laurence BonJour
George Boole
Émile Boutroux
F.H.Bradley
C.D.Broad
Michael Burke
C.A.Campbell
Joseph Keim Campbell
Rudolf Carnap
Carneades
Ernst Cassirer
David Chalmers
Roderick Chisholm
Chrysippus
Cicero
Randolph Clarke
Samuel Clarke
Anthony Collins
Antonella Corradini
Diodorus Cronus
Jonathan Dancy
Donald Davidson
Mario De Caro
Democritus
Daniel Dennett
Jacques Derrida
René Descartes
Richard Double
Fred Dretske
John Dupré
John Earman
Laura Waddell Ekstrom
Epictetus
Epicurus
Herbert Feigl
John Martin Fischer
Owen Flanagan
Luciano Floridi
Philippa Foot
Alfred Fouilleé
Harry Frankfurt
Richard L. Franklin
Michael Frede
Gottlob Frege
Peter Geach
Edmund Gettier
Carl Ginet
Alvin Goldman
Gorgias
Nicholas St. John Green
H.Paul Grice
Ian Hacking
Ishtiyaque Haji
Stuart Hampshire
W.F.R.Hardie
Sam Harris
William Hasker
R.M.Hare
Georg W.F. Hegel
Martin Heidegger
Heraclitus
R.E.Hobart
Thomas Hobbes
David Hodgson
Shadsworth Hodgson
Baron d'Holbach
Ted Honderich
Pamela Huby
David Hume
Ferenc Huoranszki
William James
Lord Kames
Robert Kane
Immanuel Kant
Tomis Kapitan
Jaegwon Kim
William King
Hilary Kornblith
Christine Korsgaard
Saul Kripke
Andrea Lavazza
Keith Lehrer
Gottfried Leibniz
Leucippus
Michael Levin
George Henry Lewes
C.I.Lewis
David Lewis
Peter Lipton
C. Lloyd Morgan
John Locke
Michael Lockwood
E. Jonathan Lowe
John R. Lucas
Lucretius
Alasdair MacIntyre
Ruth Barcan Marcus
James Martineau
Storrs McCall
Hugh McCann
Colin McGinn
Michael McKenna
Brian McLaughlin
John McTaggart
Paul E. Meehl
Uwe Meixner
Alfred Mele
Trenton Merricks
John Stuart Mill
Dickinson Miller
G.E.Moore
Thomas Nagel
Friedrich Nietzsche
John Norton
P.H.Nowell-Smith
Robert Nozick
William of Ockham
Timothy O'Connor
Parmenides
David F. Pears
Charles Sanders Peirce
Derk Pereboom
Steven Pinker
Plato
Karl Popper
Porphyry
Huw Price
H.A.Prichard
Protagoras
Hilary Putnam
Willard van Orman Quine
Frank Ramsey
Ayn Rand
Michael Rea
Thomas Reid
Charles Renouvier
Nicholas Rescher
C.W.Rietdijk
Richard Rorty
Josiah Royce
Bertrand Russell
Paul Russell
Gilbert Ryle
Jean-Paul Sartre
Kenneth Sayre
T.M.Scanlon
Moritz Schlick
Arthur Schopenhauer
John Searle
Wilfrid Sellars
Alan Sidelle
Ted Sider
Henry Sidgwick
Walter Sinnott-Armstrong
J.J.C.Smart
Saul Smilansky
Michael Smith
Baruch Spinoza
L. Susan Stebbing
Isabelle Stengers
George F. Stout
Galen Strawson
Peter Strawson
Eleonore Stump
Francisco Suárez
Richard Taylor
Kevin Timpe
Mark Twain
Peter Unger
Peter van Inwagen
Manuel Vargas
John Venn
Kadri Vihvelin
Voltaire
G.H. von Wright
David Foster Wallace
R. Jay Wallace
W.G.Ward
Ted Warfield
Roy Weatherford
William Whewell
Alfred North Whitehead
David Widerker
David Wiggins
Bernard Williams
Timothy Williamson
Ludwig Wittgenstein
Susan Wolf

Scientists

Michael Arbib
Bernard Baars
Gregory Bateson
John S. Bell
Charles Bennett
Ludwig von Bertalanffy
Susan Blackmore
Margaret Boden
David Bohm
Niels Bohr
Ludwig Boltzmann
Emile Borel
Max Born
Satyendra Nath Bose
Walther Bothe
Hans Briegel
Leon Brillouin
Stephen Brush
Henry Thomas Buckle
S. H. Burbury
Donald Campbell
Anthony Cashmore
Eric Chaisson
Jean-Pierre Changeux
Arthur Holly Compton
John Conway
John Cramer
E. P. Culverwell
Charles Darwin
Terrence Deacon
Louis de Broglie
Max Delbrück
Abraham de Moivre
Paul Dirac
Hans Driesch
John Eccles
Arthur Stanley Eddington
Paul Ehrenfest
Albert Einstein
Hugh Everett, III
Franz Exner
Richard Feynman
R. A. Fisher
Joseph Fourier
Lila Gatlin
Michael Gazzaniga
GianCarlo Ghirardi
J. Willard Gibbs
Nicolas Gisin
Paul Glimcher
Thomas Gold
A.O.Gomes
Brian Goodwin
Joshua Greene
Jacques Hadamard
Patrick Haggard
Stuart Hameroff
Augustin Hamon
Sam Harris
Hyman Hartman
John-Dylan Haynes
Martin Heisenberg
Werner Heisenberg
John Herschel
Jesper Hoffmeyer
E. T. Jaynes
William Stanley Jevons
Roman Jakobson
Pascual Jordan
Ruth E. Kastner
Stuart Kauffman
Simon Kochen
Stephen Kosslyn
Ladislav Kovàč
Rolf Landauer
Alfred Landé
Pierre-Simon Laplace
David Layzer
Benjamin Libet
Seth Lloyd
Hendrik Lorentz
Josef Loschmidt
Ernst Mach
Donald MacKay
Henry Margenau
James Clerk Maxwell
Ernst Mayr
Ulrich Mohrhoff
Jacques Monod
Emmy Noether
Howard Pattee
Wolfgang Pauli
Massimo Pauri
Roger Penrose
Steven Pinker
Colin Pittendrigh
Max Planck
Susan Pockett
Henri Poincaré
Daniel Pollen
Ilya Prigogine
Hans Primas
Adolphe Quételet
Juan Roederer
Jerome Rothstein
David Ruelle
Erwin Schrödinger
Aaron Schurger
Claude Shannon
David Shiang
Herbert Simon
Dean Keith Simonton
B. F. Skinner
Roger Sperry
Henry Stapp
Tom Stonier
Antoine Suarez
Leo Szilard
William Thomson (Kelvin)
Peter Tse
Heinz von Foerster
John von Neumann
John B. Watson
Daniel Wegner
Steven Weinberg
Paul A. Weiss
John Wheeler
Wilhelm Wien
Norbert Wiener
Eugene Wigner
E. O. Wilson
H. Dieter Zeh
Ernst Zermelo
Wojciech Zurek

Presentations

Biosemiotics
Free Will
Mental Causation
James Symposium
 
Paul Glimcher

Paul Glimcher is a neuroscientist and behavioral psychologist who founded the new field of neuroeconomics.

Glimcher has been unusual among scientists to take seriously the significance of quantum indeterminacy in the biological sciences. Since Galileo, Kepler, and Newton, the paradigm of quantitative and mathematical science has been predictability. This in turn depends above all on causal laws, which appeared to most thinkers to require determinism. Reductionists argue that biology is reducible to physics and chemistry and thus subject to the same causal laws.

We now know that determinism is an emergent phenomenon, not yet present when the universe consisted of only radiation and a few elementary particles for the first few hundred thousand years.

Macroscopic bodies like the planets are aggregates of vast numbers of particles that average over the microscopic quantum uncertainty. Their behavior is the statistical consequence of the law of large numbers. It was macroscopic bodies, especially planets, but also billiard balls, that gave us Newton's laws, driving our intuition that everything must follow such "universal" laws.

Glimcher makes the case that human and animal behavior, dependent ultimately on very small brain structures that approach the quantum level, may involve the irreducible indeterminacy of quantum mechanics and challenge the standard assumptions of behavioral science.

Since René Descartes, the bodies of humans and animals have been assumed to be machines following deterministic and causal laws. Descartes drew diagrams of the reflex arc of afferent signals from a foot feeling pain, up to the brain, and efferent signals back down to pull the muscles away. (Descartes located freedom of the will in the separate substance of a human mind. Animals lacked such freedom.)

This reflex arc of causes and effects, and the related metaphor of biological processes as "mechanisms," prominent in the great twentieth century work of Charles Sherrington, is still the most common textbook explanation today.

Glimcher is surprised to find that the great Erwin Schrödinger, one of the founders of quantum mechanics, argued in his influential 1944 essay, "What Is Life," that indeterminacy could play no role. This essay had an enormous but unfortunate impact on the development of biology, especially on the work of Max Delbrück and other molecular biologists.

Glimcher writes:

[Schrödinger] argued that fundamental indeterminacy would never arise in the living world because if it were not so, if we were organisms so sensitive that a single atom, or even a few atoms, could make a perceptible impression on our senses
Heavens, what would life be like! To stress one point: an organism of that kind would most certainly not be capable of developing the kind of orderly thought which, after passing through a long sequence of earlier stages, ultimately results in forming, among many other ideas, the idea of an atom. (Schrodinger 1944)
Our existing data, although ambiguous, clearly challenge Schrodinger’s conclusion. The vertebrate nervous system is sensitive to the actions of single quantum particles. At the lowest levels of perceptual threshold, the quantum dynamics of photons, more than anything else, governs whether or not a human observer sees a light. Synapses and neurotransmission also seem to violate this assumption of Schrodinger’s, and these are the building blocks from which neurocomputation is achieved. In the end, Schrodinger may be right, behavior may be fundamentally determinate, but it would be premature to draw that conclusion now. Behavioral scientists will have to continue to explore apparent indeterminacy in behavior and will have to develop the methodological tools for determining whether this apparent indeterminacy is fundamental.
Glimcher may be unaware of the deep philosophical reasons that led Schrödinger away from his early commitment to statistical views of physics (under the influence of his teacher Franz Exner and Ludwig Boltzmann). Schrödinger later became a hardened determinist along with Albert Einstein, Louis deBroglie, David Bohm, and others who challenged the indeterminacy of quantum physics to the ends of their lives.

After reviewing the research into stochastic behavior in neuron production of action potentials, Glimcher summarizes the likelihood that this indeterminacy might rise to the level of behavior.

The evidence that we have today suggests that membrane voltage can be influenced by quantum level events, like the random movement of individual calcium ions. So there is every reason to believe that membrane voltage can be viewed, at least under some circumstances, as a formally indeterminate process of the type that precludes Popperian falsifiability. How does this membrane voltage influence action potential generation? Recall that cells receive a mixture of excitation and inhibition from thousands of synapses and that the ratio of this mixture is variable. Imagine that the correlations between the activity of the individual synapses impinging on a given cell were variable. Under conditions in which the activity of many synapses is correlated and the membrane voltage is driven either way above or way below its threshold for action potential generation, the network of neurons itself would maintain a largely determinate characteristic even though the synapses themselves might appear stochastic. Alternatively, when the synaptic activity is uncorrelated and the forces of excitation and inhibition are balanced, small uncorrelated fluctuations in synaptic probabilities drive cells above or below threshold. Under these conditions, indeterminacy in the synapses propagates to the membrane voltage and thence to the pattern of action potential generation. Indeterminacy in the pattern of action potential generation, although variable, would reflect a fundamental indeterminacy in the nervous system.

At the level of behavior, apparent indeterminacy is reinforced by the environment and has been observed. Animals can produce behavior that appears to scientists to be indeterminate. How does this apparent indeterminacy arise? Given what we know about the behavior of synapses and action potentials, two possibilities present themselves. The fundamental indeterminacy observed at the cellular level could be prevented from influencing higher-level phenomena in the nervous system, rendering these higher-level phenomena determinate. These determinate processes could then instantiate pseudorandom computations that emulate the underlying cellular indeterminacy and yield apparently indeterminate behavior. Alternatively, we can propose the hypothesis that indeterminacy observed at the cellular level could propagate to behavior under some circumstances, yielding truly indeterminate behavior under some conditions and more determinate behaviors under others.

The leading German neurogeneticist Martin Heisenberg has shown stochastic behavior in fruit flies and probably even bacteria, arguing that humans and animals are therefore not determined beings. We argue further that human behavior can be adequately determined and that indeterminacy provides the generator of alternative possibilities that makes us creative and the authors of our own lives.
We are not pre-determined, as many scientists and philosophers may still believe.
For Teachers
For Scholars
Among the first scientists to examine the pattern of cortical neuronal firing rates with regard to indeterminacy were Tolhurst et al. (1981) and Dean (1981), who were extending studies of neuronal variability pioneered by Barlow & Levick (1969; see also Heggelund & Albus 1978). In two landmark papers, Tolhurst et al. (1981) and Dean (1981) examined the firing patterns of neurons in the visual cortices of anesthetized cats viewing visual displays that presented moving bars of light.

What Tolhurst et al. (1981) and Dean (1981) found, therefore, was that at the level of action potential generation, cortical neurons could be described as essentially stochastic. This was a surprising result at the time, and it has been widely confirmed (Rieke et al. 1997, Shadlen & Newsome 1998). What then is the source of this apparent stochasticity, and would a more detailed biophysical analysis of the spike generation mechanism reveal an underlying deterministic process that would yield this apparent indeterminacy?

To examine one possible answer to that question, Mainen & Sejnowski (1995) sought to determine whether the biophysical process that actually generates action potentials in response to changes in membrane voltage was determinate...

They found that the spike-generating mechanism was fully deterministic. A given pattern of membrane voltage gave rise to exactly the same pattern of action potentials no matter how many times it was injected into the cell.

On the one hand, this was a reassuring result. At base, the pattern of action potential generation was found to be governed by a determinate device. However, on the other hand, it was puzzling. Spike rates are not determinate in this sense. Tolhurst et al. and Dean’s work indicates that spike rates are distributed in a Poisson-like fashion, and there clearly is nothing about the spike generator within each cell that produces this pattern. The Mainen & Sejnowski (1995) data indicate that the apparent randomness in spike patterns must be a function of apparent randomness in the underlying membrane voltages. What then are the sources of these Poisson-like fluctuations in membrane voltage?

We know that membrane voltages are governed, ultimately, by the pattern of synaptic activations that a cell receives from the neurons that impinge upon it. Each cortical neuron receives about 10,000 synapses from the tissue that surrounds it. The fact that about half of these synapses are excitatory and half are inhibitory is also important. It means that net excitation and inhibition are largely balanced in an active neuron and small shifts in this balance cause the membrane voltage to rise and fall, and thus cause action potentials to be generated. Together, these observations make a clear suggestion. The source of the apparent stochasticity in the membrane voltage either is a determinate pattern of synaptic activations that carefully sculpts the membrane voltage to yield an apparently indeterminate pattern of action potentials for reasons we do not yet understand or the process of synaptic activation is itself apparently indeterminate.

A number of groups have investigated this latter possibility by studying the activity of single synapses (see Auger & Marty 2000, Stevens 2003 for reviews of this literature). The basic approach taken by these groups has been to activate a neuron and then monitor the rate at which individual synaptic vesicles are released into the synaptic cleft. Before these experiments were undertaken one could have speculated that synapses were simple determinate mechanisms: When an action potential invades the presynaptic region, it might be presumed that synaptic vesicles of neurotransmitter were deterministically released into the synaptic cleft. Modern studies of this process seem to contradict this view, however. Current evidence indicates that when an action potential invades the presynaptic terminal, the chance that a single synaptic vesicle will be released can be as low as 20%. Examinations of the precise patterns of vesicular release suggest that the likelihood that a vesicle of neurotransmitter will be released in response to a single action potential can be described as a random Poisson-like process. Vesicular release seems to be an apparently indeterminate process.

Careful study of other elements in the synapse seems to yield a set of similar, and highly stochastic, results. Postsynaptic membranes, for example, seem to possess only a tiny number of neurotransmitter receptors (cf. Takumi et al. 1999), and during synaptic transmission as few as one or two of a given type of receptor molecules may be activated (Nimchinski et al. 2004). Under these conditions, a single open ion channel may allow a countable number of calcium or sodium ions to enter the neuron, and there is evidence that the actions of a single receptor and the few ions that it channels into the cell may influence the postsynaptic membrane. Together, all of these data suggest that membrane voltage is the product of interactions at the atomic level, many of which are governed by quantum physics and thus are truly indeterminate events. Because of the tiny scale at which these processes operate, interactions between action potentials and transmitter release as well as interactions between transmitter molecules and postsynaptic receptors may be, and indeed seem likely to be, fundamentally indeterminate.

In 1944, Schrodinger argued that the fundamental indeterminacy of the physical universe would have no effect on living systems. He argued that were biological systems to become so small that the actions of single atoms or molecules could influence cells, the resulting organisms would surely perish from the evolutionary landscape. Studies of the mammalian synapse, however, seem to indicate that Schrodinger (1944) was simply wrong in this regard. Single synapses appear to be indeterminate devices; not apparently indeterminate, but fundamentally indeterminate. At base, physical indeterminacy seems to be a fundamental property of the brain. But how sure can we be that this fundamental indeterminacy at the level of the synapse has anything to do with indeterminacy at the level of a single cortical neuron, at the level of a cortical network, at the level of behavior, or at the level of a social theory of behavior?

The evidence that we have today suggests that membrane voltage can be influenced by quantum level events, like the random movement of individual calcium ions. So there is every reason to believe that membrane voltage can be viewed, at least under some circumstances, as a formally indeterminate process of the type that precludes Popperian falsifiability. How does this membrane voltage influence action potential generation? Recall that cells receive a mixture of excitation and inhibition from thousands of synapses and that the ratio of this mixture is variable. Imagine that the correlations between the activity of the individual synapses impinging on a given cell were variable. Under conditions in which the activity of many synapses is correlated and the membrane voltage is driven either way above or way below its threshold for action potential generation, the network of neurons itself would maintain a largely determinate characteristic even though the synapses themselves might appear stochastic. Alternatively, when the synaptic activity is uncorrelated and the forces of excitation and inhibition are balanced, small uncorrelated fluctuations in synaptic probabilities drive cells above or below threshold. Under these conditions, indeterminacy in the synapses propagates to the membrane voltage and thence to the pattern of action potential generation. Indeterminacy in the pattern of action potential generation, although variable, would reflect a fundamental indeterminacy in the nervous system.

At the level of behavior, apparent indeterminacy is reinforced by the environment and has been observed. Animals can produce behavior that appears to scientists to be indeterminate. How does this apparent indeterminacy arise? Given what we know about the behavior of synapses and action potentials, two possibilities present themselves. The fundamental indeterminacy observed at the cellular level could be prevented from influencing higher-level phenomena in the nervous system, rendering these higher-level phenomena determinate. These determinate processes could then instantiate pseudorandom computations that emulate the underlying cellular indeterminacy and yield apparently indeterminate behavior. Alternatively, we can propose the hypothesis that indeterminacy observed at the cellular level could propagate to behavior under some circumstances, yielding truly indeterminate behavior under some conditions and more determinate behaviors under others.


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