Reductive and Representational Explanation in Synthetic Neuroethology
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Transcript of Reductive and Representational Explanation in Synthetic Neuroethology
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Reductive and Representational Explanation in Synthetic NeuroethologyPete MandikAssistant Professor of PhilosophyCoordinator, Cognitive Science LaboratoryWilliam Paterson University, New Jersey
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Collaborators
Michael Collins, City University of New York Graduate Center
Alex Vereschagin, William Paterson University
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My Thesis
Even for the simplest cases of intelligent behavior, the best explanations are both reductive and representational
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Overview
■ Mental representation in folk-psychological explanation
■ Mental representation in non-humans
■ The problem of chemotaxis■ Modeling the neural control of
chemotaxis■ What the representations are
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Mental reps in folk-psychGeorge is opening the fridge because:George desires that he drinks some beerGeorge sees that the fridge is in front of himGeorge remembers that he put some beer in the fridge
■George’s psychological states cause his behavior■George’s psychological states have representational content
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Mental reps in non-human animalsRats and maze learningAfter finding the platform the first time, rats remember its location and can swim straight to it on subsequent trial from novel starting positions.Rats not only represent the location, but compute the shortest path.
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Mental reps in non-human animalsDucks’ representation of rate of return
Every day two naturalists go out to a pond where some ducks are overwintering and station themselves about 30 yards apart. Each carries a sack of bread chunks. Each day a randomly chosen one of the naturalists throws a chunk every 5 seconds; the other throws every 10 seconds. After a few days experience with this drill, the ducks divide themselves in proportion to the throwing rates; within 1 minute after the onset of throwing, there are twice as many ducks in front of the naturalist that throws at twice the rate of the other. One day, however, the slower thrower throws chunks twice as big. At first the ducks distribute themselves two to one in favor of the faster thrower, but within 5 minutes they are divided fifty-fifty between the two “foraging patches.” … Ducks and other foraging animals can represent rates of return, the number of items per unit time multiplied by the average size of an item.
(Gallistel 1990; emphasis mine)
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Positive Chemotaxis
Movement toward the source of a chemical stimulus
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2-D food finding
Sensors
Brain
Steering Muscles
2-Sensor Chemophile:
■ Steering muscles orient creature toward stimulus
■ Perception of stimulus being to the right fully determined by differential sensor activity
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1-D food finding
Sensor
Brain
Steering Muscles
1- Sensor “Lost” Creature
■ left/right stimulus location underdetermined by sensor activity
■ only proximity perceived
■ Adding memory can help
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Things to Note:
Note that single-sensor gradient navigation is a “representation hungry” problem
Note the folk-psychological explanation of how a human would solve the problem
Note, in what follows, the resemblance to the explanation of the worm’s solution
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C. Elegans
Caenorhabditis Elegans
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C. Elegans
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C. Elegans
Feree and Lockery (1999). “Computational Rules for Chemotaxis in the Nematode C. Elegans.” Journal of Computational Neuroscience 6, 263-277
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C. Elegans
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C. Elegans
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C. Elegans
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The Extracted Rule:
,)(2
2
210 dt
Cdz
dt
dCztCz
dt
dbias
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Zeroth Order
The simulations were run keeping only the terms up to the zeroth order:
This rule failed to produce chemotaxis for any initial position.
)(0 tCzdt
dbias
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First Order
Next the simulations were run keeping all terms up to the first order:
This rule accurately reproduced the successful chemotaxis performed by the network model.
dt
dCztCz
dt
dbias 10 )(
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Problems
Remains open. . .How the network controllers are
workingWhat the networks themselves are
representing and computingWhether the networks are utilizing
memory
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Framsticks
3-D Artificial Life simulator
By Maciej Komosinski
and Szymon Ulatowski Poznan University of Technology, Poland
http://www.frams.poznan.pl/
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Framsticks
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Framsticks nematodes
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Memory in Chemotaxis
■ Experimental Set Up◆ 3 orientation networks: Feed-
forward, Recurrent, and Blind◆ five runs each, for 240 million steps◆ mutations allowed only for neural
weights◆ fitness defined as lifetime distance◆ Initial weights: Evolved CPGs with
un-evolved (zero weights) orienting networks
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1 2 3 4 5 6 7 8 9 10 11 12
Series1
Series2
Series3
Results
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What the representations are
States of neural activation isomorphic to and causally correlated with environmental states
■ Sensory states■ Memory states■ Motor-command states
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Representation and IsomorphismIsomorphism
One to one mapping between structures structure = set of
elements plus set of relations on those elements
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Representation and IsomorphismRepresentation
Primarily: a relation between isomorphic structures
Secondarily: a relation between elements and/or relations in one structure and those in another
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Isomorphisms between multiple structuresWhich of the many structures a given
structure is isomorphic to, does a given structure represent?
The range of choices will be narrowed by the causal networks the structure is embedded in
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For further investigation
■ States of desire/motivation◆ Clearer in models of action selection,
not intrinsic to the stimulus orientation networks
■ Modeling representational error and falsity◆ Error and falsity are distinct, but this
is clearer in non assertoric attitudes
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Summing up
Single-sensor chemotaxis is a “representation hungry” problem
Even explanations of adaptive behaviors as simple as chemotaxis benefit from psychological state ascriptions
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Summing up
The psychological states in question are identical to neural states
The neural states in question are causally explanatory of intelligent behavior in virtue of isomorphisms between structures of neural activations and structures of environmental features
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Summing up
Therefore…
Even for the simplest cases of intelligent behavior, the best explanations are both reductive and representational
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THE END