Evolving Neural Network Architectures in a Computational Ecology

1. Evolving Neural Network Architectures in a Computational Ecology Larry Yaeger Professor of Informatics, Indiana University Distinguished Scientist, Apple Computer Networks and Complex Systems Indiana University 18 October 2004

2. Wiring Diagram + Learning= Brain Maps

3. Motor Cortex Map

4. Motor Cortex Homunculus

5. Plasticity in Function Orientation maps: Mriganka Sur, et al Science 1988, Nature 2000

6. Plasticity in Wiring Patterns of long-range horizontal connections in V1, normal A1, and rewired A1: Mriganka Sur, et alNature 2000

7. Wiring Diagram Matters • Relative consistency of brain maps across large populations • Lesion/aphasia studies demonstrate very specific, limited effects • Moderate stroke damage to occipital lobe can induce Charcot-Wilbrand syndrome (loss of dreams) • Scarcity of tissue in localized portion of visual system (parietooccipital/intraparietal sulcus) is method of action for gene disorder, Williams Syndrome (lack of depth perception, inability to assemble parts into wholes)

8. Monkey Cortex, Blasdel and Salama Simulated Cortex, Ralph Linsker Real & Artificial Brain Maps Distribution of orientation-selective cells in visual cortex

9. Neuronal Cooperation John Pearson, Gerald Edelman

10. Neuronal Competition John Pearson, Gerald Edelman

11. The Story So Far… • Brain maps are good • Brain maps are derived from • General purpose learning mechanism • Suitable wiring diagram • Artificial neural networks capture key features of biological neural networks using • Hebbian learning • Suitable wiring diagram

12. How to Proceed? • Design a suitable neural architecture • Simple architectures are easy, but are limited to simple (but robust) behaviors • W. Grey Walter’s Turtles • First few Valentino Braitenberg Vehicles (#1-3, of 14) • Complex architectures are much more difficult! • We know a lot about neural anatomy • There’s a lot more we don’t know • It is being tried – Steve Grand’s Lucy

13. How to Proceed? • Evolve a suitable neural architecture • It ought to work • Valentino Braitenberg’s Vehicles (#4 and higher) • We know it works • Genetic Algorithms (computational realm) • Natural Selection (biological realm)

14. Evolution is a Tautology • That which survives, persists. • That which reproduces, increases its numbers. • Things change. • Any little niche…

15. Move Turn Eat Mate Fight etc. Neural Architectures for Controlling Behavior using Vision

18. What Polyworld Is • An electronic primordial soup experiment • Why do we get science, instead of ratatouille? • Right ingredients in the right pot under the right conditions • An attempt to approach artificial intelligence the way natural intelligence emerged: • Through the evolution of nervous systems in an ecology • An opportunity to work our way up through the intelligence spectrum • Tool for evolutionary biology, behavioral ecology, cognitive science

19. What Polyworld Is Not • Fully open ended • Even natural evolution is limited by physics (and previous successes) • Accurate model of microbiology • Accurate model of any particular ecology • Though it is possible to model specific ecologies • Accurate model of any particular organism’s brain • Though many neural models are possible • A strong model of ontogeny

20. What is Mind? • Hydraulics (Descartes) • Marionettes (ancient Greeks) • Pulleys and gears (Industrial Revolution) • Telephone switchboard (1930’s) • Boolean logic (1940’s) • Digital computer (1960’s) • Hologram (1970’s) • Neural Networks (1980’s - ?) • Studying what mind is (the brain) instead of what mind is like

21. Polyworld Overview • Computational ecology • Organisms have genetic structure and evolve over time • Organisms have simulated physiologies and metabolisms • Organisms have neural network “brains” • Arbitrary, evolved neural architectures • Hebbian learning at synapses • Organisms perceive their environment through vision • Organisms’ primitive behaviors are neurally controlled • Fitness is determined by Natural Selection alone • Bootstrap “online GA” if required

23. Genetics: Physiology Genes • Size • Strength • Maximum speed • Mutation rate • Number of crossover points • Lifespan • Fraction of energy to offspring • ID (mapped to body’s green color component)

24. Genetics: Neurophysiology Genes • # of neurons for red component of vision • # of neurons for green component of vision • # of neurons for blue component of vision • # of internal neuronal groups • # of excitatory neurons per group • # of inhibitory neurons per group • Initial bias of neurons per group • Bias learning rate per group • Connection density per pair of groups & types • Topological distortion per pair of groups & types • Learning rate per pair of groups & types

25. Physiology and Metabolism • Energy is expended by behavior & neural activity • Size and strength affect behavioral energy costs(and energy costs to opponent when attacking) • Neural complexity affects mental energy costs • Size affects maximum energy capacity • Energy is replenished by eating food (or other organisms) • Health energy is distinct from Food-Value energy • Body is scaled by size and maximum speed

26. Perception: Neural System Inputs • Vision • Internal energy store • Random noise

27. Behavior: Neural System Outputs • Primitive behaviors controlled by single neuron • “Volition” is level of activation of relevant neuron • Move • Turn • Eat • Mate (mapped to body’s blue color component) • Fight (mapped to body’s red color component) • Light • Focus

28. Behavior Sample: Eating

29. Behavior Sample: Killing & Eating

30. Behavior Sample: Mating

31. Behavior Sample: Lighting

32. Neural System: Internal Units • No prescribed function • Neurons • Synaptic connections

33. Evolving Neural Architectures

34. sijt = synaptic efficacy from neuron j to neuron i at time t ait= neuronal activation of neuron i at time t ckl= learning rate for connection of type c (e-e, e-i, i-e, or i-i) from cluster l to cluster k Neural System: Learning and Dynamics • Simple summing and squashing neuron model • xi = ∑ ajt sijtj • ait+1 = 1/(1 + e-xi) • Hebbian learning • sijt+1 = sijt + ckl(ait+1 - 0.5)(ajt - 0.5)

35. Emergent Species: “Joggers”

36. Emergent Species: “Indolent Cannibals”

37. Emergent Species: “Edge-runners”

38. Emergent Species: “Dervishes”

39. Emergent Behavior: Visual Response

40. Emergent Behavior: Fleeing Attack

41. Emergent Behaviors: Foraging, Grazing, Swarming

42. A Few Observations • Evolution of higher-order, ethological-level behaviors observed • Selection for use of vision observed • This approach to evolution of neural architectures generates a broad range of network designs

43. Is It Alive? Ask Farmer & Belin… • “Life is a pattern in spacetime, rather than a specific material object.” • “Self-reproduction.” • “Information storage of a self-representation.” • “A metabolism.” • “Functional interactions with the environment.” • “Interdependence of parts.” • “Stability under perturbations.” • “The ability to evolve.”

44. Information Is What Matters • "Life is a pattern in spacetime, rather than a specific material object.” - Farmer & Belin (ALife II, 1990) • Schrödinger speaks of life being characterized by and feeding on “negative entropy” (What Is Life? 1944) • Von Neumann describes brain activity in terms of information flow (The Computer and the Brain, Silliman Lectures, 1958) • Informational functionalism • It’s the process, not the substrate • What can information theory tell us about living, intelligent processes…

45. IV Wolfram's CA classes: I = Fixed II = Periodic III = Chaotic IV = Complex II III Mutual Information I Normalized Entropy Information and Complexity • Chris Langton’s “lambda” parameter (ALife II) • Complexity = length of transients •  = # rules leading to nonquiescent state / # rules High Complexity Low 0.0 1.0 c Lambda • Crutchfield: Similar results measuring complexity of finite state machines needed to recognize binary strings

46. Quantifying Life and Intelligence • Measure state and compute complexity • What complexity? • Mutual Information • Adami’s “physical” complexity • Gell-Mann & Lloyd’s “effective” complexity • What state? • Chemical composition • Electrical charge • Aspects of behavior or structure • Neuronal states • Other issues • Scale, normalization, sparse data

47. Future Directions • Compute and record measure(s) of complexity • Use best complexity measure(s) as fitness function • More environmental interaction • Pick up and put down pieces of food • Pick up and put down pieces of barrier • More complex environment • More control over food growth patterns • Additional senses • More complex, temporal (evolved?) neural models

48. Future Directions • Behavioral Ecology benchmarks • Optimal foraging • Patch depletion (Marginal Value Theorem) • Patch selection (profitability vs. predation risk) • Vancouver whale populations • Evolutionary Biology problems • Speciation = ƒ (population isolation) • Altruism = ƒ (genetic similarity) • Classical conditioning, intelligence assessment experiments

49. Future Directions • Source code is available • Original SGI version at ftp.apple.com in /research/neural/polyworld • New Mac/Windows/X11 version coming soon, based on Qt <http://www.trolltech.com> • Paper and other materials at <http://pobox.com/~larryy>

50. Evolving Neural Network Architectures in a Computational Ecology Larry Yaeger mailto: larryy@indiana.edu http://pobox.com/~larryy Networks and Complex Systems Indiana University 18 October 2004