Evolving Motor Techniques for Artificial Life Kelley Hecker, Period 7

Evolving Creatures  Creatures develop more advanced motor techniques  Progression from random movements to sophisticated patterns  Possibility of specialized creatures  Co-evolution  Both the body and the brain develop

Creature Genomes  Genome represented by a one- dimensional array  Each array has several nodes  Nodes represent body segments  Each node contains dimensions for body part, location of parent and child connections, and neuron functions  Genome converted to physical form for simulation Creature Genomes

Example Genomes  Root Node:  Length: 3, Width: 2, Height: 2  Child 0:  Length: 2, Width: 2, Height: 3  Child 1:  Length: 1, Width: 4, Height: 4  Child 2:  Length: 1, Width: 3, Height: 4  Child 3:  Length: 1, Width: 3, Height: 2 Example Genomes Note: Each node also contains the neuron data, but since this cannot be seen physically I did not list it

More Genomes

Methodology: Controller  Controller object maintains an array of genomes  Generates new genomes at beginning of simulation  Displays creatures and runs simulation  Measures fitness and breeds creatures for next generation

Methodology: Nodes  Physical dimensions  Where the body segment connects to its parent and children segments  Neuron functions  Methods to add children and connection points  Accessor methods return children, dimensions and neurons

Methodology: Creature GA  Applies neuron functions to sensor values  Possible neuron functions:  Oscillating functions: sin, cos, atan, saw- wave  Other functions: sum-threshold, sign-of, min, max, mem, log, expt, devide, interpolate, differentiate  Returns joint velocity values for the associated body segment

Circulation of Data Values received from joint-angle sensors Values sent to the GA, where they are put through node's neurons Values become effectors and modify joint velocity

Reproduction  Creatures are evaluated based on their performance in the simulation  Top fifth of genomes copied directly (asexual)‏  Remaining 4/5 of genomes are crossed over in pairs

Crossover

 Children have both physical and control traits of their parents  A portion of the limbs will be physically the same and controlled in the same way as one of the parents, while the remaining limbs will be identical to the second parent  Allows for co-evolution: both the body and brain change

Simulation Process  Population is simulated in the physical environment  All of the creatures are displayed at once  Final fitnesses are evaluated and reproduced  Repeated with next generation for n generations

Example Simulation One creature is copied directly to the second generation. Can you tell which one?

Testing  Fitness tests  Measures the success of a motor method  Progression of fitness level shows evolution of technique  Create graph of fitness level over time

4 th Quarter  Continue simulation for more than two generation  Implement mutation  Graph fitness values over time  About half the creatures are “duds.” Is there a way to fix this besides repeated generations?