Inputs?? What input do you use to tell the arm to move up? Down? Move fast? Hold still? Encoding problem Arbitrary solution: – Up -> high frequency input ~60 Hertz – Down -> lower frequency input ~30 Hertz
Problem Anatomy/network is ‘known’ – Reflex pathways – Neuron types – Inhibitory/excitatory connections Strength of connections is unknown
Representation of Connections Array of connection strengths & muscle fiber strengths: 0.23 | 1.43 | 2.3 | … | 0.21 631 Total Values Need to find a set of values that allows the model to behave properly. Inter-relation between values is very complex, i.e. non-linear.
Evolutionary Training Need to adjust the strengths of inter-neuron connections & muscle fiber strengths & … Population New Population Selection by fitness Crossover and Mutation Insert When the new population is full, evaluate the individuals and repeat ( potential) solutions w/ fitnesses
Fitness Root mean squared error Square root of the sum of the squared errors between actual and target motion at a series of points along the desired trajectory.
Conclusions Model is trainable Trainable with mixed variable types (connection strengths and muscle fiber strengths) Model produces fundamental biological behaviors Increasing complexity produced better behavior Model is robust, proper training helps
Future Work Train more complex behaviors Generalized movement Adaptation to injury Real robots ( w/simpler networks and neurons) – Non-pulse coded neurons – One `fiber’/actuator per muscle – Simpler networks – Known angles