Abstract
The automatic synthesis of embodied creatures through artificial evolution has become
a key area of research in robotics, artificial life and the cognitive sciences.
However, the research has mainly focused on genetic encodings and fitness functions.
Considerably less has been said about the role of controllers and how they
affect the evolution of morphologies and behaviors in artificial creatures. Furthermore,
the evolutionary algorithms used to evolve the controllers and morphologies
are pre-dominantly based on a single objective or a weighted combination of multiple
objectives, and a large majority of the behaviors evolved are for wheeled or
abstract artifacts.
In this thesis, we present a systematic study of evolving artificial neural network
(ANN) controllers for the legged locomotion of embodied organisms. A virtual but
physically accurate world is used to simulate the evolution of locomotion behavior
in a quadruped creature. An algorithm using a self-adaptive Pareto multi-objective
evolutionary optimization approach is developed.
The experiments are designed to address five research aims investigating: (1) the
search space characteristics associated with four classes of ANNs with different connectivity
types, (2) the effect of selection pressure from a self-adaptive Pareto approach
on the nature of the locomotion behavior and capacity (VC-dimension) of
the ANN controller generated, (3) the effciency of the proposed approach against
more conventional methods of evolutionary optimization in terms of computational
cost and quality of solutions, (4) a multi-objective approach towards the comparison
of evolved creature complexities, (5) the impact of relaxing certain morphological
constraints on evolving locomotion controllers.
The results showed that: (1) the search space is highly heterogeneous with both
rugged and smooth landscape regions, (2) pure reactive controllers not requiring
any hidden layer transformations were able to produce sufficiently good legged locomotion,
(3) the proposed approach yielded competitive locomotion controllers while
requiring significantly less computational cost, (4) multi-objectivity provided a practical
and mathematically-founded methodology for comparing the complexities of
evolved creatures, (5) co-evolution of morphology and mind produced significantly
different creature designs that were able to generate similarly good locomotion behaviors.
These findings attest that a Pareto multi-objective paradigm can spawn
highly beneficial robotics and virtual reality applications.